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Chapter 8: Gender and Nutrition in the Global Burden of Disease, 1990 to 2020


Estimating Mortality
Mortality Estimates for 1990
The Burden of Disability
Risk Factors for Death and Disability
How the Burden of Risk Factors was Assessed
Results: The Contributions of Malnutrition to the Global Burden of Disease
Projections of Disease Burden, 1990-2020
Conclusions
References
Discussion
Annex to Gender and Nutrition in the Global Burden of Disease, 1990 to 2020

Christopher Murray and Alan Lopez1

1 This paper is based on the Summary of the Global Burden of Disease Study prepared by Phylidda Brown which in turn is based on the book edited by the authors entitled ‘The Global Burden of Disease’ and published by Harvard University Press in 1996.
In general, statistics on the health status of populations suffer from several limitations that reduce their practical value to policy makers.
· First, they are partial and fragmented. In many countries even the most basic data - the number of deaths from particular causes each year - are not available. Even where mortality data are available, they fail to capture the impact of non-fatal outcomes of disease and injury, such as dementia or blindness, on population health.

· Second, estimates of the numbers killed or affected by particular conditions or diseases may be exaggerated beyond their demographically plausible limits by well-intentioned epidemiologists who also find themselves acting as advocates for the affected populations in competition for scarce resources. If the currently available epidemiological estimates for all conditions were right, some people in a given age group or region would have to die several times over to account for all the deaths that are claimed!

· Third, traditional health statistics do not allow policy makers to compare the relative cost-effectiveness of different interventions, such as, for example, the treatment of ischaemic heart disease versus long-term care for schizophrenia. At a time when people’s expectations of health services are growing and funds are tightly constrained, such information is essential to aid the rational allocation of resources.

To address these, and other limitations of traditional health statistics, the World Bank, in collaboration with WHO, commissioned a new study of the Global Burden of Disease (GBD) in 1991 to provide a new holistic assessment of global (and regional) health conditions in 1990.

Most developing countries still have only limited information about how their populations die. One of the chief objectives of the GBD has been to develop comprehensive, internally-consistent estimates of how many people died of each major cause in 1990 worldwide. No such data set was available before the GBD began work. The methods are briefly described in the Annex. A selection of key results follows.

Estimating Mortality

Deaths were classified using a tree structure. The first level of disaggregation comprises three broad cause groups:

· Group I: Communicable, maternal, perinatal, and nutritional conditions.
· Group II: Non-communicable diseases.
· Group III: Injuries.
Each group was then subdivided into sub-categories: for example, cardiovascular diseases and malignant neoplasms (cancers) are two sub-categories of Group II. Beyond this level, there are two further disaggregation levels so that 107 individual causes for which codes have been included in the Ninth Revision of the International Classification of Diseases (ICD-9), such as tuberculosis, stomach cancer, or road traffic accidents, can be listed separately.

A demographic data set giving information on population size and the distribution of deaths for each region was developed especially for the GBD. Next, to reach estimates of the number of deaths by cause, we drew on four broad sources of data:

· Vital registration systems. These are complete only for the Established Market Economies and the Formerly Socialist Economies of Europe, although some vital registration information is available for all regions except China, India, and Sub-Saharan Africa (excepting South Africa).

· Sample death registration systems. In China, a set of 145 Disease Surveillance Points, representative of both rural and urban areas, and covering about 10 million people, provides information on deaths by cause. In India, Maharashtra State provides full medical certification for at least 80% of urban deaths, while a rural surveillance system including more than 1300 primary health care centres nationwide was used to assess rural death patterns.

· Epidemiological assessments. Epidemiologists have made estimates of deaths for specific causes, such as malaria, in certain regions. These estimates combine information from surveys on the incidence or prevalence of the disease with data on case-fatality rates for both treated and untreated cases.

· Cause-of-death models. Models are used to check the validity of existing data by putting demographic limits on epidemiological estimates. Such models estimate the distribution of deaths by cause in a population from historical studies of the relationship between the overall level of mortality in a population and deaths from broad groups of causes, such as cardiovascular diseases. The model developed for this study drew on a data set of 103 observations from 67 countries between 1950 and 1991.

Mortality Estimates for 1990

Worldwide, one death in every three is from a Group I cause (communicable, maternal, and perinatal conditions, and nutritional deficiencies). Virtually all of these deaths are in the developing regions. One death in ten is from Group III causes (injuries) and just over half of all deaths are from Group II causes (non-communicable diseases). Figure 13 shows the proportionate burden from each cause for developing and developed regions.

Figure 13: Deaths by broad cause group, 1990

Note: Cause-of-death models. Models are used to check the validity of existing data by putting demographic limits on epidemiological estimates. Such models estimate the distribution of deaths by cause in a population from historical studies of the relationship between deaths from 12 broad groups of causes, such as cardiovascular diseases and infectious diseases, and the total number of deaths. The models developed for this study drew on a dataset of 103 observations from 67 countries between 1950 and 1991.
More surprising, perhaps, is the finding that, for several major developing regions, more people already die of Group II causes than Group I causes. In Latin America and the Caribbean, there are almost twice as many deaths from non-communicable diseases as from Group I causes. In China, there are four-and-a-half times as many deaths from non-communicable diseases as from Group I causes. The balance has also tipped towards Group II causes in the Middle Eastern Crescent and the region comprising Asia beyond India and China, and the Pacific Islands. Only in India and Sub-Saharan Africa do Group I causes still dominate, accounting for 51% and 65% of deaths respectively.

When the estimates are expressed in terms of the probability of dying at a given age in a given region, a striking picture emerges. For adults under the age of 70, the probability of dying from a non-communicable disease is greater in both Sub-Saharan Africa and India than in the Established Market Economies. The results show that premature mortality rates from non-communicable diseases are higher in populations with high mortality and low income than in the industrialised countries, which is perhaps somewhat surprising and requires further research.

The health of men in the Formerly Socialist Economies of Europe is surprisingly poor. Based on 1990 death rates, men face a 28% risk of death between the ages of 15 and 60, the highest risk in any region except Sub-Saharan Africa. This excess is explained by a higher rate of non-communicable diseases and also by a higher risk of death from injury than for men in the Established Market Economies.

LEADING CAUSES OF DEATH IN 1990

Just over 50 million people died worldwide in 1990, with ischaemic heart disease (IHD) causing more deaths than any other disease or injury. Only 2.7 million of the 6.3 million people who died of IHD lived in the developed world. Cerebrovascular disease (stroke) killed 4.4 million people, of whom only 1.4 million were in the developed world. Lower respiratory infections (pneumonia) killed 4.3 million people, all but 0.4 million of them in the developing world. Diarrhoeal diseases caused 2.9 million deaths, virtually all in the developing world. The ten leading causes together accounted for just over half of all deaths (Table 7).

Table 7: The ten leading causes of death, 1990

Developed Regions

Developing Regions


Deaths
(‘000s)

Cumulative
%


Deaths
(‘000s)

Cumulative
%

All Causes

10,912


All Causes

39,554


1. Ischaemic heart disease

2,695

24.7

1. Lower respiratory infections

3,915

9.9

2. Cerebrovascular disease

1,427

37.8

2. Ischaemic heart disease

3,565

18.9

3. Trachea, bronchus and lung cancer

523

42.6

3. Cerebrovascular disease

2,954

26.4

4. Lower respiratory infections

385

46.1

4. Diarrhoeal diseases

2,940

33.8

5. Chronic obstructive pulmonary disease

324

49.1

5. Conditions arising during the perinatal period

2,361

38.7

6. Colon and rectum cancers

277

51.6

6. Tuberculosis

1,922

43.4

7. Stomach cancer

241

53.8

7. Chronic obstructive pulmonary diseases

1,887

46.1

8. Road traffic accidents

222

55.8

8. Measles

1,058

48.7

9. Self-inflicted injuries

193

57.6

9. Malaria

856

50.9

10. Diabetes mellitus

176

59.2

10. Road traffic accidents

777

52.8


INJURIES AND THE BURDEN OF SUICIDE

Worldwide in 1990, about 5 million people died of injuries of all types, two-thirds of them men. Most of these deaths are heavily concentrated among young adults. In this age group, road traffic accidents, suicide, war, fire, and violence are all among the ten leading causes of death.

Among adults aged 15-44 years worldwide, road traffic accidents were the leading cause of death worldwide for men and the fifth most important for women. For women between the ages of 15 and 44 years, suicide was second only to tuberculosis as a cause of death. In China alone, more than 180,000 women killed themselves in 1990. In India, women face an appallingly high risk of dying in fires: in 1990 alone, more than 87,000 Indian women died this way. In Sub-Saharan Africa, by contrast, the most important cause of injury deaths for both women and men is war.

The Burden of Disability

The GBD Study suggests that disability plays a central role in determining the overall health status of a population. Yet that role has until now been almost invisible to public health. The leading causes of disability are shown to be substantially different from the leading causes of death, thus casting serious doubt on the practice of judging a population’s health from its mortality statistics alone.

MENTAL ILLNESSES

Most significantly, the study shows that the burden of psychiatric conditions has been heavily underestimated. Of the ten leading causes of disability worldwide in 1990, measured as years lived with a disability (YLDs), five were psychiatric conditions: unipolar depression, alcohol use, bipolar affective disorder (manic depression), schizophrenia, and obsessive-compulsive disorder. Unipolar depression alone was responsible for more than one in every ten years of life lived with a disability worldwide. Altogether, psychiatric and neurological conditions accounted for 28% of all YLDs, compared with 1.4% of all deaths and 1.1% of years of life lost. The predominance of these conditions is by no means restricted to the rich countries, although their burden is highest in the Established Market Economies. They were the most important contributor to YLDs in all regions except Sub-Saharan Africa, where they accounted for a relatively modest 16% of the total.

The leading causes of disability are shown to be substantially different from the leading causes of death, thus casting serious doubt on the practice of judging a population’s health from its mortality statistics alone.

Alcohol use is the leading cause of male disability - and the tenth largest in women - in the developed regions. More surprisingly, perhaps, it is also the fourth largest cause in men in developing regions. The remaining important causes of YLDs were anaemia, falls, road traffic accidents, chronic obstructive pulmonary disease, and osteoarthritis (Table 8).

Table 8: The leading causes of disability, world, 1990


Total (millions)

% of Total

All Causes

472.7


1. Unipolar major depression

50.8

10.7

2. Iron deficiency anaemia

22.0

4.7

3. Falls

22.0

4.6

4. Alcohol use

15.8

3.3

5. Chronic obstructive pulmonary disease

14.7

3.1

6. Bipolar disorder

14.1

3.0

7. Congenital anomalies

13.5

2.9

8. Osteoarthritis

13.3

2.8

9. Schizophrenia

12.1

2.6

10. Obsessive-compulsive disorders

10.2

2.2


REGIONAL IMBALANCES IN THE BURDEN OF DISEASE

The peoples of Sub-Saharan Africa and India together bore more than four-tenths of the total global burden of disease in 1990, although they made up only 26% of the world’s population in that year. By contrast, the Established Market Economies and the Formerly Socialist Economies of Europe, with about a fifth of the world’s population between them, together bore less than 12% of the total disease burden. China emerged as substantially the most ‘healthy’ of the developing regions, with 15% of the global disease burden and a fifth of the world’s population. Put differently, about 579 years of healthy life were lost for every 1000 people in Sub-Saharan Africa, compared with just 124 for every 1000 people in the Established Market Economies, highlighting the massive inequalities of world health at the end of the 20th century.

TRADITIONAL ENEMIES REMAIN A SIGNIFICANT FORCE

Communicable, maternal and perinatal conditions, and nutritional deficiencies persist as a problem for the whole world. Even though these Group 1 conditions accounted for only 7% of the burden in the Established Market Economies and less than 9% in the Former Socialist Economies, they nevertheless made up more than four-tenths of the total global burden of disease in 1990, and almost half of the burden (49%) in developing regions. In Sub-Saharan Africa, two out of three years of healthy life lost were due to Group I conditions. Even in China, where the epidemiological transition is far advanced, a quarter of years of healthy life lost were due to this Group. Worldwide, five out of the ten leading causes of disease burden are Group I conditions: lower respiratory infections (pneumonia); diarrhoeal disease; perinatal conditions; tuberculosis; and measles. In developing countries, malaria is added to this already daunting list (Figure 14).

INJURIES ARE A LARGE, AND NEGLECTED, HEALTH PROBLEM IN ALL REGIONS

The burden of injury in 1990 was highest in the Formerly Socialist Economies of Europe, where almost 19% of all burden was attributed to this group of causes. China had the second highest injury burden, Latin America and the Caribbean the third, and Sub-Saharan Africa the fourth. Even in the Established Market Economies, however, the burden of injuries - dominated by road traffic accidents - was almost 12% of the total.

Figure 14: The burden of disease, by broad cause group, 1990

Note: EME: Established Market Economies; FSE: Formerly Socialist Economies; CHN; China; LAC: Latin America and the Caribbean; OAI: Other Asia and Islands; MEC: Middle Eastern Crescent.
In almost all regions, unintentional injuries were a much bigger source of ill-health in 1990 than intentional injuries such as interpersonal violence and war. The only exception was the Middle Eastern Crescent, where unintentional and intentional injuries took an approximately equal toll because of a particularly high burden of war in the region at the time.

LEADING CAUSES OF DISEASE BURDEN

When causes of death are compared, in rank order, with causes of disease burden, substantial differences emerge, again reinforcing the need to take non-fatal conditions into account as well as deaths when assessing a population’s health status. While a few leading conditions - such as lower respiratory infections, diarrhoeal diseases, and perinatal conditions - are at the top of both lists, there are 14 conditions in the top half of the list for disease burden that are in the bottom half of the list for deaths. Depression is the most marked of these, falling within the top ten for disease burden, but the bottom ten for deaths.

The leading causes of disease burden worldwide in 1990 were broadly similar to those for the developing regions. (Table 9).

Table 9: Ten leading causes of disease burden (DALYs), developing world, 1990


Total (millions)

% of Total

All Causes

1,218.2

9.1

1. Lower respiratory infections

110.5

8.1

2. Diarrhoeal diseases

99.2

7.3

3. Conditions arising during the perinatal period

89.2

3.4

4. Unipolar major depression

41.0

3.1

5. Tuberculosis

37.9

3.1

6. Measles

36.5

3.0

7. Malaria

31.7

2.6

8. Ischaemic heart diseases

30.7

2.5

9. Congenital anomalies

29.4

2.4

10. Cerebrovascular diseases

29.1

2.4


SEX DIFFERENCES IN DISEASE BURDEN

Although in infancy and early childhood, girls and boys suffer from broadly similar health problems, striking sex differences emerge in adults. First, and most obviously, women suffer disproportionately from their reproductive role. Although the burden of reproductive ill-health is almost entirely confined to the developing regions, it is so great that even worldwide, maternal conditions make up three out of the ten leading causes of disease burden in women between the ages of 15 and 44 years. In developing regions, five out the ten leading causes of DALYs are related to reproductive ill-health, including the consequences of unsafe abortion and chlamydia. Almost all of this loss of healthy life is avoidable.

However, poor reproductive health is far from being women’s sole concerns. In both developing and developed regions, depression is women’s leading cause of disease burden. In developing regions, suicide is the fourth. Thus, while programmes to reduce the unacceptably high burden of poor reproductive health must remain a high priority for years to come, women’s psychological health also deserves much more attention.

For men aged 15-44 years, road traffic accidents are the biggest cause of ill-health and premature death worldwide, and the second biggest in developing regions, surpassed only by depression. Alcohol use, violence, tuberculosis, war, bipolar affective disorder, suicide, schizophrenia and iron-deficiency anaemia make up the remainder of the list in developing countries. The high toll of road traffic accidents in developing regions has received relatively little attention from public health specialists in the past.

Risk Factors for Death and Disability

Exposure to particular hazards, such as tobacco, alcohol, unsafe sex or poor sanitation, can significantly increase individuals’ risks of developing disease. These hazards, or risk factors, are significant contributors to the total global disease burden and health policy makers need accurate information on their impact if they are to devise effective prevention strategies. Until now, however, there have been few attempts to measure the burdens of these risk factors, or to express them in a currency that can be compared directly with the burdens of individual diseases.

How the Burden of Risk Factors was Assessed

The burden of disease or injury in a population today that can be attributed to past exposure to a given risk factor is, essentially, an estimate of the burden that could have been averted in the population if that particular risk factor had been eliminated. More precisely, this is defined as the difference between the currently observed burden and the burden that would be observed if past levels of exposure had been equal to a specified, reference distribution of exposure. In general, to calculate this, it is necessary to know: (a) the relative risk at different levels of exposure for each cause of death and disability linked to the factor; (b) the distribution of different levels of exposure in the population; and (c) the burden of disease or injury due to each of the causes linked to the factor. Depending on the nature of the risk factor, the reference distribution against which relative risk is compared could be zero exposure for the whole population, a population distribution of exposure from low to high levels based on observed populations, or an arbitrary distribution. For this study, we used, wherever possible, zero exposure as the reference, except for risk factors such as hypertension, where clearly no one can be said to exposed to ‘zero’ levels.

Results: The Contributions of Malnutrition to the Global Burden of Disease

Of the ten risk factors studied, the most significant were malnutrition, poor water, sanitation and hygiene, unsafe sex, alcohol, tobacco, and occupation. Together, these six hazards accounted for more than one-third of total disease burden worldwide in 1990 (see Table 10). Of the six, malnutrition and poor sanitation were the dominant hazards, responsible for almost a quarter of the global burden between them. Unsafe sex and alcohol each contributed approximately 3.5% of the total disease burden, closely followed by tobacco and occupational hazards with just under 3% each. These are comparable to the burdens caused by tuberculosis and measles.

Not surprisingly, there are major inequalities between regions and between men and women in the burdens of most risk factors. For example, the ill-health consequences of unsafe sex - which include both infections and the complications of unwanted pregnancy - are borne disproportionately by women in all regions. In young adult women in Sub-Saharan Africa, unsafe sex accounts for almost one-third of the total disease burden.

...malnutrition and poor sanitation were the dominant hazards, responsible for almost a quarter of the global burden between them.
...Not surprisingly, there are major inequalities between regions and between men and women in the burdens of most risk factors.

Tobacco and alcohol currently cause their heaviest burdens in men in the developed regions. In these regions, the two together accounted for more than one-fifth of the total burden in 1990. However, the health burdens of smoking and drinking are far from being the exclusive preserve of the industrialised world. The recent rapid increase in tobacco use in Asia and other developing regions is expected to kill many more people in the coming decades than have so far died in the developed regions.

Table 10: Global burden of disease and injury attributable to selected risk factors, 1990

Risk Factor

Deaths
(‘000s)

As % of total deaths

YLLs
(‘000s)

As % of total YLLs

YDS
(‘000s)

As % of total YDS

DALYs
(‘000s)

As % of total DALYs

Malnutrition

5,881

11.7

199,486

22.0

20,089

4.2

219,575

15.9

Poor water supply, sanitation & personal & domestic hygiene

2,668

5.3

85,520

9.4

7,872

1.7

93,392

6.8

Unsafe sex

1,095

2.2

27,602

3.0

21,200

4.5

48,702

3.5

Tobacco

3,038

6.0

26,217

2.9

9,965

2.1

36,182

2.6

Alcohol

774

1.5

19,287

2.1

28,400

6.0

47,687

3.5

Occupation

1,129

2.2

22,493

2.5

15,394

3.3

37,887

2.7

Hypertension

2,918

5.8

17,665

1.9

1,411

0.3

19,076

1.4

Physical inactivity

1,991

3.9

11,353

1.3

2,300

0.5

13,653

1.0

Illicit drugs

100

0.2

2,634

0.3

5,834

1.2

8,467

0.6

Air pollution

568

1.1

5,625

0.6

1,630

0.3

7,254

0.5

Source: Murray and Lopez (1997)
The impact of alcohol varies between regions not only because of different levels of use in each population, but also because of differences in the age structure of those populations. Alcohol has consistently been shown to provide some protection against death from ischaemic heart disease, but to increase the risk of several other diseases, such as alcoholic psychoses, pancreatitis, some cancers and cirrhosis of the liver, as well as many injuries. Because of its protective effect against ischaemic heart disease, in populations where this condition is common and injuries and violence are rare, alcohol may prevent about as many deaths as it causes. In the Established Market Economies, for instance, this is probably the case. Nevertheless, alcohol causes a severe disease burden in these rich countries, because it causes so many injuries and premature deaths and thus results in large numbers of years lived with a disability and years of life lost.

In Sub-Saharan Africa, the picture is very different. There, ischaemic heart disease is relatively uncommon, so the protective effect of alcohol is far outweighed by its harmful effects in increasing the rates of death and disability from injuries. The contribution of alcohol to injuries is also extremely high in Latin America and the Caribbean, where alcohol use accounts for almost 10% of total disease and injury burden, a figure surpassed only in the developed regions. Ultimately, alcohol is estimated to have caused about three-quarters of a million more deaths in 1990 than it averted, with more than four-fifths of the excess deaths in the developing regions.

THE GLOBAL BURDEN OF MALNUTRITION

Mason and colleagues (personal communication) have developed estimates of the burden of disease attributable to the physiological state of undernutrition. Using data from 55 studies on the relative risk of mortality as a function of the z-score weight-for-age nutritional indicator, they estimated the relative risk per z-score for each region. The proportion of the population that was more than two z-scores below the median in a population distribution of weight-for-age was used to estimate the attributable fraction of child mortality in each region. Similar calculations were undertaken for morbidity, which shows lower relative risks and attributable fractions. No attempt was made to calculate the burden attributable to mild undernutrition, i.e., the population between one and two z-scores below the median.

There are no relevant studies on the relative risk of mortality from undernutrition for adults and thus the burden of disease attributable to undernutrition for the population aged 5-44 years is calculated by assuming that the relative risks for children aged 0-4 years were applicable to this adolescent and adult population as well. Unfortunately, no convincing evidence has been collected to support this relationship. We have, therefore, only included the attributable burden estimated for children in Table 11.

Table 11: Burden of disease attributable to underweight among children, 1990

Region

Deaths
(‘000s)

As % of total deaths

YLLs
(‘000s)

As % of total YLLs

YLDs
(‘000s)

As % of total YLDs

DALYs
(‘000s)

As % of total DALYs

Established market economies

0.0

0.0

0

0.0

0

0.0

0

0.0

Formerly Socialist economies

0.0

0.0

0

0.0

0

0.0

0

0.0

India

1,722.0

18.4

58,086

29.0

6,450

7.4

64,536

22.4

China

278.0

3.1

9,366

7.9

1,781

2.0

11,147

5.3

Other Asia and islands

679.0

12.3

23,037

20.1

2,721

4.3

25,758

14.5

Sub-Saharan Africa

2,619.0

31.9

89,305

39.4

7,129

10.4

96,434

32.7

Latin America & the Caribbean

135.0

4.5

4,540

8.1

520

1.2

5,039

5.1

Middle Eastern Crescent

447.0

9.8

15,152

14.4

1,489

3.3

16,641

11.0

World

5,881.0

11.7

199,486

22.0

20,089

4.2

219,575

15.9

Developed Regions

0.0

0.0

0

0.0

0

0.0

0

0.0

Developing Regions

5,881.0

14.7

199,486

24.3

20,089

5.1

219,575

18.0

Source: Murray and Lopez (1996)
Even limiting the estimates of the burden of disease due to malnutrition to the effects of underweight in children, it is a major cause of disease burden in regions such as Sub-Saharan Africa where it accounts for one-third of all DALYs lost from disease and injury. In India malnutrition accounts for 22% of disease burden, and elsewhere in Asia and the Pacific Islands about 15%. Based on this analysis child malnutrition is negligible as a source of DALYs in more developed regions. This picture may be very different, however, if micronutrient malnutrition were taken into account. This work is yet to be done. Similarly, underweight in adults and overnutrition in all age groups, once taken into account, may have an important impact on these results.

Projections of Disease Burden, 1990-2020

Rather than attempt to model the effects of the many separate direct, or proximal, determinants of disease from the limited data that are available, it was decided to consider a limited number of socioeconomic variables: (1) income per capita; (2) the average number of years of schooling in adults, termed ‘human capital’; and (3) time, a proxy measure for the secular improvement in health this century that results in part from accumulating knowledge and technological development. These socio-economic variables show clear historical relationships with mortality rates: for example, income growth is closely related to the improvement in life expectancy that many countries have achieved this century. Because of their relationships with death rates, these socioeconomic variables may be regarded as indirect, or distal, determinants of health. In addition, a fourth variable, tobacco use, was included, because of its overwhelming impact on health status, using information from more than four decades of research on the time lag between persistent tobacco use - measured in terms of ‘smoking intensity’ - and its effects on health.

Death rates for all major causes based on historical data for 47 countries since 1950-91 were related to these four variables to estimate the parametric values for each age/sex group, which was then used to generate the projections. A separate model was used for HIV and modifications for the interaction between HIV and tuberculosis. Three projection scenarios were developed using different projections of the independent variables.

THE IMPACT OF INFECTIOUS DISEASE MAY BE REDUCED

Deaths from communicable, maternal, and perinatal conditions, and nutritional deficiencies (Group I) are expected to fall from 17.3 million in 1990 to 10.3 million in 2020. As a percentage of the total burden, Group I conditions are expected to drop by more than half, from 34% to 15%.

This projected reduction overall, despite increased burdens due to HIV and tuberculosis, runs counter to the now widely-accepted belief that infectious diseases are making a comeback worldwide. It reflects, in part, the relative contraction of the world’s ‘young’ population: the under 15 age group is expected to grow by only 22% between 1990 and 2020, whereas the cohort of adults aged between 15 and 60 is expected to grow by more than 55%. In addition, the projection reflects the observed overall decline in Group I conditions over the past four decades, due to increased income, education, and technological progress in the development of antimicrobials and vaccines. Even under the pessimistic scenario, in which both income growth and technological progress are expected to be minimal, deaths from these conditions are still expected to fall slightly to 16.9 million.

Clearly, it should not be taken for granted that the progress of the past four decades against infectious diseases will be maintained. It is possible, for example, that antibiotic development and other control technologies will not keep pace with the emergence of drug-resistant strains of important microbes such a Mycobacterium tuberculosis. If such a frightening scenario were to prove correct, and if case-fatality rates were to rise because of such drug-resistant strains, the gains of the present century could be halted or even reversed. Undoubtedly, the continuing high toll of Group I causes today leaves no room for complacency.

Nonetheless, the evidence to date suggests that, as long as, and only if, current efforts are maintained, Group I causes are likely to continue to decline.

TOBACCO’S LEGACY

By 2020, the burden of disease attributable to tobacco is expected to outweigh that caused by any single disease. From its 1990 level of 2.6% of all disease burden worldwide, tobacco is expected to increase its share to just under 9% of the total burden in 2020, compared with just under 6% for ischaemic heart disease, the leading projected disease. This is a global health emergency that many governments and international health agencies have yet to confront.

LEADING CAUSES OF DISEASE BURDEN IN 2020

In 1990, the three leading causes of disease burden were, in descending order, pneumonia, diarrhoeal diseases, and perinatal conditions. The three conditions projected to take their place by 2020 are ischaemic heart disease, depression, and road traffic accidents. Pneumonia is expected to fall to sixth place, diarrhoeal diseases to ninth, and perinatal conditions to eleventh. Notably, measles, currently in eight place, is expected to drop to twenty-fifth. However, not all infectious diseases are expected to decline, despite the projected overall decrease of Group I conditions. Tuberculosis is expected to remain at its current level of seventh place, a substantial source of disease burden for the foreseeable future. Of perhaps even greater concern is the finding that HIV, currently twenty-eighth in the ranking, could be as high as tenth by 2020.

ROAD TRAFFIC ACCIDENTS AND VIOLENCE

Because of the growth of the adult fraction of the population, the burdens of several important types of injury are also likely to increase. For example, young men are the population group most frequently involved in road traffic accidents, so if the young-adult proportion of the population increases sharply, road traffic accidents are likely to increase too. Indeed, according to the baseline projection, road traffic accidents could rise to third place from ninth worldwide. Violence, currently nineteenth, could rise as high a twelfth place, and suicide could climb from seventeenth to fourteenth place.

Non-communicable diseases were already, in 1990, the leading causes of death worldwide and the leading cause of disease burden.

Not surprisingly, these changes are not expected to be evenly dispersed worldwide. The total number of lost years of healthy life in the Established Market Economics is likely to fall slightly, while it will increase slightly in the Formerly Socialist Economies of Europe. Strikingly, however, Sub-Saharan Africa’s future looks disturbingly poor despite the decline in the burden of Group I conditions that currently dominate its health needs. Overall, the region faces an increase in the number of lost years of healthy life between 1990 and 2020, due mainly to a steep projected rise in the burden of injuries from road accidents, war and violence.

Conclusions

Several surprising findings emerged from this first ever attempt to quantify global health status. Perhaps most surprising was the fact that non-communicable diseases were already, in 1990, the leading causes of death worldwide and the leading cause of disease burden. By measuring non-fatal outcomes in a comparable fashion to premature death, the massive, but hitherto unknown disease burden from neuropsychiatric conditions, especially depression, emerges as a major global public health concern. Similarly injuries, whether intentionally or unintentionally inflicted, are a significant cause of burden in all regions, typically accounting for around 10% of the entire disease and injury burden. Projections to the year 2020 carried out as part of the GBD Study suggest that the significance of non-communicable diseases will increase even further in all regions, but particularly in China, Latin America and the Caribbean, and parts of Asia. Even in Sub-Saharan Africa, chronic diseases by 2020 are projected to cause as many deaths as all infectious diseases combined. Other leading health concerns, including malnutrition and malaria, will remain so unless concerted action is taken to reduce their toll. But perhaps the greatest challenge to public health will be to reduce the impact of the two great public health pandemics of the late 20th century, tobacco and HIV.

References

Murray CJL and Lopez AD (eds) (1996) The Global Burden of Disease. The Harvard School of Public Health on behalf of the WHO and the World Bank, Harvard University Press, Boston.

Murray CJL and Lopez AD (1997) Global mortality, disability, and the contribution of risk factors: Global Burden of Disease Study. Lancet 349:1436-42.

Discussion

Nevin Scrimshaw (UNU): In the 1960s, there was the PAHO study by Serrano and Puffer, and more recently the study by Pelletier of Cornell University, indicating that when one looked at deaths from infectious diseases in developing countries, nutrition was a major contributing factor in about half of them. The contribution of malnutrition to mortality was missed in the official vital statistics. We had similar findings on a smaller scale in an INCAP study in four villages. How can you take into account nutrition as a major contributory factor to deaths when it is not recorded?

Alan Lopez: In fact, that is Part 3 of the Study. It is a very interesting issue that applies not only to nutrition, but also, for example, to diabetes. I didn’t even mention today that diabetes is an outcome and also a risk factor for several major vascular conditions. In this study we looked at malnutrition - undernutrition, to be more specific - as a risk factor for this host of conditions. We did not try to quantify how it came out individually according to disease, but rather how malnutrition contributed to the burden of disease across a host of conditions. Those are the estimates that I’ve tried to present. I don’t know whether they’re right. This is the kind of community that should be providing input back to us saying that they’re either over- or underestimates. Malnutrition is considered in the same way as, for example, war, as a risk factor. I’ve presented results from war as an outcome, but war also could be looked at as a risk factor because it causes a host of conditions in health - not just the outcome of death or disability as a war-related event.

Aileen Robertson (WHO): I’m glad that you qualified the term “malnutrition” by saying “undernutrition” since clearly unhealthy nutrition and excessive intake of nutrients also contribute to the burden of disease. In your paper you predict that there will be a 77% increase in non-communicable diseases. You go on to say that the burden of disease of NCD is largely driven by population ageing and tobacco with no mention of nutrition. I feel that this is a lost opportunity for improving public health. On the one hand, you say that the major killers are NCDs and on the other, you state that “malnutrition” has zero effect. Clearly this is not the case and is misleading policy makers responsible for public health strategies. In the Former Soviet Union and in Europe, unhealthy nutrition is one of the major causes of NCDs, therefore, your “burden of disease” model does not help to convince policy makers of this fact. Your approach is a major obstacle to getting nutrition on the political agenda. I don’t know what can be done to address this problem. The question is do we have to wait for the next proposed set of DALYs before this error can be corrected?

Alan Lopez: That is also a very good issue and thank you for raising it. More broadly in Europe, there is a tremendous public health problem that we are not quantifying very reliably. We don’t know, to my knowledge, reliably what is the contribution of overnutrition or poor nutrition in Central and Eastern Europe, nor indeed, do we know about alcohol. There is suspicion that a lot of this rise in mortality is due to alcohol, but we don’t know reliably. I feel that issues such as this, that are major public health problems, need to be more reliably quantified. I’m not saying that we got it all right - this was a global, macro-regional study. Within the macro-region (of the Former Socialist Economies of Europe, FSE), we’ve attributed virtually no DALYs to poor nutrition, and that clearly is not correct.

Urban Jonsson (UNICEF): Your presentation consisted of two major parts: mortality analysis, and this other meta-physical concept of DALYs. The mortality analysis I fully accept and I think that most of your sensible conclusions could have been shown with conventional mortality analysis. There is one thing that we are sure about - that we will all die one day. Many people don’t care what they die of if they live long, but we are all concerned about young people dying - in particular, children. There is no scientific method to assess the value associated with living longer. In the theory of science, we separate between science and meta-physics. Why do we do that? We do that to avoid the type of thing that we have seen here, because the DALY concept fulfils all the criteria for metaphysics. There are basically too many value judgements. The method that you have designed only says that you believe that average is right. It would be a terrible society if we believed that. Also, in the rank theory that you use, you know very well that it doesn’t matter that much where the convergence of value judgement comes - you get the same picture. I know for example, people in wheelchairs who tell me that their life is actually richer after their accident. How do you account for all these complexities? How can we predict things this way? If your model had been used in 1985 for the Soviet Union - would it have predicted the break down of the Soviet Union and predicted these diseases? Finally, from a human rights perspective, the right of people to be healthy and alive tells me that this type of analysis is fundamentally not only unscientific, but is totally unethical.

Graeme Clugston (WHO): I must say that your transparency about the uncertainties is appreciated. You mentioned about 40 countries that have used this methodology in some way for readjusting priorities, or spending, or adjusting their emphasis on public health policy. Could you say a little more about that? Have you in any way been able to look at the changes that they’ve brought about as a result of using this methodology? Concerning the huge growing problem of obesity in children and adults, the Nutrition Programme at WHO has a growing global database on body mass index for both children and adults, which we would like to share with you.

Alan Lopez: Let me deal with those questions in reverse order. I have not been that involved in the country studies. That is not something that WHO has been particularly concerned with. We were involved in the global and regional part only. Most of the country studies have been done at Harvard. There are around 40 studies that are either completed, or are being carried out, or are planned. In the studies that have been completed, for example, in Mexico, it was found that the health information system was completely inadequate. They were not quantifying or measuring disability in any way that was useful. They were not even using the cross-sectional disability data that they were collecting. They did find, however, that it was going to be helpful if they applied this longitudinal concept. They also found that a lot of their cause-of-death information for violence was being miscoded. What burden of disease methods do is make you go into your data system and be critical about how you’re capturing various conditions. In terms of public health policy in Mexico, they have now established a public health foundation that they are using to try and address some of the inequities that I very quickly showed.

Coming back to the other issue, it is important that we are very clear what DALYs are and what DALYs are not. We could debate these kinds of questions for a long time, but I will be very brief. If you do not try to quantify non-fatal outcomes, you will perpetuate the omission of issues such as the neuro-psychiatric conditions, maternal anaemia and all of those leading causes of disability that we found in our study. The idea was that we tried to present to health care providers and those responsible for health care allocation, a holistic view not only of who dies of what, but of who is disabled and from what.

Annex to Gender and Nutrition in the Global Burden of Disease, 1990 to 2020

By Christopher Murray and Alan Lopez

Defining a Metric to Measure Disease Burden

In order to capture the impact of both premature death and disability in a single measure, a common currency is required. Time is an appropriate currency, measured as time (in years) lost through premature death, and time (in years) lived with a disability. A range of such time-based measures has been developed in different countries, many of them variants of the so-called Quality-Adjusted Life Year or QALY. For the GBD, an internationally standardised form of the QALY has been developed, called the Disability-Adjusted Life Year (DALY). The DALY expresses years of life lost to premature death and years lived with a disability of specified severity and duration. One DALY is thus one lost year of healthy life. Here, a ‘premature’ death is defined as one that occurs before the age to which the dying person could have expected to survive if they were a member of a model population with a life expectancy at birth equal to that of the world’s longest-surviving populations, namely Japan.

To calculate total DALYs for a given condition in a population, years of life lost (YLLs) and years lived with disability of known severity and duration (YLDs) for that condition must each be estimated, and then the total summed. For example, to calculate DALYs incurred through road traffic accidents in India in 1990, the total years of life lost in fatal road accidents are added to the total years of life lived with disabilities by survivors of such accidents.

It might appear that quantifying disease burden is a neutral exercise, entirely free of value choices. However, this is far from the case. Disease burden is, in effect, the gap between a population’s actual health status and some ‘ideal’, or reference status. In order to measure burden, a society has to decide what the ideal or reference status should be. This involves making five value choices:

· How long ‘should’ people live? If one is to estimate how many years of life are lost through death at any given age, we must decide on the number of years for which a person at that age should expect to survive in the ideal, or reference, population. That could be, for example, 60, 80, or 90 years from birth.

· Are years of healthy life worth more in young adulthood than in early or late life?

· Is a year of healthy life now worth more to society than a year of healthy life in 30 years’ time?

· Are all people equal? For example, should one socioeconomic group’s years of healthy life count for more than another’s?

· How do you compare years of life lost due to premature death and years of life lived with disabilities of differing severity?

HOW LONG SHOULD PEOPLE LIVE?

In accordance with the GBD’s egalitarian principles, the study assumes a standard life table for all populations, with life expectancies at birth fixed at 82.5 years for women and 80 years for men. A standard life expectancy allows deaths in all communities at the same age to contribute equally to the burden of disease. Alternatives, such as using different life expectancies for different populations that more closely match their actual life expectancies, are inconsistent with the egalitarian principle. For example, if a 25-year-old woman dies in childbirth in an African country where she might have expected to live another 30 years, her years of life lost would be deemed unfairly to be fewer than those for a 35-year-old woman who dies in childbirth in Japan, when she might otherwise have expected to live another 48 years.

Life expectancy is not equal for men and women. Accordingly, the GBD has given men a lower reference life expectancy (80 years) than that of women (82.5 years).

ARE YEARS OF HEALTHY LIFE WORTH MORE IN YOUNG ADULTHOOD THAN IN EARLY OR LATE LIFE?

If individuals are forced to choose between saving a year of life for a 2-year-old and saving it for a 22-year-old, most prefer to save the 22-year-old. A range of studies confirms this broad social preference to ‘weight’ the value of a year lived by a young adult more heavily than one lived by a very young child or an older adult. Adults are widely perceived to play a critical role in the family, community, and society. We therefore incorporated age-weighting into the DALY by assuming that the relative value of a year of life rises rapidly from zero at birth to a peak in the early twenties, after which it steadily declines.

IS A YEAR OF HEALTHY LIFE NOW WORTH MORE TO SOCIETY THAN A YEAR OF HEALTHY LIFE IN 30 YEARS’ TIME?

If a person is offered $100 today or $100 in a year’s time, that person is likely to prefer $100 today. Future dollars are thus discounted - valued lower - against current dollars. Whether a year of healthy life, like a dollar, is also deemed to be preferable now rather than later, is a matter of intense debate among economists, medical ethicists, and public health planners, because discounting future health affects both measurements of disease burden and estimates of the cost effectiveness of an intervention.

There are arguments for and against discounting. We decided, however, to discount future life years by 3% per year. This means that a year of healthy life bought for 10 years hence is worth around 24% less than one bought for now, as discounting is represented as an exponential decay function.

Discounting future health reduces the relative impact of a child death compared with an adult death. For example, with age-weighting also incorporated, a 1-year-old girl’s death causes a loss of 34 years of life while a 25-year-old woman’s death results in a loss of 33 years of life. Discounting also reduces the value of interventions that pay off largely in the future-such as vaccinating against hepatitis B, which may prevent thousands of cases of liver cancer, but only some decades later.

HOW DO YOU COMPARE TIME LOST DUE TO PREMATURE DEATH WITH TIME LIVED WITH DISABILITY?

While death is not difficult to define, disability is. All non-fatal health outcomes of disease are different from each other in their causes, nature, and their impact on the individual, and the impact on the individual is in turn mediated by the way the surrounding community responds. Yet, in order to quantify time lived with a non-fatal health outcome and assess disabilities in a way that will help to inform health policy, disability must be defined, measured, and valued in a clear framework that inevitably involves simplifying reality.

There is surprisingly wide agreement between cultures on what constitutes a severe or a mild disability. For example, a year lived with blindness appears to most people to be a more severe disability than a year lived with watery diarrhoea, while quadriplegia is regarded as more severe than blindness. These judgements must be made formal and explicit if they are to be incorporated into measurements of disease burden.

Two methods are commonly used to formalise social preferences for different states of health. Both involve asking people to make judgements about the trade-off between quantity and quality of life. This can be expressed as a trade-off in time (how many years lived with a given disability would you trade for a fixed period of perfect health?) or a trade-off between persons (would you prefer to save one life-year for 1000 perfectly healthy individuals as opposed to saving one life-year for 2000 individuals in a worse health state?). While such trade-offs may affront our perceptions about what is morally acceptable, they are practised implicitly throughout the world’s health care system. The philosophy of the GBD is that the more explicitly these preferences are set out, the more meaningfully they may be debated.

The GBD therefore developed a protocol based on the person trade-off method. In a formal exercise involving health workers from all regions of the world, the severity of a set of 22 indicator disabling conditions - such as blindness, depression, and conditions that cause pain - was weighted between 0 (perfect health) and 1 (equivalent to death). These weights were then grouped into seven classes where class I has a weight between 0.00 and 0.02 and Class VII a weight between 0.7 and 1 (see Table 12).

In essence, the weight is set by the number of people with a given condition whose claim on a fixed health care budget is equal, in the judgement of a participant, to that of 1000 entirely healthy people. For example, if the participant judges that 1000 entirely healthy people were judged to have an equal claim on the resources as 2000 people with a particular, less severe, disability, the weight assigned would be equal to 1 minus 1000 divided by 2000, or 0.5.

Table 12: Gauging the severity of disability: disability classes and weights set by the GBD protocol for 22 indicator conditions

Disability Class

Severity weights

Indicator conditions

1

0.00-00.2

Vitiligo on face, weight-for-height less than 2 standard deviations

2

0.02-0.12

Watery diarrhoea, severe sore throat, severe anaemia

3

0.12-0.24

Radius fracture in a stiff cast, infertility, erectile dysfunction, rheumatoid arthritis, angina

4

0.24-0.36

Below-the-knee amputation, deafness

5

0.36-0.50

Recto vaginal fistula, mild mental retardation, Down’s syndrome

6

0.50-0.70

Unipolar major depression, blindness, paraplegia

7

0.70-1.00

Active psychosis, dementia, severe migraine, quadriplegia

Note: These weights were established using the person trade-off method with an international group of health workers who met at WHO in Geneva in August 1995, Each condition is actually a detailed case. For example, angina in this exercise is defined as reproducible chest pain, when walking 50 metres of more, that the individual would rate as a 5 on a subjective pain scale from 0 to 10.


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