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The Missing Ingredient for Triathletes

By Monique Ryan

Vitamin D may turn out to be a wonder nutrient for triathletes. If you’re not getting enough —and you probably aren’t — you need to start. Scientists are increasingly looking at the so-called sunshine nutrient and finding it may not only help your bones and overall health. Getting the right dose, may make you a better triathlete.

The research on vitamin D and athletic performance is evolving. In 2009 the Journal of Clinical Endocrinology and Metabolism published a British study of 99 adolescent girls looking at the connection between nutrition and athletic performance using measures like jump height, speed and power. Going into the test, 70 percent of the girls had deficient levels of vitamin D in their blood. Those who had adequate levels of D generated more power and jumped higher and faster than girls with lower levels.

vitamin dIt was one of several recent studies that have hinted that getting enough vitamin D can provide a number of important functions for athletes such as increasing muscle power, boosting the immune system, decreasing inflammation and significantly lowering the risk of stress fractures.

The problem is that many of us aren’t getting nearly enough.

“We screen over 2,000 athletes per year and have found that 90–95 percent are vitamin D deficient,” said Bruce Hamilton, MD of the Qatar Orthopedic and Sports Medicine Hospital in Doha, who is conduction research on athletes and vitamin D.

Vitamin D is produced naturally in the skin when it’s exposed to UVB ultraviolet light; It’s also found in small quantities in food. But because of our indoor jobs and diligent use of sunscreen, and the weaker sun in the higher latitudes of the U.S., we’re getting much less than we should. “Every tissue in the body needs vitamin D, so if you are deficient, correcting this could affect performance,” said Robert Heaney, MD of Creighton University, and vitamin D researcher.  

The shortage in the general population is clear. In Dr. Heaney’s study of 1,179 Nebraskan women over the age of 55, two-thirds fell short of the vitamin D level considered optimal by many experts. But it’s not just middle-aged Nebraskans who falling short. Low levels have been found in groups from indoor athletes, like elite gymnasts, to cyclists who ride 16 hours a week outside. In a recent study of 20 distance runners in sunny Alabama, University of Wyoming dietitian and researcher Enette Larson-Meyer found 40-percent were too short on D.

That deficit may be hampering their performance. A recent study of the elderly found that the most vitamin-D-deficient in the group had the poorest walking speed, standing balance, and hand grip strength, while another study found that when a similar elderly group supplemented with vitamin D, they boosted the size, strength, and number of their fast-twitch muscle fibers. “This effect on muscle could have a huge impact on an 18-year-old sprinter if they experienced the same results,” said Hamilton, who plans to put that theory to the test with his own study.

There’s clearly room for more research on how vitamin D affects muscles and performance. But given the other wide-ranging and well-demonstrated health benefits of D — from heart health to cancer prevention — there’s no reason to delay getting your daily dose. “In view of the effects on bone health, the immune system and preventing inflammation, it makes sense to correct any deficiencies,” said Larson-Meyer.

Staying healthy during the winter months or during any time in the training season is important and vitamin D supports a strong immune system. “Vitamin D plays an important role in our innate immune system, which is our first line of defense against infections such as a cold. If your vitamin D status is compromised your early attack against pathogens could be greatly compromised,” said Dr. Bruce Hollis, professor of biochemistry at the Medical University of South Carolina. Persons with low vitamin D levels are 40-percent more likely to report respiratory infections such as colds or flu.

So how much D is enough? It depends on who you ask. In 2010 the Institute of Medicine (IOM) has released a long awaited report from an independent panel of scientists on Vitamin D recommendations. The new recommendations are likely to only further fuel the vitamin D story. While many researchers have called for a significant increase in vitamin D recommendations, the panel recommended an increase from the woefully low 200 IU to 600 IU daily for individuals aged 1 to 50 years.

Some researchers believe that even higher doses are appropriate. A 1999 American Journal of Clinical Nutrition review of vitamin D studies found that signs of toxicity have never been observed when a person takes less than 10,000 IU per day in supplement form; a daily dose of 50,000 IU has been shown to be toxic after several months. To put that in perspective, ten minutes in the sun produces 15,000 to 20,000 units — then the process essentially stops, naturally avoiding an overdose from sun exposure.

“The good news is that the panel recognized that people need more vitamin D, and it was a three-fold increase in the RDA. But the recommendations have not gone far enough, we still might be off by a factor of 2 or 3,” says Dr. Michael Holick, vitamin D researcher at Boston University. “They have also recognized that vitamin D is not as toxic as once thought, raising the Upper Limit from 2,000 to 4,000 IU.”

The reason for our poor vitamin D status is that humans evolved to efficiently and effectively absorb vitamin D from the sun through our skin and then convert it to the active form in our bodies. We can also effectively turn off vitamin D production from the sun when we have enough. But our diligent efforts at avoiding harmful rays to protect skin from aging and skin cancers, and effective use of sunscreen have impacted our vitamin D status, as does living in areas with limited direct sun exposure in the winter months. Adding to these veiled efforts are real limits with dietary intake. Unless you regularly consume wild-caught fish, most natural diets contain very little of this nutrient, and vitamin D fortified foods only play a supporting role in impacting our vitamin D status.

Sunlight is the most effective way to obtain vitamin D and the most controversial. Dermatologists advise that there is no safe sun exposure. “Even 10 to 15 minutes of unprotected sun exposure several times weekly can damage skin cells- which causes premature aging and could eventually lead to skin cancer,” says Dr. Debra Tanner Abell, a spokeswoman for the Skin Cancer Foundation. Only a few experts recommend sun exposure. “You can get 5 to 15 minutes of unfiltered sun two to three times weekly depending on your skin type, time of day, and time of year,” Holick says. “You can still protect your face, but your arms and legs should be exposed.” Lighter skinned individuals produce 10,000 to 20,000 IU of vitamin D in the summer in less than 30 minutes, while darker skinned individuals may require two to five times as much sun exposure.

A safer bet is to take a supplement. “Given the current data on vitamin D, it doesn’t seem wise to hold off on supplementing, though there are likely to be individual differences in how much each person requires,” says Edward Giovannucci, researcher and professor of nutrition at Harvard’s School of Public Health, “which is a good reason for getting tested.”

No one is saying to binge on vitamin D, or spend all summer roasting by the pool. “Super high levels of vitamin D won’t make your muscles function better,” says Dr. Larson-Meyer. Just make sure you’re getting enough.

What’s clear is that the sun is the fastest way to get vitamin D, and skin cancer or no, staying completely out of it will drive your D into the dirt — unless you’re diligently popping supplements. Larson-Meyer recently completed a study of 41 collegiate athletes at the University of Wyoming and found that in September, about 16 percent had insufficient or deficient levels of vitamin D. By February, that rate had grown to 64 percent, and by April—when the days of more direct sunlight returned—it was down to 20 percent. “In addition to this seasonal variation, we also found that insufficient and deficient levels were associated with a greater frequency of infectious illness, such as colds,” says Larson-Meyer.

Discuss having your vitamin D levels checked with your physician. If you do have low levels, you likely will be prescribed a therapeutic dose to raise levels to a more optimal range. A therapeutic dose of vitamin D should be monitored by a physician, with levels rechecked and a maintenance dose prescribed. The recent IOM report did also recommend that vitamin D tests need more standardization for accurate results.

How much you need to supplement can also vary with the time of year. Even if you plan on limited sun exposure from May to October, you should supplement in the other months if you live above 35-degrees latitude which is as far south as the northern tip of South Carolina, Oklahoma, and just north of Los Angeles. “Taking 1,000 to 2,000 IU per day, particularly in the winter months, makes sense,” says Dr. Giovannucci, “Since this brings us closer to natural levels without sun exposure.” For every 1,000 IU that you take from a supplement, you can increase your blood vitamin D levels another 10 ng/mL in three to four months.

For example, a triathlete found to have a serum 25 (OH)D level of 20 ng/mL would need to supplement 1,000 IU daily for 3 to 4 months to increase levels to 30 ng/dl. However, there can be individual differences in response, so retesting levels is helpful. A typical loading regimen prescribed by a physician includes 50,000 IU weekly for 8 to 16 weeks. Don’t take these amounts on your own, prolonged daily dosing at 10,000 IU or higher fo0r up to 10 weeks could potentially be toxic.

“We set the upper limit at 4,000 IU daily, which should maintain levels at 50 ng/ml. Going above this level may have chronic adverse effects,” says Dr. Joanne Monson, a member of the IOM Committee.

Supplements in the form of D3 are considered to be the most effective at raising vitamin D levels, while the D2 form favored by vegetarians may not be as potent. Check labels of multivitamins, calcium supplements, and individual vitamin D supplements for the form and amount.  Some multivitamins contain only 400 IU, while others now provide 800 to 1,000 IU. Cod liver oil is not recommended as a supplement as it contains high amounts of vitamin A and could lead to toxic doses.

Food sources of vitamin D are limited and listed below:

Halibut, Greenland, 3 oz — 932 IU
Salmon, fresh, wild caught, 3 oz — 619 IU
Mackerel, Atlantic, 3 oz — 547 IU
Shitake mushrooms, dried, 4 oz ­— 196 IU
Sardines, 3 oz — 164 IU
Tuna fish, 3 oz — 154 IU
Herring, Atlantic, 3 oz — 142 IU
Fortified milk, 1 cup — 98 IU
Egg, 1 — 25 IU

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Monique Ryan, MS, RD, CSSD, LDN is the leading endurance sports nutritionist. Her nearly 30 years of professional experience working with Olympic (consultant to USAT and USA Cycling), elite and age group endurance athletes and professional sports teams make her one of the most experienced and qualified sports nutritionists in the U.S. Ryan is founder of Chicago-based Personal Nutrition Designs and the best-selling author of Sports Nutrition for Endurance Athletes (3rd edition, VeloPress) and three other sports nutrition books. PND provides detailed nutrition plans for triathletes across North America competing in all race distances, with programs at  Ryan is a Certified Specialist in Sports Dietetics.