Vitamin D found to promote fat loss and muscle gain in women

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Higher levels of vitamin D are associated with a reduced risk of a variety of health issues including heart disease, type 2 diabetes and several forms of cancer. This research may be of some interest, but its nature (so-called ‘epidemiological’ studies) can’t tell us whether or not vitamin D actually protects against these conditions. It might be, for example, that healthier people are more likely to go outside and make vitamin D when exposed to sunshine.

Another example concerns the observation that individuals with low levels of vitamin D tend to be more prone to overweight and obesity. However, some have suggested that this might be because vitamin D tends to get sequestered (stored) in fat, removing it from the circulation and the more fat someone has, the more this tends to happen.

Studies that illuminate the role of vitamin D in health are those in which this substance is given to individuals to see what impact it has on them. Recently, a study was published in which vitamin D was given to a group of 77 overweight and obese women [1]. Half of the women were treated with 1,000 IU each day for 12 weeks, while the other half took a placebo. The vitamin D levels in the group taking this nutrients roughly doubled over the course of the study (an average of 38 nmol/l increasing to an average of 75 nmol/l) while the group taking placebo saw no significant increase.

Body weight was static over the course of the study in both groups, but the effects on body composition were not the same. Specifically, the group taking vitamin D ended up losing an average of 2.7 kg (6 lbs) of fat. At the same time, fat free mass (essentially, muscle) increased by an average of 1.8 kg. In those taking placebo, there was no significant change in fat mass or fat free mass.

In the paper, the authors refer to other work in which vitamin D has been mooted to assist in the development of lean body mass and inhibit the development of ‘adipocytes’ (fat cells). The authors also add that it is unclear whether the effect is due to the direct action of vitamin D or the ability of vitamin D to suppress levels of a hormone known as parathyroid hormone.

In the end, it might be hard to unpick the precise mechanisms involved here, What we do have, though, is a study which provides good evidence that maintaining generally higher levels of vitamin D in the body might bring genuine benefits for health.

The study also might remind us that while we can tend to be quite weight-focused, it can be possible to experience improvements in body composition (e.g. muscle gained and fat lost) without that registering on the scales.


1. Salehpour A, et al. A 12-week double-blind randomized clinical trial of vitamin D3 supplementation on body fat mass in healthy overweight and obese women. Nutrition Journal 2012;11:78

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