A lack of sunshine is not related with the lower vitamin D levels that are observed in older, heavier adults. Vitamin D is produced in skin exposed to sunlight, specifically ultraviolet B radiation. Fatter people are known to have less vitamin D in their blood. However, the reasons for this are not yet clear. It is likely that excess fat prevents the nutrient from reaching the bloodstream. One possible explanation could also be that heavier people spend less time in the sun or cover themselves up more. To investigate this further, researchers from the Tufts University in Boston studied 381 men and women aged 65 years or older and analysed the information gathered on the calcium and vitamin D supplementation to prevent bone loss. People were divided into four groups based on their body fat percentage. There was no difference among the groups in time spent outdoors, percent of skin exposed to the sun or sunscreen use. But the people with the highest percentage of body fat had 20 per cent lower blood levels of vitamin D than those with the least body fat. Low vitamin D levels are common in the US, and are known to increase the risk of osteoporosis. And an increasing number of chronic conditions are being linked to deficiency of vitamin D. The reason behind this could be that vitamin D gets trapped in fat tissue, so it is not available to the blood for circulation. This would occur even if vitamin D is consumed through diet and supplements, as well as vitamin D made in the skin during sun exposure. The results indicate that heavier people may need more vitamin D, whether it is from more sun exposure or getting more in the diet.
The Journal of Clinical Endocrinology & Metabolism,
August 2007