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Shedding light on obesity and vitamin D status

The worldwide prevalence of obesity (defined as a BMI greater than 30) has more than doubled in the last thirty years, largely as a result of lifestyle changes leading to many people having a greater energy intake than expenditure. According to a study published in The Lancet recently, with the exception of populations in sub-Saharan Africa, over-eating is now a more serious health risk than eating too little. Globally three million people per year die as a result of obesity, three times the number who die from malnutrition.
There is also an increasing prevalence of vitamin D insufficiency and deficiency, particularly in developed countries. For example, according to a recent article published in the British Medical Journal, more than half the adult population in the UK is vitamin D insufficient, and 16% are severely deficient in the winter and spring; alarmingly up to a quarter of UK children are vitamin D deficient. This growing public health problem is also largely the result of lifestyle changes. Endogenous synthesis through exposure of the skin to sunlight is the major source of vitamin D; dietary sources are limited. Today’s children and adolescents tend to spend less time outside than previous generations, and the message that over-exposure to sunlight increases the risk of melanoma has lead to general over-cautiousness. While the role of vitamin D in regulating calcium and phosphorus and in the mineralization of bone has long been established, more recent work has linked vitamin D deficiency to a range of conditions including untoward pregnancy outcomes, diabetes, cancer, cardiovascular disease and autoimmune diseases. Previous observational studies also noted a link between obesity and vitamin D deficiency, but studies on vitamin D supplementation and weight loss yielded inconsistent results; it was not known which of the conditions was the cause and which the effect.
Now a meta-analysis involving a total of over 42,000 people of European ancestry from six different countries has been published. Twelve SNPs related to BMI and four SNPs associated with vitamin D formulation were analysed in normal weight, overweight and obese subjects. The results indicate that a higher BMI leads to lower vitamin D levels, probably because this vitamin is fat-soluble, but that higher vitamin D levels have no effect on obesity.
It would thus be prudent to monitor vitamin D status in obese subjects and give supplementation if needed, but encouraging lifestyle changes to incorporate regular exercise outdoors would kill two birds with one stone and would be of benefit to all of us!