- Observational studies have previously suggested that vitamin D supplementation may help muscle health.
- However, in a new meta-analysis, researchers have found that vitamin D supplementation shows no signs of improving muscle health.
- Furthermore, people taking vitamin D supplements performed worse on some measures than those taking a placebo.
In a new meta-analysis, researchers have found that taking vitamin D supplements does not benefit muscle health.
Additionally, the scientists discovered that on some measures, vitamin D supplementation reduced muscle health relative to placebo.
The study, which appears in the Journal of Bone and Mineral Research, provides valuable, high quality evidence on a topic that has previously shown mixed findings.
Vitamin D
According to the National Institutes of Health Office of Dietary Supplements, vitamin D is important for healthy bone growth. It also plays a role in reducing inflammation and affects cell growth, glucose metabolism, and the immune system.
Our bodies synthesize vitamin D following direct exposure to sunlight. Some foods also contain vitamin D, including fatty fish and fish oils, eggs, and mushrooms exposed to ultraviolet light.
In a study drawing on data in the United States between 2011 and 2014, researchers found that 5% of people over the age of 1 year in the U.S. were at risk of vitamin D deficiency, while 18.3% were at risk of vitamin D inadequacy.
Speaking on a podcast of the Endocrine Society, Dr. Laurel Mohrmann and Dr. Sweta Chekuri, both of Montefiore Medical Center, New York City, say that a key reason for vitamin D deficiency is people not getting enough sunlight exposure at great enough strengths.
“The amount of sun exposure that you get is the biggest player because natural sources of vitamin D in food are very rare. You don’t really get it from your diet, so you have to be exposed to sunlight.”
“In our country, a lot of our population lives far above the equator, so there’s less sunlight exposure from that, and there’s prolonged winter periods with very low sunlight exposures.”
“People with darker skin, older age, higher [body mass index] — all of these things are associated with vitamin D deficiency.”
“One other thing is as a nation, we have started supplementing our milk with vitamin D. As other forms of milk, such as soy milk and almond milk, get more popular, they’re not supplemented with vitamin D, so that source that was added into our diet to combat vitamin D deficiency is no longer being consumed by a large portion of the population,” says Dr. Morhmann.
Recently, researchers have been looking at vitamin D supplementation to see if it is protective against COVID-19. However, in an editorial for the BMJ, researchers highlighted there is limited research on the link between vitamin D and COVID-19. Furthermore, the evidence that does exist is contradictory on whether vitamin D is beneficial or not.
One other area that researchers have investigated is the possible role vitamin D supplementation can play in improving muscle performance and health.
Speaking to Medical News Today, Dr. Lise Sofie Bislev, of the Aarhus University Hospital Department of Endocrinology and Internal Medicine, Aarhus, Denmark, and the corresponding author of the present study, highlighted that “vitamin D supplements have to a large extent been recommended to people complaining of muscle fatigue.”
However, researchers have noted that evidence for the effects of vitamin D on muscle performance and health has been mixed and limited by the demographics that studies have involved.
54 trials reviewed
To try and get more reliable information, Dr. Bislev and her co-authors conducted a meta-analysis of the available research.
The researchers only included double-blinded, placebo-controlled, English-language randomized controlled trials.
The team drew on data from 54 trials involving a total of 8,747 participants.
According to Dr. Bislev, their meta-analysis is important as it offers a rigorous overview of the current literature.
“Most previous meta-analyses report data on handgrip strength, the Timed Up and Go test, or a composite endpoint [such as] global muscle strength, with large variation between studies.”
“[Our] study reports effects on the ten most commonly reported outcomes in individuals treated with vitamin D2 or D3 as compared with placebo. Many of those endpoints have not previously been summarized in a meta-analysis. A large number of individuals were included, and the variation between studies [was] low.”
“Recently, two studies reporting beneficial effects of vitamin D on muscle strength — included in most previous meta-analyses — have been retracted due to scientific fraud. Furthermore, results from a large number of randomized clinical trials have recently been published emphasizing the importance [of] summariz[ing the] available data.”
No evidence of benefit
The researchers found no evidence of any benefit that vitamin D supplements provide for muscle strength and health.
Additionally, the team found that vitamin D supplements reduced muscle performance in the Timed Up and Go tests, the knee flexion tests, and the Short Physical Performance Battery tests.
Dr. Bislev said the negative results in the knee flexion tests could be due to the type and amount of vitamin D dose.
“For knee flexion, most included studies used daily dosages of vitamin D greater than 2,800 [international units], and it is possible that the harmful finding on this outcome is caused by the relatively high daily dose. We also speculate [that] high dose bolus therapy may play a negative role compared with low dose daily therapy.”
However, for Dr. Bislev, there may still be value in people with significant vitamin D deficiency taking a supplement for muscle strength.
“Most studies do not include individuals with low vitamin D levels, and no studies include individuals with severe vitamin D deficiency only. Therefore, we still need to investigate whether vitamin D may exert a beneficial effect in individuals with very low levels of vitamin D,” said Dr. Bislev.
According to Dr. Bislev, despite the negative results for some measures of muscle strength, this is not a reason that people should stop taking vitamin D supplements.
“In general, we need to interpret findings from observational studies — including findings in patients with COVID-19 — with caution. The main conclusion of our study is that vitamin D does not have a beneficial effect on muscle strength and may even have a small harmful effect.”
“Whether this small negative finding is of clinical relevance is unknown. People should not reconsider taking a low dose supplement to protect or treat osteoporosis, but given the enormous public interest in vitamin D, we need to be aware of the possible negative effects of mainly high doses of vitamin D.”
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