Friday, June 1, 2012

The Importance of Vitamin D

Most runners spend a good amount of time and effort focusing on our nutrition. We make sure that we consume protein and complex carbohydrates to rebuild muscle after a hard workout and we try to stay away from artificial ingredients and eat whole, natural foods to best fuel our runs. We hear a lot about Omega-3 fatty acids, antioxidants and the dangers of trans fats. Women, in particular, are often focused on getting enough calcium, either through diet or supplements, to promote bone health.

One key nutrient that often gets overlooked is Vitamin D. Vitamin D promotes calcium absorption and a deficiency can result in lower bone mineral density and an increased risk of bone loss or fracture. Vitamin D has even been linked to increased VO2Max, reduced inflammation (which means faster recovery) and improved immunity. Surprisingly, Vitamin D deficiency has become a worldwide epidemic but many go undiagnosed.

For runners, especially women, Vitamin D is especially important to preventing stress fractures. Many may remember when US marathon great Deena Kastor fractured her foot about 5K into the 2008 Olympic Marathon in Beijing. The cause? A Vitamin D deficiency. Recently, several of our runners have mentioned that their doctors discovered a Vitamin D deficiency after they experienced stress fractures or just general lack of normal energy.

So how do you make sure you are getting enough Vitamin D? Recommended Dietary Allowance (RDA) for children and adults ages 1-70 is 600 IU. Exposure to the sun stimulates the body to produce Vitamin D, but using sunscreen and even aging can hinder the body's ability to absorb the sun and produce the nutrient. Vitamin D is not found widely in foods, with the exception of fortified grains and fatty fish like salmon, tuna and fish oils:

Table 3: Selected Food Sources of Vitamin D [11]
FoodIUs per serving*Percent DV**
Cod liver oil, 1 tablespoon1,360340
Swordfish, cooked, 3 ounces566142
Salmon (sockeye), cooked, 3 ounces447112
Tuna fish, canned in water, drained, 3 ounces15439
Orange juice fortified with vitamin D, 1 cup (check product labels, as amount of added vitamin D varies)13734
Milk, nonfat, reduced fat, and whole, vitamin D-fortified, 1 cup115-12429-31
Yogurt, fortified with 20% of the DV for vitamin D, 6 ounces (more heavily fortified yogurts provide more of the DV)8020
Margarine, fortified, 1 tablespoon6015
Sardines, canned in oil, drained, 2 sardines4612
Liver, beef, cooked, 3 ounces4211
Egg, 1 large (vitamin D is found in yolk)4110
Ready-to-eat cereal, fortified with 10% of the DV for vitamin D, 0.75-1 cup (more heavily fortified cereals might provide more of the DV)4010
Cheese, Swiss, 1 ounce62

Make sure your multivitamin has sufficient Vitamin D (in addition to calcium), optimally, D3 (cholcalciferol), the most potent form of the vitamin. At your next physical, ask your primary care physician to check your Vitamin D levels- a simple blood test will indicate whether you are getting enough of this important piece of your training and overall health.

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