Population studies, vitamin requirements

Population studies to determine vitamin Bg nutritional status preferably require rapid and reliable methods to measure vitamin B. PLP is the predominant Bg vitamer in the circulation, and the plasma PLP level has been thought to be a... 

While the tryptophan load test is a useful index of status in controlled depletion/repletion studies to determine vitamin Bg requirements, it is not an appropriate index of status in population studies. 

Some 10-25% of the population have a genetic predisposition to hyperhomocysteinemia, which is a risk factor for atherosclerosis and coronary heart disease, as a result of polymorphisms in the gene for methylenetetrahydrofolate reductase. There is no evidence that supplements of vitamin Bg reduce fasting plasma homocysteine in these subjects, and like the tryptophan load test, the methionine load test may be an appropriate index of status in controlled depletion/repletion studies to determine vitamin Bg requirements, but not in population studies. 

The mean dietary intake of soy isoflavones in Asian populations consuming soy-based diets ranges from 20-40 mg isoflavones/day, with upper percentile consumer intakes of 70 mg/day (corresponding to around 1 mg/kg body weight). In the six month intervention studies in Western postmenopausal women, the effective dose for improved BMD was around 80-90 mg/day, while in the one year, randomized, double-blind, placebo controlled clinical trial, the effective dose was 54 mg/day. Overall, the dietary recommendation is to consume 50 mg isoflavones/day in combination with standard nutritional requirements for calcium and vitamin D. 

Epidemiological studies in Europe reveal an inverse relationship between plasma vitamin E levels and the incidence of ischaemic heart disease (Gey and Puska 1989), and the risk of angina pectoris appears to increase with low plasma levels of vitamins E, A and C (Rie-mersma et al., 1991). These interesting observations require further population-based controlled intervention trials with specific supplements of antioxidant vitamins (Gey etal., 1991). 

What has been reported previously leads to the question of who should receive calcium and vitamin D supplementation without causing harmful effects. Current data do not allow definite conclusions to be drawn, but require further independent confirmation, since in numerous large studies, combined calcium and vitamin D supplementation did not increase cardiovascular events, even in the most frail and elderly populations [lO ]. Nevertheless, it seems appropriate to correct calcium deficiency preferably by enhancing dietary intake and to target supplementation on individuals at high risk of fracture or in whom calcium and vitamin D deficiency is highly prevalent. 

---