Sixteen years ago, Professor Walter Stumpf (who taught me at UNC School of Medicine) first made the case that vitamin D is intimately involved with sex and reproduction. Male genital tissue contains lots of vitamin D receptors but their significance and function remain unknown. One researcher actually gave a vitamin D-like-drug to see if it improved sexual performance in patients with renal failure! To bad for the instant popularity of vitamin D, the results showed no improvement.
Vitamin D does appear to improve virility. Conception peaks in the summer, when vitamin D levels are highest, and ebbs in the winter, when vitamin D stores are low. Vitamin D deficiency has profound effects on rat testicles, including dramatically reducing spermatogenesis. Vitamin D deficient male rats were 73% less likely to successfully father pups than vitamin D sufficient males. Vitamin D restored virility to vitamin D deficient male rats and should do the same for vitamin D deficient male humans.
What else are men interested in besides sex? Hair growth! In fact, hair follicles have large numbers of vitamin D receptors but their function is unknown. Although there are no human studies showing vitamin D will grow men a new head of hair, vitamin D like drugs do grow hair in mice. (By the way, both my wife and my barber have told me my head has stopped balding and I've kept my 25(OH)-vitamin D level around 50 ng/ml for several years.) One relevant animal study should get the attention of men; the title contains two of their favorite words: ?nude? and ?hair growth.?
What about weight? Can you see the headlines in the men's' fitness magazines: ?Vitamin D Reduces Weight.? Although dozens of studies have found that those with the highest 25(OH)-vitamin D blood levels weigh the least, most vitamin D scientists explain this by pointing out that vitamin D is stored in fat tissue, thus lowering blood levels. Of course that does not preclude vitamin D from also having either a direct or indirect effect on weight.
One study tried to answer that question by looking directly at vitamin D intake and body weight. The authors found an inverse correlation. That is, the more vitamin D in your diet, the less you weighed! If you have a few minutes, test your knowledge by taking our quiz on obesity and vitamin D.
Finally, we turn to athletic performance. After sex, hair growth, and obesity, improving athletic performance would certainly make American men pay attention to vitamin D. Actually, what we are asking is: ?Does the have any effects on balance, muscle strength, muscle mass, reaction time, etc?? When asked that way, it would be surprising if it had none. In fact, dozens of studies suggest vitamin D will improve athletic performance.
If vitamin D improves athletic performance, then we'd predict physical fitness should peak in the late summer when 25(OH)-vitamin D levels peak. The only two studies that looked at season of the year and athletic performance of trained athletes found physical fitness peaked exactly then.
Genetic ablation of vitamin D receptors caused profound impairment in the motor functions of mice. Furthermore, mice without the vitamin D receptor gene showed increased anxiety; performance anxiety is something all men want to avoid. Babies born to vitamin D deficient rats are permanently and irreversibly brain damaged, proving that vitamin D has profound effects on developing neural tissue. (We will have more on this important, and tragic, research coming out of Australia in a future newsletter.)
Muscle strength is important to athletes and it correlated with 25(OH)-vitamin D levels in older men. A vitamin D like drug improved muscle strength in vitamin D deficient older women. In fact, it did the same thing to a group of vitamin D deficient younger women. Furthermore, improved lower extremity function was directly associated with higher 25(OH)-vitamin D levels.
Athletes need to be quick. A single injection of 600,000-units of vitamin D significantly improved reaction times in older adults. Furthermore, higher 25(OH)-vitamin D levels were also independently associated with better reaction time and better performance time.
Athletes need good balance. The beneficial effect vitamin D has on balance (reduced falls) is not limited to profoundly vitamin D deficient populations; a vitamin D-like-drug improved balance in the general elder population, even those with ?normal? 25(OH)-vitamin D levels. A more recent study showed higher 25(OH)-vitamin D levels correlated with better gait speed, balance and muscle strength.
Vitamin D also appears to maintain muscle mass in older people but, no one has reported similar studies of young adults. A recent review concluded that vitamin D is an authentic strength preserving hormone, at least in the elderly. There is no reason to think it has any less effect on vitamin D deficient younger persons.
Finally, debilitating chronic pain sidelines many athletes. One Mayo clinic study found that virtually all patients treated for chronic pain have low 25(OH)-vitamin D levels. Furthermore, in what must be one of the largest open studies ever reported, 360 patients with low back pain in Saudi Arabia responded exceptionally well to treatment with physiological doses of vitamin D. Like virtually all areas of vitamin D research, we are still awaiting definitive research.
An impressive scientific literature suggests that vitamin D may improve athletic performance. This should surprise no one as other steroid hormone systems improve athletic performance. One difference is that the U.S. government is going to find it hard to regulate the vitamin D steroid hormone system; the sun is both a free and robust source of vitamin D. Of course, oral vitamin D is toxic in overdose and vitamin D toxicity would greatly impair athletic performance. Smart athletes would get enough sun, or take enough cholecalciferol, to keep their 25(OH)-vitamin D levels around 50 ng/ml, year around. But then, smart non-athletes would do the same.
What would happen if researchers gave physiological doses of cholecalciferol to men for a year or two and studied their sex life, hair growth, weight and athletic performance? Would vitamin D improve men's sex life? Would it make them more virile? Would they stop going bald? Would they lose weight? Would they become better athletes?
We don't know. However, a rapidly expanding scientific literature indicates vitamin D lowers their risk of heart disease, diabetes, hypertension, multiple sclerosis, autoimmune illness, depression and seventeen different types of cancer. It now appears likely that vitamin D has an important role in treating those killer diseases as well.
But that doesn't really interest most American men. Men want to know about the important stuff. Why not start taking 2,000 units of cholecalciferol every day and see if your sex life improves, your hair grows back, you lose weight, and you become a better athlete? (And, don't forget to measure down there; after all, you never know).
John Cannell, MD
The Vitamin D Council
9100 San Gregorio Road
Atascadero, CA 93422