Q J Med 2002; 95: 485
© 2002 Association of Physicians
Correspondence |
Folic acid and the elderly
Harley Street, London
Sir,
Dr Rydlewicz and colleagues have shown the effect of folic acid supplementation on plasma homcysteine in an elderly population.1 The supposition is that the relationship is causal; a lower homocysteine level reduces the risk of vascular disease. Homocysteine levels >10.2 µmol/l double the risk of vascular disease compared with those below, while levels >20 µmol/l lead to a 10-fold increase.2 This is a remarkably steep rise over the lower range of plasma homocysteine concentrations.
In pernicious anaemia, however, there is often a plasma homocysteine level of 200 µmol/l without risk of vascular disease. A close correlation over a lower range thus does not safely allow extrapolation over the full range. The explanation of the anomaly lies in the increased blood flow that occurs with any anaemia. Increased blood flow from any cause decreases the incidence of vascular disease, while decreased blood flow leads to an increase in vascular disease.3
When there is reduced flow in the microcirculation, as seen in thalassaemia minor and the polycythaemia of high altitudes, but increase in the macrocirculation, it is the latter that wins. It may be a straw in the wind that so many malariologists became centenarians, but they probably had a low haemocrit over much of their working lives.
References
1. Rydlewicz A, Simpson JA, Taylor RJ, et al. The effect of folic acid supplementation on plasma homocysteine in an elderly population. Q J Med2002; 95:27–35.
2. Carmel R, Jacobsen DW. Homocysteine in Health and Disease. Cambridge, CUP, 2001.
3. Fowler PBS. The thyroid, blood flow, and atheroma. Q J Med2000; 93:477–85.
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