Like most people, I spent several hours of the past weekend perusing PubMed, this time reviewing some older studies on vitamin D. An interesting study from 2005 published in the journal Cerebrovascular Diseases from Switzerland caught my attention for a couple of reasons. First, the findings showed that vitamin D supplementation could reduce falls and fractures in elderly women after a stroke—but more significant was how it reduced falls. Second, the study reminded me of a conversation I had with one of the leading experts in functional medicine in which he expressed his concern over practitioners’ reticence to develop their own reasonable nutritional protocols.
This double-blind placebo-controlled study followed 96 vitamin D-deficient elderly women for two years after they had suffered a stroke. Half were given 1,000 IU per day of vitamin D and half received a placebo. The researchers examined the frequency of falls and fractures but also looked at number and size of type II muscle fibers—naturally this is what sparked my increased interest.
Type II fibers are the fast-twitch fibers and they are more responsive to hypertrophy. This study found that the women who supplemented with vitamin D increased the “relative number and size of type II muscle fibers and improved muscle strength.” The conclusion of the researchers was that women suffering from atrophy and vitamin D deficiency could reduce their number of falls and fractures simply by supplementing with 1,000 IU of vitamin D. They also stated that vitamin D supplementation could increase muscle fiber size and number. Let me say that this study did not suggest that vitamin D supplementation would give us all huge biceps and massive bench presses and I would obviously agree.
But like anyone with a curious mind, I study the research and consider how I can apply it to what I do—specifically, is there an application for this information in improving health, athletic performance, muscle size, and/or fat loss? While this study does not directly address those questions, I see a definite connection to what I teach. My broader conclusion to the above trial is that it’s possible that vitamin D deficiency may in fact hinder optimal muscle size and function. Said another way, if a client is training for more powerful muscle contractions and consequently more muscle growth, it is quite possible that vitamin D deficiency or insufficiency may be holding them back from maximizing their potential.
My clinical takeaway is that this is just one more reason to be sure that all of my clients—and myself and my loved ones—achieve optimal vitamin D levels and maintain them at all times. Since we’re now going into the winter months and most of us are living at a latitude where we can no longer count on getting any vitamin D from the sun, we should be supplementing with between 2,000 to 5,000 IUs per day.
Indeed, there’s evidence that athletic performance is seasonal with peak performance occurring during late summer, with a sharp decline in autumn and poorest performances coming during the winter. Researchers have suggested that fluctuations in vitamin D levels may be a cause. One case study of a 36-year-old recreational athlete in year-round training found that he had an increase in the maximum number of pushups in the late summer followed by a rapid decline in the fall and lowest performance in the winter despite continued training. Researchers suggested the reason was “seasonal variations in an unidentified hormone”—remember that vitamin D is actually a steroid hormone, not an enzyme or antioxidant like other vitamins. A second study of ten elite Swedish runners found they had the highest maximal oxygen uptake during the summer with oxygen uptake gradually decreasing throughout the winter until May when it began to increase.
It is unproven that seasonal fluctuations in vitamin D levels are the source of these variations in athletic performance, but I wouldn’t rule vitamin D out as at least a contributing factor. Perhaps more convincing is data demonstrating vitamin D’s affect on muscle. Quadriceps muscle biopsies on 12 vitamin D-deficient individuals found atrophy of type II muscle fibers before treatment, with significant muscle growth and size after vitamin D supplementation. And, muscle biopsies of 11 individuals with osteoporosis, before and after administration of vitamin D together with 1000 mg of calcium a day for three months, showed significant increases in both the percentage and area of type II fibers despite the lack of any physical training. Participants also had increases in creatine phosphate and ATP stores, both of which were low at baseline.
It’s highly likely that adequate vitamin D has some positive effect on muscle size and strength, and vitamin D plays such an essential role in maintaining health that the European Journal of Clinical Nutrition devoted the entire September issue to new research on it. In fact, the edition included a review that estimated that doubling the world population’s vitamin D levels would result in a 20 percent drop in mortality rates from diseases related to vitamin D deficiency. Researchers suggest vitamin D therapy as a preventative strategy that can lower rates of leading disease killers including cardiovascular disease, various cancers, type II diabetes, Alzheimer’s, osteoporosis, and severe upper respiratory disease. Additionally, if the world population doubled its vitamin D intake, the direct economic burden of disease could be reduced by 10 percent.
Then, I recall a recent study that may have more application to my work of coaching optimal health and peak performance. In one team of 89 NFL players, 27 were vitamin D deficient and another 45 players had insufficient vitamin D levels. That’s 80 percent of the team with subpar vitamin D levels—called an “alarming percentage” by researchers. But, what particularly grabbed my attention was that the athletes with lower vitamin D had a higher injury rate! Sixteen athletes suffered a muscle injury over the previous season, and the injured athletes had an average vitamin D level of 19.9 ng/ml, which would be considered “deficient.”
Even though the specific mechanism by which vitamin D plays a role in maintaining muscular health is unclear—does vitamin D improve muscle growth and power, or does adequate vitamin D simply protect against injuries and decreases in muscle growth and power?—this evidence raises the value of adequate vitamin D levels. There’s no doubt in my mind that keeping an athlete healthy and avoiding injury is critical for enabling the best performance possible.
I should also mention that there’s ample evidence that race and skin tone significantly affect vitamin D levels, with blacks and individuals with darker skin tone typically having lower levels. In the study of NFL football players, the black players as a group had deficient vitamin D levels that averaged 20.4 ng/ml, which were 10 points lower than the white players. These findings are not unique to this study. For example, a 2010 study found that 93 percent of blacks and 70 percent of whites were vitamin D deficient with serum levels below 30 ng/ml. Researchers identify skin color, diet, demographic region, and body mass index to all play a role in vitamin D levels. They suggest that everyone needs to supplement, while darker skinned individuals and those who aren’t exposed to daily sunlight need to take more.
If you’re not seeing the strength and muscle gains you’d expect from your training, low vitamin D levels could be one reason, and it is an easy variable to remove. If I’m wrong, the worst case scenario is that by achieving optimal vitamin D levels you will have reduced your risk of a muscle injury or of developing various diseases like osteoporosis, cancer, diabetes, depression and more. No downside to taking more vitamin D—all upside.
This observation is what led me to my other reason for highlighting this study—too many practitioners are afraid to make their own conclusions, and instead, rely solely on the conclusions of the peer-reviewed literature. Like my functional medicine expert friend stated, our practitioners need to give themselves more credit for being able to come to logical conclusions and create intelligent nutritional protocols for their patients and clients. While I may not have proof that vitamin D will help all my athletes, I do have a plethora of research studies that suggest it may help, and I can recommend this to my clients with absolute confidence that
1) I won’t make them worse—a.k.a., do no harm,
2)I will be helping them reduce their risk of injury and of many, many diseases—a.k.a. the “side effects” and
3) I may greatly improve their results as it relates to their strength, muscle size, and therefore fat loss.
If I relied solely on the research conclusion, I would only have considered adding vitamin D if my client was an elderly female who had recently suffered a stroke and did not want to fall down—oh, and by the way—that’s another good reason to use vitamin D.
Sato, Y., Iwamoto, J., Kanoko, T., Satoh, K. Low-Dose Vitamin D Prevents Muscular Atrophy and Reduces Falls and Hip Fractures in Women after Stroke: A Randomized Controlled Trial. Cerebrovascular Disease. 2005.
Shindle, M., Voos, J., et al. Vitamin D Status in a Professional American Football Team. The American Orthopedic Society for Sports Medicine Annual Meeting. 2011.
Signorello, L., Williams, S., et al. Blood Vitamin D Levels in Relation to Genetic Estimation of African Ancestry. Cancer Epidemiological Biomarkers Preview. September 2010. 19(9), 2352.
Kittles, Rick. Disparities in Vitamin D Levels: Gene X Environment Interactions. American Association of Cancer Research Fourth Annual Health Disparities Conference. September 2011.
Cannell, J., Hollis, B., et al. Athletic Performance and Vitamin D. Medicine and Science in Sport and Exercise. May 2009. 41(5), 1102-1110.
Grant, WB. An Estimate of the Global Reduction in Mortality Rates Through Doubling Vitamin D Levels. European Journal of Clinical Nutrition. September 2011. 65, 1016-1026.
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Young, A., Edwards, R., et al. Quadriceps Muscle Strength and Fiber Size During Treatment of Osteomalacia. Mechanical Factors and the Skeleton. London: John Libbey. 1981. 12, 137-145.
Sorensen, O., Lund, B., et al. Myopathy in Bone Loss of Ageing: Improvement by Treatment with I Alpha-Hydroxycholecalciferol and Calcium. Clinical Science (London). 1979. 56(2), 157-161.