The traditional role for vitamin D was one of allowing correct bone formation. In this regard, vitamin D deficiencies are associated with osteomalacia and rickets in adults and children, respectively. However, more recently the role for vitamin D in human physiology has widened considerably, and now associations between poor vitamin D status and a number of Western lifestyle diseases such as obesity and type 2 diabetes have been identified. Vitamin D deficiencies may increase the risk of obesity and type 2 diabetes because of changes to the normal regulation of blood sugar. In particular, vitamin D appear necessary for the correct function of the insulin system, and low levels of vitamin D may increase the risk of insulin resistance. The metabolic syndrome is a cluster of disorders that likely develop from desensitisation of the insulin receptor to its hormone and development of the metabolic syndrome increases the risk of type 2 diabetes, obesity and cardiovascular disease significantly.
While the association between low levels of vitamin D and obesity are well reported, it is not clear if supplemental vitamin D is beneficial at causing weight loss. However, studies have investigated the effects of vitamin D supplements during weight loss. For example, in one study1, researchers compared the weight loss in two groups of women who were undergoing a 12 month weight loss programme. The women were obese and between the ages of 50 and 75 years and had 25-hydroxyvitamin D (the accepted biomarker for vitamin D status) of between 10 and 32 ng/mL. This classified the women as vitamin D insufficient. The women in the study received 2000 IU of vitamin D per day or an equivalent placebo. The weight loss programme involved 225 minute per week aerobic exercise and a reduced calorie diet. After 12 months the vitamin D supplemented group showed an increase in 25-hydroxyvitamin D serum levels of 13.6 ng/mL whereas the placebo group showed a decrease of 1.3 ng/mL.
Interestingly, subgroup analysis showed that those women who experienced the largest increase in vitamin D status (25-hydroxyvitamin D above 32 ng/mL) lost an average of 8.8 kg of body weight, compared to 5.6 kg in those whose vitamin D status did not improve to the same degree. The women with replete vitamin D status also had larger decreases in waist circumference (-6.6 versus -2.5 cm) and lost more body fat percentage (-4.7 versus -2.6 %). The women who complied most closely to the vitamin D supplementation programme (as measured by the tablets they had remaining on study end) also showed significant decreases in systemic inflammation as measured by C-reactive protein levels (-1.18 mg/mL), compared to the non-compliant women (-0.46 mg/mL). However, a comparison of the treatment and placebo groups showed no benefits for weight loss with vitamin D supplementation. Therefore vitamin D supplements improve weight loss, but only in those subjects who experience repletion of their vitamin D status.
Dr Robert Barrington’s Nutritional Recommendation: This study is very interesting. If the traditional treatment versus placebo analysis is performed, no benefit is showed for vitamin D with regard weight loss. This is likely due to the fact that some of the subjects clearly did not comply with the request of the researchers to take their supplements and also because supplements have varying effects on vitamin D repletion in different subjects. However, when the endpoint of the study was changed to the actual serum levels of 25-hydroxyvitamin D, statistically significant improvements in weight loss were shown for the vitamin D replete group. Therefore vitamin D supplements are effective at benefiting weight loss, but only if they cause increases in plasma levels of vitamin D. As vitamin D has many other physiological roles and is increasingly being seen as beneficial to the health, supplements of around 2000 IU are recommended during winter months for all adults, irrespective of the desire to lose weight.
RdB
