Vitamin D deficiency is known to lead to imbalances in calcium homeostasis, which can in turn cause osteomalacia in adults and rickets in children. In Western nations, the symptoms of vitamin D deficiency are quite rare, despite studies consistently showing that populations investigated often have low levels of vitamin D. This disparity relates to the severity of the deficiency. While serious deficiency must be present to initiate the formation of osteomalacia or rickets, in most cases this level is never attained. Instead chronic low levels remain just above the threshold for outright deficiency, creating long term insufficiencies of vitamin D. Recently this insufficient state has been found to significantly increase the risk of a number of diseases of blood sugar control including obesity, metabolic syndrome and type 2 diabetes. Evidence also suggest that insufficient vitamin D status is a risk factor for cancer. Those infrequently exposed to sunlight are at the greatest risk of developing vitamin D insufficiency.
Young children and the elderly are particularly at risk of vitamin D deficiency, mainly because they are often limited in sun exposure compared to adults. Studies have investigated the vitamin D status of both groups and consistently found that many individuals within study populations fall within the insufficient range for vitamin concentrations (measured as the 25-hydroxyvitamin D [25(OH)D] metabolite of vitamin D). For example, a group of 6 year old children were studied and their serum 25(OH)D measured1. The serum 25(OH)D concentrations ranged from 4 to 211 mmol/L, which put 6 % of the children at risk of severe deficiency (< 25 mmol/L 25(OH)D), 23.6 % deficient (25 to < 50 nmol/L 25(OH)D), 36.5 % sufficient (50 to < 75 nmol/L (25(OH)D), and 33.7 % optimal (> 75 nmol/L 25(OH)D). As expected the prevalence of vitamin D was highest in the winter at 51 % compared to the summer at 10 %, supporting the contention that sunlight plays a dominant role in preventing vitamin D deficiencies.
As has been shown previously, those children with the darkest skin, originating from countries such as African, Turkey, Asia and Morocco showed higher incidence of vitamin D deficiency (54 %) compared to those from Western Europe (18 %). As well as the biochemical aspects of vitamin D status, the researchers also used correlation statistics to investigate associations between vitamin D status and other factors. Household income was significantly inversely associated with the risk of vitamin D, supporting previous studies that show that poverty is a risk for disease. Television watching and playing outside were also associated with the vitamin D status of the children as would be expected for a hormone that is synthesised by the action of sunlight. Vitamin D status was also significantly associated with overall quality of life in the children. These data therefore show that vitamin D deficiency is a complex multifactorial condition, but which is primarily controlled by the availability of sunlight exposure.
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