Recently a couple of blogs have focused on the potential role that vitamin D may play in the regulation of body weight (see here and here). One of these blogs concerns a study which found that low. Levels of vitamin D were associated with increased body weight and waist circumference. This does not mean that vitamin D deficiency or insufficiency definitely causes fatty accumulation, but this possibility exists.
As a follow-on from this, I was interested to read about a study (as yet, unpublished) which assessed the relationship between vitamin D levels and weight loss on a reduced calorie diet (you can read about it here). In this study, conducted at the University of Minnesota in the USA, 38 obese men and women were put on a reduced calorie diet (750 calories less per day than their daily requirement) for 11 weeks. The researchers looked at the relationship between vitamin D levels and extent of weight loss in the study participants.
The report linked to above states that vitamin D insufficiency was noted in many of these individuals, which possibly reflects the previous research which suggests that vitamin D deficiency might have some part to play in the development of overweight/obesity.
However, perhaps more telling that this was the finding that there was a relationship between the vitamin D levels and the extent of weight loss: the higher the vitamin D levels, the greater the weight loss. Again, this study also cannot be used to conclude that vitamin D can assist weight loss. But it is another piece of evidence which ties vitamin D to body weight control.
What is required now are intervention trials in which the effect of supplemental vitamin D on body weight is assessed, either on its own, or as part of some weight-reducing regime (e.g. diet). If such studies show that vitamin D can promote weight loss, then we will have unearthed a potentially important factor in obesity. It will also help to explain why individuals can often find themselves lighter in the summer than in the winter.