Vitamin D insufficiency is a term used to describe a status of sub-clinical deficiency of the hormone vitamin D3 (cholecalciferol) and its metabolites 25-hydroxyvitamin D3 [25(OH)D3], and 1, 25-dihydroxyvitamin D3 [1, 25(OH)2D3]. While deficiency of vitamin D was originally thought to lead only to the formation of rickets and osteomalacia in children and adults respectively, it is now known that low plasma levels are implicated in the development of a number of major diseases including multiple sclerosis, cancer and diabetes. Research suggests that levels of 25(OH)D3 in the blood should be above 50 ng / mL (125 nmol / L) in order to provide optimal vitamin D status. However, research repeatedly identifies that large proportions of the populations tested have 25(OH)D3 much below this optimal figure, some as low as 10 ng / mL.
Vitamin D insufficiency is particularly prevalent in high latitudes in the winter, when sun exposure drops because of the shorter days and lower incidence of the sun. For example, research published in the American Journal of Clinical Nutrition in 20101 measured the 25(OH)D3 in children (aged 12 to 22 months) in Dunedin in New Zealand (Latitude 45º south). The results showed that 94 % of the children had 25(OH)D3 above 20 ng / mL (50 nmol/L) in the summer. However, nearly 80 % of the children sampled in the winter had 25(OH)D3 levels below 20 ng / mL. Compared to the month of January (summer), concentrations of 25(OH)D3 were lower from April (autumn) through to (October) early spring. The mean monthly 25(OH)D3 level also mirrored the average monthly predicted UV index, with peak UV radiation occurring in December.
These results suggest that the 25(OH)D3 levels built up over summer were not enough to maintain levels throughout the winter. This is more evidence that dietary supplements of vitamin D3 are necessary in the winter for certain high latitude populations. This supports research from other studies that suggests that sun beds (here) or supplements (here) are necessary in order to maintain optimum levels of vitamin D. Supplements of vitamin D are available as cholecalciferol (vitamin D3) or ergocalciferol (vitamin D2). However, studies have shown that vitamin D3 is better at raising serum levels of 25(OH)D3 and 1, 25(OH)2D3 and is therefore the preferred choice (here). Most adults in high latitudes will require around 2000 iu of vitamin D3 per day in the form of supplements to maintain levels throughout the autumn, winter and spring months.
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