Vitamin D

Vitamin D deficiency is becoming an epidemic worldwide, not only in geographic regions where sun exposure is limited. Moreover, vitamin D increases the number of type II or fast twitch muscle cells urthermore, vitamin D supplementation in young males with low vitamin D levels increases the percentage of type IIA fibers in muscles, causing an increase in muscular high power output.

Vitamin D levels are strongly associated with exercise performance in athletes and physically active individuals. In the elderly and in adults below the age of 65, several studies have established a close association between vitamin D levels and neuromuscular coordination.

Athletes who live in northern latitudes (north of 35 degrees), or use sunscreen consistently, perform their sport indoors, or keep their skin covered are at the greatest risk. Melanin affects the production of Vitamin D. So those with more melanin, or darker skin, produce less Vitamin D.

Since Vitamin D is a fat-soluble vitamin, athletes with fat malabsorption problems such as cystic fibrosis, Crohn’s disease, and celiac disease are at risk for deficiency. Those who have normal levels typically (around 50 ng/ml) live in sub-equatorial Africa and work outdoors for most of the summer.

Once thought of as being primarily involved in bone development, activated Vitamin D (calcitriol), a steroid hormone, is responsible for regulating more than 1,000 human genes. Almost every cell in the human body has receptors for Vitamin D. Recent research shows that Vitamin D deficiency increases the risk of different types of cancer (such as breast cancer and prostate cancer), as well as heart disease, diabetes, depression, autoimmune diseases, hypertension, obesity, gum disease, chronic pain, muscle wasting, inflammation, birth defects, osteoporosis, influenza, colds, etc.

Importance for Endurance Athletes

We are only just beginning to understand the complexity and importance of Vitamin D in relation to health. Of importance to athletes is the function of Vitamin D as it relates to overall health, bone density, innate immunity, muscle wasting, and exercise-related inflammation and immunity. To train and race optimally, an athlete should not have any nutrient deficiencies.

Bone Health

Olympic Marathoner Deena Kastor broke her foot in Beijing during the 2008 Olympic Marathon. It was discovered that her calcium levels were normal, but her 25 (OH)D levels were reported to be around 15 ng/ml (Remember the goal is 50+ ng/ml. Kastor lived in sunny California. Because many parents and adults worry about skin cancer, many apply sunscreen for all of their outdoor runs and activities, thus limiting the ability to manufacture Vitamin D from sun exposure. Even with the extensive research to show Vitamin D and calcium’s role in preventing osteoporosis, elite, college, and high school athletes continue to be deficient in one or both nutrients. Stress fractures are quite prevalent in runners and yet so preventable.

Increased VO2 Max

German research studies dating back to the 1950s show that athletes exposed to Vitamin D-producing ultraviolet light had improved athletic performance. Other studies showed that athletic performance peaked at the end of the summer. Peak performance was also associated with 25 (OH)D levels around 50 ng/ml.

In addition, maximal oxygen uptake was found to drop when less ultraviolet rays reached the earth, for example, in the late fall. This is particularly a problem for marathoners training through the summer for fall marathons.

Reduced Inflammation

After intense exercise, endurance athletes experience inflammation due to elevated levels of pro-inflammatory cytokines. Vitamin D reduces the production of these cytokines while increasing the production of anti-inflammatory cytokines, thereby speeding the recovery process between hard workouts.

Improved Immunity

In a February 2009 study published in the Archives of Internal Medicine, Vitamin D3 levels were tested in 19,000 Americans. Those with low levels of Vitamin D had the highest incidence of colds and influenza. This is important information for endurance athletes who strive to balance heavy training loads and staying healthy.

What to Do Check

25(OH)D levels regularly and supplement as needed.

Total 25(OH)D reflects all sources of Vitamin D – from food, UV energy (photo production), and supplementation.

Deficient athletes measuring less than 30 ng/ml should work with MD but many will supplement with 20,000 IU to 50, 000 IU of vitamin D3 per week for eight weeks and recheck serum 25(OH)D until normal values are attained.

Get regular, safe, twice-daily (5-30 minutes) exposure to sun between the hours of 10 am and 3 pm. Note that sunscreen and glass (being indoors) reduce or block UV energy. Supplement with 1000 IU to 2000 IU of Vitamin D3 to maintain normal levels.

Food Sources of Vitamin D:

There aren’t many naturally occurring foods that contain vitamin D. Most of the foods containing Vitamin D have been fortified, for example milk and certain juices.

Table 1. Food Sources of Vitamin D

FOOD                               Serving                  IU per serving

Fish liver oils                    1TBSP                    1360

Herring, cooked                3 oz                        1383

Wild salmon, cooked        3.5 oz                      981

Farm salmon, cooked       3.5 oz                     249

Tuna, canned in oil           3.5 oz                     200

Milk                                   8 oz                        100

Margarine, fortified           1 TBSP                    60

Egg                                  1 whole                    18

Beef, liver                         3.5 oz                      15

Cheese                            1 oz                         12

*IU = International Units

**Remember to

1. Always plan ahead for what you are going to eat

2. Obtain adequate amounts of protein

3. Work on flexibility

4. Supplement your diet with a fish oil, a multi-vitamin

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