In former observational studies, they suggest that supplementing with vitamin D can actually aid in muscle health. But in a recent meta-analysis, a research team has found that vitamin D supplementation actually ‘shows no signs of improving muscle health.’
Moreover, individuals that took vitamin D actually did worse in certain activities, having diminished muscle health, than those that were given placebo.
Appearing in the Journal of Bone and Mineral Research, the study gives a beneficial and relevant look into the topic of vitamin D.
What is Vitamin D?
In the National Institutes of Health Office of Dietary Supplements, it shares that healthy bone growth requires vitamin D. They also share how it plays a vital role in lessening inflammation, while also positively affecting glucose metabolism, cell growth, as well as the immune system.
The body synthesizes vitamin D right after it has had direct exposure to sunlight. But people can also get vitamin D from particular foods such as eggs, fish oils, fatty oils, and mushrooms that have been exposed to ultraviolet light.
In a study conducted in the United States that took data from the years 2011 to 2014, the study authors 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.’
The Endocrine Society shared a podcast with Dr. Laurel Mohrmann and Dr. Sweta Chekuri from the Montefiore Medical Center in New York City. They explained that one main reason why people tend to have vitamin D deficiencies is because they don’t have enough exposure to sunlight, and at great enough strengths from the sun at that.
Dr. Morhmann explained, “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 addition, she said, “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,” she added.
Furthermore, in recent studies, researchers have been looking into vitamin D supplements as ways to help prevent against Covid-19. But an editorial published in BMJ explains that there is still a lack of research on the link between Covid-19 and vitamin D. Meanwhile, any evidence that was found is actually conflicting on whether supplementation of vitamin D is truly helpful or not.
In addition, research teams have looked into vitamin D supplementation and the role it plays in improving muscle health and performance.
In light of this, Dr. Lise Sofie Bislev from the Aarhus University Hospital Department of Endocrinology and Internal Medicine in Aarhus, Denmark, and also lead author of the present study, spoke to the publication Medical News Today, saying “vitamin D supplements have to a large extent been recommended to people complaining of muscle fatigue.”
Yet the researchers also note that the findings on the effects of vitamin D on muscle performance and health show mixed results, partially due to the mixed and limited demographics of the studies that were done on the subject.
Reviewing 54 Trials
In order to get dependable information on the topic, alongside her co-authors, Dr. Bislev conducted a meta-analysis of the research that is already available on vitamin D.
The study included ‘double-blinded, placebo-controlled, English-language randomized controlled trials.’ And they took data from at least 54 trials that involved at least 8,747 participants.
Dr. Bislev explained how meta-analysis is important because it gives an accurate overview of the literature that is currently available.
She shared, “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.”
She went on to say, “[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,” she added.
There Was No Evidence of Benefits
Notably, the scientists found no evidence that vitamin D supplements benefit muscle strength and health in any way.
Moreover, the research team also found that vitamin D supplements actually reduced muscle performance in the ‘Timed Up and Go tests, the knee flexion tests, and the Short Physical Performance Battery tests.’
According to Dr. Bislev, she explained that the negative results that occurred when conducting the knee flexion tests could possibly be because of the kind and amount of vitamin D dose.
She explained, “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.”
But regardless of their findings, Dr. Bislev said that people taking vitamin D supplements for muscle strength could still benefit from them.
She said, “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.”
Dr. Bislev also said that while there were some negative results in the muscle strength measures, it isn’t a reason why people should stop consuming vitamin D supplements.
She shared, “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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