If you have an optimal amount of vitamin D in your blood – which surprisingly few people actually do – you’ll have more muscle mass than if your vitamin D status is too low. Nutritionists at Mahidol University in Thailand concluded this from a small epidemiological study they did of 163 overweight but healthy men and women.
The researchers measured the concentration of 25-hydroxyvitamin D in the subjects’ blood and also measured their body composition using bioelectrical impedance analysis.
Although Thailand is a tropical country with a lot of sunshine, most of the participants had relatively low vitamin D levels in their blood. The researchers had expected this.
Other epidemiological studies have shown that high fat mass is often accompanied by low vitamin D levels. [PLoS Med. 2013;10(2):e1001383.] One of the reasons for this is that as a body becomes fatter the skin surface area increases less than the mass does. The amount of sunlight that the skin can absorb – and with it the amount of vitamin D that the body can synthesise – doesn’t increase as much as the person’s weight increases.
And, as you’d expect, the researchers found that participants with higher levels of vitamin D in their blood were the ones who had a lower fat percentage.
A high vitamin D level was also associated with more muscle mass.
A high vitamin D level helps muscle building, the researchers suspect. In in-vitro studies where researchers expose muscle cells to vitamin D, the muscle cells produce less myostatin as a result. [J Steroid Biochem Mol Biol. 2013 Jan;133:1-11.] In addition, muscles cells that get too little vitamin D break down muscle proteins faster. [Endocrinology. 2013 Nov;154(11):4018-29.]
So, as far as the researchers can tell from their statistical calculations, more vitamin D means more muscle mass. The statistical calculations also showed that a large fat mass has a negative effect on muscle mass.
The research results imply that overweight people might be able to increase their muscle mass by taking a vitamin D supplement. The researchers suggest that more research is needed to see whether this is indeed the case.
Vitamin D status is a determinant of skeletal muscle mass in obesity according to body fat percentage
Vitamin D deficiency is now being recognized as an emerging problem worldwide. Obesity has been found to be associated with lower serum 25-hydroxyvitamin D [25(OH)D] concentrations due to various mechanisms. There is increasing evidence showing the extraskeletal health benefit of vitamin D. Previous studies demonstrated the relationship between vitamin D and adiposity. However, the association between vitamin D status and skeletal muscle mass has not been established in healthy obese individuals in tropical countries. The aim of this cross-sectional study was to assess vitamin D status and its relationship to serum 25(OH)D concentrations and body composition, including skeletal muscle mass (SMM) and adiposity in healthy obese individuals without diabetes who live in Thailand, which is located near the equator.
We enrolled 163 obese Thai individuals (59.5% women) from the obesity clinic at the Ramathibodi Hospital, Mahidol University, in Bangkok, Thailand.
The prevalence of vitamin D deficiency (<20 ng/mL) and vitamin D inadequacy (<30 ng/mL) were 49 (30.1%) and 148 (90.8%), respectively. In all, 98% of the individuals with body mass index >35 kg/m2 had vitamin D inadequacy. Serum 25(OH)D concentrations were negatively associated with percent body fat (%BF) (r = ?0.23; P = 0.003). Moreover, vitamin D status was positively associated with SMM (r = 0.18; P = 0.03) and the association remained after controlling for body fat mass and age (P = 0.003). Interestingly, in the individuals with lowest tertile of %BF, multiple linear regression analysis revealed that the significant positive predictors of %SMM were vitamin D status and male sex; the negative predictor was the body mass index after adjusting for age and exercise duration.
Our study demonstrated the high prevalence of vitamin D deficiency in obese, Thai populations without diabetes. Vitamin D status was an independent predictor of %SMM of patients with lowest tertile of %BF. We speculated that adiposity might play a role in the relationship of vitamin D and SMM.