Evidence suggests that large numbers of people are at risk of vitamin D insufficiency because for part or all of the year, their 25-hydroxyvitamin D [25(OH)D] plasma concentrations drop below 75nmols/L. Exposure to ultra violet B radiation is the most effective way to improve vitamin D status, but for some at risk groups, regular sun exposure is sometimes not possible. Because of this, interest in the effects of dietary supplements of vitamin D3 has increased, and nutritional research is starting to accumulate data regarding the safe and effective intakes of vitamin D supplements necessary to raise 25(OH)D levels above 75nmol/L. The recommended intake for vitamin D in the diet varies depending on the country of origin, but is in the range of 200 to 400IU per day. However, this may be too low to achieve the optimal 25(OH)D plasma concentrations in the absence of significant sun exposure.
Researchers1 have investigated the effects of vitamin D supplementation, with or without calcium, on 92 adult men and women living in the South Eastern United States. Subjects received either 800IU of vitamin D per day in the vitamin D3 form, 2000mg calcium per day, or both. The study was placebo controlled and so some of the subjects acted as controls. At baseline, only 18% of the subjects had adequate vitamin D status, with 82% being insufficient [plasma 25(OH)D <75nmols/L] and with 28% having hypovitaminosis D [plasma 25(OH)D <37.5nmol/L]. Irrespective of the use of calcium, vitamin D supplementation raised plasma concentrations of 25(OH)D by 25 to 26nmol/L, but only half of the study participants had adequate 25(OH)D status >75nmols) after 6 months. Therefore 800IU is not a sufficient daily dose of vitamin D3 to raise plasma 25(OH)D to adequate levels in a majority of individuals.
As has been reported in other studies, those of African descent had the lowest levels of 25(OH)D due to the darker pigmentation of the skin. The data in this study supports a growing body of literature that suggests that large numbers of the population are not receiving enough dietary vitamin D, even taking into account supplement use. The fact that a large proportion of the population is vitamin D insufficient has important repercussions in other research areas, because it becomes obvious that most clinical trials are in fact using populations of individuals who are largely vitamin deficient. The 800IU supplied by the supplement in this study is higher than the recommended dietary intake of most countries and a much larger intake than would be possible in the diet alone. However, despite this, the supplement was still not able to raise 25(OH)D levels above 75nmol/L in most individuals.
RdB
