New studies find that Vitamin D may be more important than previously thought when it comes to the health of endurance athletes.
Written by: Nathan Koch
As an avid cyclist and runner, I am always looking for ways to improve performance while avoiding forced time off due to injury or illness. While attending the American College of Sports Medicine meeting in Seattle last year, I heard a lecture from a well-known researcher on the benefits of vitamin D supplementation, which included increased athletic performance. I even learned about a study in which Russian and German athletes used ultraviolet sunlamps to improve performance. Four Russian sprinters used UV light and another group didn’t. The two groups trained identically for the 100-meter sprint. The control group lowered its time by 1.7 percent and the UV group improved 7.4 percent.
A more recent study from the University of Wyoming’s family and consumer science department revealed a direct correlation between vertical leap height (think power) and vitamin D levels.
So, of course, at my next physical, I asked my physician to order a vitamin D blood test (serum 25[OH]D concentration) along with the other standard tests. As a healthy endurance athlete residing in sunny Arizona and training outside on a daily basis, I was shocked by my results, which were 25nmol/L. My physician said that if my levels were any lower I would qualify for aggressive treatment. For the record, maintaining blood concentrations above 80nmol/L is currently considered ideal by most of the literature, although more research is needed.
Vitamin D deficiency is a growing epidemic in the U.S. and throughout the world. The deficiency causes rickets in children, osteoporosis in adults and stress fractures in athletes and has been linked to cancer, cardiovascular disease, multiple sclerosis, rheumatoid arthritis, type-1 diabetes mellitus and even influenza.
Vitamin D (calciferol) is really a combination of cholecalciferol (vitamin D3) and ergocalciferol (D2). D3 is produced by the action of ultraviolet B light on the skin of humans and is found in oily fish. D2 is formed when ultraviolet light irradiates the fungal steroid ergosterol, and very little is found in our food. With few exceptions (see table 1) there is little or no vitamin D in the food people normally eat. In other words, vitamin D deficiency is less a nutritional issue and more an environmental deficit due to inadequate ultraviolet exposure. In the past, most experts thought we could get enough vitamin D from fortified milk, but today there is increasing agreement among researchers that this measure does not even come close to doing the job.
Vitamin D absorption from the sun also has limitations and is affected by latitude, season of the year, time of day, skin pigmentation, use of sun block, age and clothing. Optimal sun exposure typically occurs between 10 a.m. and 3 p.m. and at lower latitudes. Therefore, those of us who live in the northern half of the U.S. or anywhere in Canada or Europe are at risk of being deficient. Whereas our ancestors were exposed to the sun almost daily, today we allow less than 5 percent of our skin to be exposed to sunlight. We work, play and live under artificial light, and when we get the time to soak up some rays, we either block the beneficial rays with high-powered sunscreen or totally overexpose ourselves, turning ourselves into tomatoes.
In athletes, a vitamin D deficiency can cause the dreaded down time resulting from a cold, the flu, stress fractures and joint inflammation. In a 2006 Finnish study on military recruits, Ruohola, et al., concluded that a lower level of serum 25(OH)D concentration may be a predisposing factor for bone stress fractures. Another study, from the University of Wyoming, found that 40 percent of a group of distance runners in Baton Rouge, La., were vitamin D deficient. For those of you who haven’t been to Baton Rouge, it is sunny and closer to ideal latitude for vitamin D absorption via skin than most other cities in the U.S. A recent and encouraging study by Lappe, et al., out of Creighton University, found a 21 percent lower incidence of stress fractures in female Naval recruits in a supplemented (vitamin D and calcium) group versus the control group.
So should we increase our sun exposure to guarantee vitamin D sufficiency and subsequently increase our risk of skin cancer? Or should we take supplements and hope that doing so is enough to prevent fractures and illness? As athletes, we know that life is a balancing act. Sometimes we can be extreme and have an all-or-nothing attitude, but this is one challenge that will take a comprehensive approach and require careful moderation.
My everything in moderation theory for optimizing vitamin D efficiency:
1. Monitor your serum 24(OH)D levels with help from your physician. Test in the summer and in the winter.
2. Increase dietary and supplemental vitamin D2 and D3. Again, consult your physician for the specific amount. Remember the recommended daily allowance is low (400 IU) and not up to current research standards. At least 1,000-2,000 IU vitamin D3 per day is considered the new minimum. Recent research demonstrates these levels are safe and effective.
3. Get direct sun exposure for 10 to 30 minutes a couple of times per week. Sensible sun exposure is the most natural and effective way to increase vitamin D levels.
4. If all the above fail, move closer to the equator, surf some waves, eat some fish and do some shots of cod liver oil.
Here’s a list of Vitamin D-rich foods from the National Institutes of Health:
Cod liver oil, 1 tablespoon
Mushrooms, enriched with vitamin D, 3 ounces
Salmon, cooked, 3.5 ounces
Mackerel, cooked, 3.5 ounces
Sardines, canned in oil, drained, 1.75 ounces
Tuna, canned in oil, 3 ounces
Orange juice fortified with vitamin D, 1 cup (check product labels, as amount of added vitamin D varies)
Milk, nonfat, reduced fat, and whole, vitamin D-fortified, 1 cup
Yogurt, fortified with 20 percent of the daily value for vitamin D, 6 ounces (more heavily fortified yogurts provide more of the daily value)
Margarine, fortified, 1 tablespoon
Ready-to-eat cereal, fortified with 10 percent of the daily value for vitamin D, 0.75-1 cup (more heavily fortified cereals might provide more of the daily value)
Egg, 1 whole (vitamin D is found in yolk)
Liver, beef, cooked, 3.5 ounces
Swiss Cheese, 1 ounce