Study under review: Effects of Vitamin D Supplementation on Serum 25-Hydroxyvitamin D Concentrations and Physical Performance in Athletes: A Systematic Review and Meta-analysis of Randomized Controlled Trials
Vitamin D’s reach across the body is far and wide. Its receptor exists in pretty much all tissues, and it’s probably there for a reason. But, that reason differs depending on the tissue in question. This review focuses on muscle.
When vitamin D binds its receptor, the complex goes to the nucleus and affects the transcription of genes. In muscle cells, this process affects genes related to calcium handling (which is essential for muscle contraction) as well as genes involved in muscle cell development and proliferation. Also, some mutations in the vitamin D receptor are correlated with changes in muscle strength. Finally, mouse experiments that delete the vitamin D receptor show direct effects on muscle. So, mechanistically, these suggest that vitamin D and its receptor impact muscle. Some of the physiological effects of vitamin D and its receptor on muscle cells are summarized in Figure 1.
While muscle function is important for everyone, it’s of particular concern to athletes. In fact, it may be doubly concerning, since vitamin D deficiency is prominent even in these paragons of health. Deficiency is especially common for athletes at higher latitudes who participate in indoor sports during the winter months. These conditions lead to limited sun exposure and thus and a paucity of vitamin D synthesis. While there’s no universal agreement on what “deficiency” means, the Endocrine Society recommends that 25(OH)D levels should be above 30 ng/mL (75 nmol/L), although worldwide recommendations for preventing rickets provide lower cutoffs. Some researchers even argue that optimal levels for athletes should be 40 ng/mL (100 nmol/L). Regardless of the specifics, it seems that athletes living further away from the earth’s equator could use a little more vitamin D, at least in the winter months.
The question is: how much do they need? And would supplementation actually have an effect on athletic performance? After all, just because vitamin D influences muscle cells, dietary supplementation may not necessarily translate to improved performance. While there have been several small trials looking at this issue, they haven’t led to firm conclusions, in part due to their small sample sizes. The study under review is the first meta-analysis attempting to synthesize them to answer these questions.
Vitamin D affects practically every tissue in the body. In muscle, it leads to the transcription of genes that affect muscle development and function. Since many athletes are vitamin D-deficient, this raises the question of how much supplementation athletes need to get their levels up and whether this would have any effect on athletic performance.
Other Articles in Issue #37 (November 2017)
Interview: Matt Stranberg, MA, RD, CSCS
In this interview, we chat with Matt about the utility of personal genomics for nutrition, how to keep up with nutrition research, what leads to successful dieting, and much more.
Interview: Mike Howard
Personal trainer and mindset performance coach Mike Howard shares his wisdom on how to stick with goals, his thoughts on Whole30, and more.
Aspartic acid on trial: no, it doesn’t boost testosterone
The evidence for D-aspartic acid boosting testosterone has been mixed. This trial used a high dose for a longer time to help settle the matter.
A whole (grain) in the evidence
Whole grain is thought to be heart healthy, mainly because of observational evidence. Are randomized controlled trials consistent with this recommendation?
Can riboflavin reduce muscle soreness?
Most research on riboflavin in athletics has focused on its effects on performance. Its effect on recovery are less well studied.
Can magnesium supplementation reduce cardiovascular disease risk factors in people with diabetes?
Observational, mechanistic, and animal evidence suggests that magnesium deficiency could raise the risk of CVD and diabetes. Could supplementation help?
Is exercise enough to improve the metabolic syndrome?
Diet and exercise combined can make an impact on factors of the metabolic syndrome. But could exercise by itself be enough to make a meaningful improvement?