Calcium

By Ann Prentice, PhD

Dietary surveys and milk supply data demonstrate that the calcium (figure 1) intake of many populations is below recommended levels but there is little evidence that this compromises bone health in terms of fracture risk. It is possible that the ability of the human body to adapt to differing levels of calcium intake is sufficiently powerful that calcium intake is largely irrelevant in this context, although treatment of those at greatest risk of osteoporosis with supplemental calcium may be beneficial. It is also possible that early life exposure to differing amounts of calcium, or nutrient-gene, nutrient-nutrient or nutrient-lifestyle interactions may alter calcium requirements, rendering some populations more at risk from the consequences of a low calcium intake than others. However, the recent demonstration that older women in Africa and Asia have poor bone mineral status, despite their low fracture incidence,^1-3 could also suggest that calcium intake is important in maintaining bone health but that protective factors, such as vitamin D and physical activity, reduce the likelihood of fracture. Since a low calcium intake may have a role in growth retardation⁴ and has been implicated in other diseases which can affect people in developing countries such as colon cancer and hypertension, especially pregnancy-induced hypertension,⁵ it is premature to assume that populations with a low calcium intake will not benefit from an increase towards recommended levels. Until the controversies surrounding human calcium requirements are resolved by future research, the question of what priority should be given by governments in developing countries to meeting population targets for calcium intake will remain difficult to answer.

Figure 1. Comparison of average calcium intakes in different countries. Data from A. Prentice, A. J Clin Nutr 1994;59(S);477S - 483S

References

1.	Aspray TJ, Prentice A, Cole TJ, Sawo Y, Reeve J, Francis FM (1996) Low bone mineral content is common but osteoporotic fractures are rare in elderly rural Gambian women. J Bone Mineral Research 11:1018-1024.
2.	Prentice A, Parsons TJ, Cole TJ (1994) Uncritical use of bone mineral density in absorptiometry may lead to size-related artifacts in the identification of bone mineral determinants. Am J Clin Nutr 60:837-842.
3.	Russel-Aulet M, Wang J, Thornton JC, Colt EWD, Pierson RN (1993) Bone mineral density and mass in a cross-sectional study of White and Asian women. J Bone Miner Research 8:575-582.
4.	Prentice A, Bates CJ (1993) An appraisal of the adequacy of dietary mineral intakes in developing countries for bone growth and development in children. Nutr Res Rev 6:51-59.
5.	Bucher HC, Guyatt GH, Cook RJ, et al. 1996 Effect of calcium supplementation on pregnancy-induced hypertension and pre-eclampsia, JAMA. 275:1113-1117.

Extracted from a larger position paper by Dr Prentice for the UN ACC/SCN dated November 1997, "Milk, Calcium and Osteoporosis with Special Reference to Developing Countries". Contact email ann.prentice@mrc-hnr.cam.ac.uk

Calcium recommendations for adults over 50 years
USA/Canada (1999)	1 200 mg/d	UK (1998)	700 mg/d
European Union (1993)	700 mg/d	WHO/FAO* (1974)	450 mg/d
A Joint WHO/FAO Expert Consultation on Vitamins and Minerals was held in Bangkok in 1998. Recommendations are forthcoming and will be available in hard copy and on the FAO webside. Contact: Guy Nantel, FAO, Via di Caracalla, 00100 Rome, Italy; tel 00 39 06 5705 2028; email guy.nantel@fao.org (Re: nutrient requirement)