Vitamin D is a hormone synthesised in the skin via the action of ultraviolet light on cholesterol. Vitamin D can be consumed from food, but foods containing high amounts of vitamin D are not commonly consumed in the Western diet. Sunlight is therefore the best source of vitamin D for most individuals. However, sunlight exposure for many is not high enough in frequency, duration or intensity to be able to maintain optimal vitamin D production, and combined with a diet deficient in vitamin D, this creates a situation whereby a large number of Westerners living at high latitudes are deficient in vitamin D. Current recommendations are therefore to increase sun exposure, or to consume supplements of vitamin D in order to maintain adequate vitamin D status. Particularly through the winter, when sunlight becomes relatively weak. However, studies suggest that while some are taking this advice, many still do not fully understand the importance of optimal vitamin D levels to health.
One of the main problems associated with poor vitamin D status is a disruption to the insulin control system, with the possible development of insulin resistance. Evidence suggests that those with low levels of 25-hydroxyvitamin D, the main active metabolite of vitamin D, are at increased risk of disorders of the insulin system. For example, in one study1, researchers investigated the association between 25-hydroxyvitamin D levels and the risk of diabetes in a large group of adult subjects. The results showed that the risk of diabetes fell as the 25-hydroxyvitamin D concentration of the blood increased. However, this association was found for white subjects but not black subjects. The researchers suggested that presence of the association between 25-hydroxyvitamin D and diabetes in white subjects was modified by variation in a gene which resulted in high or low amounts of the binding protein required by vitamin D for transport in the blood. However this modification did not occur in black subjects.
These results therefore suggest that genetic factors play a role in the association between vitamin D status and health, at least in white subjects. This is not surprising as people are biochemically individual and a large number of varieties of particular genes exist. This variation is a result of sexual reproduction within the limited gene pool, and such modifying effects can be found for many physical traits in all animals, including humans. However, despite modifying effects, the basic underlying principle that vitamin D status is mainly affected by sun exposure and diet is still valid, and optimising vitamin D through increased sun exposure and improved diet, perhaps involving the use of supplements, should be encouraged. Those at particular risk of vitamin D deficiencies include the very young, the elderly, the infirmed and those who spend much of the working day inside or underground. In many cases vitamin D supplements are the best way to ensure optimal vitamin D intake in these groups.
RdB
