The traditional view that vitamin D is a nutrient solely required for bone heath has been largely superseded by research showing vitamin D is involved in a wide range of cellular functions unrelated to skeletal health. Clinical and epidemiological evidence shows associations between vitamin D and cancer, metabolic syndrome, obesity, type 1 diabetes, type 2 diabetes, multiple sclerosis and immunity from infection. As a result, a new category of vitamin D status has been created, in which individuals do not show signs of the traditional deficiency diseases of rickets and osteomalacia, but have low enough vitamin D status to cause serious health problem that may take years or decades to manifest. Such sub-clinical insufficiencies are being assessed in an increasing number of studies, with the elderly and those at high latitudes at particular risk, due to low sunlight exposure.
For example, researchers1 have used a cross sectional survey to assess the vitamin D status of 405 healthy free living men and women from Quebec in Canada. The subjects were aged between 68 and 82 years and had their 25-hydroxyvitamin D [25(OH)D] status assessed by radioimmunoassay. Vitamin D deficiency was found to be 12.6% and 8.7% for men and women in the winter months respectively. In the summer, these values fell to 5.7 and 1.9% for men and women, respectively. Serum 25(OH)D concentrations averaged 66.7 and 80.8nmols/L for men and women, respectively. Participants tested in summer or early autumn had serum 25(OH)D concentrations 13.8 nmol/L higher than those tested in winter. Age was not generally associated with vitamin D status within the population tested. Over 50% of the subjects tested had suboptimal vitamin D status according to the authors own comments (<75nmol/L).
Supplement use by the subjects was also recorded, with 47% of participants taking calcium/vitamin D supplements, 17% consuming vitamin D containing multivitamins and 10% consuming vitamin D alone. The usual supplementary dose of vitamin D was 400IU. Those consuming supplements had serum 25(OH)D concentrations 17.2 nmols/L higher than those who got their vitamin D only from their diet or sun exposure. The authors concluded that those individuals taking supplements were the least likely to have poor vitamin D status, suggesting that optimal levels of vitamin D are not attainable from food if living at latitudes as high as Quebec where sun exposure is limited. No toxicity was reported in any of the supplement users, suggesting that long term vitamin D intakes a the 400IU level are quite safe. In winter, no vitamin D deficiency was detected in the supplement users.
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