As you continue to train and race for the remainder of the season, learning about your vitamin D status and focusing on your vitamin D intake from food and supplements might actually improve your performance. While there is limited data on vitamin D status in athletes, (let alone cyclists), some experts believe that poor vitamin D status can often be a problem among athletes, and affect your overall health and ability to train.
What it does
Vitamin D is unique from other vitamins. First, it is actually a hormone and unlike vitamins, which are derived from abundant food sources only, vitamin D can be synthesized from sunlight. In fact sunlight was our main source of vitamin D until recently and it is remains the best source (although not necessarily the safest), while food sources are very limited.
Most likely your first association with vitamin D is the important role in bone health and bone formation via calcium absorption, but it is now known to play numerous important roles in maintaining optimal health. Emerging data indicates that vitamin D deficiency is linked to chronic diseases such as hypertension, cardiovascular disease, diabetes, and certain cancers, as well as autoimmune diseases such as multiple sclerosis, lupus, rheumatoid arthritis, and inflammatory bowel disease.
Other functions of vitamin D more related to athletic performance, include the nutrient’s positive effect on the immune system. Hard training can increase incidence of upper respiratory infections and optimal vitamin D status could help prevent illness and infection. Vitamin D also plays a role in controlling inflammation, and vitamin D deficiency can increase risk of certain sports related injuries. There is some limited evidence that low vitamin D status is linked to suboptimal athletic performance and that correcting a deficiency could improve performance as related to muscle protein synthesis, neuromuscular function, and speed and endurance. While more research is definitely needed in regards to performance outcomes, it is appears reasonable that an athlete’s health and overall ability to train could be affected by suboptimal vitamin D status. Numerous studies by German and Russian scientists in the early 20th century suggest that vitamin D status might affect athletic performance. More specifically, these studies measured the effects of irradiation from a sunlamp and the associated improvement in athletic performance. Current research has focused on physical performance in the elderly, and that deficiency is associated with reduced muscle strength and poor physical function.
Are you deficient?
It is now estimated that vitamin D deficiency is an epidemic for all age groups in the United States and worldwide, though data on the vitamin D status of athletes is very limited. In fact, when your exposure to sun, or more specifically ultraviolet B (UVB) radiation is limited, this can compromise your vitamin D status. UVB rays stimulate the formation of the “pre-vitamin,” D3, in our skin, which is then converted to the active form that provides so many beneficial functions. You cannot receive toxic amounts of vitamin D from sunlight as excess pre-vitamin D3 is converted to other byproducts. However, with excessive sun exposure you can increase your risk of developing malignant forms of skin cancer from too much sun exposure.
Of course, many cyclists follow the current guidelines for wearing sunscreen when out training in the warmer and sunnier months, and consequently block the activation of vitamin D from sunlight, so even a cyclist training in Florida is at risk for deficiency. Other factors which can block vitamin D production include aging (synthesis is impaired), cloud cover and atmospheric pollution, skin pigmentation or melanin as darker skinned persons are at higher risk and need 10 times longer exposure to UVB rays to generate the same active vitamin D stores as lighter skin persons, clothing cover (reduced skin exposure), time of day (early and late in the day), and wintertime latitude of greater than 35 N (north of Atlanta, Georgia) or greater than 35 S (Auckland, New Zealand ) because of the low angle to the sun and inadequate UVB exposure.
Vitamin D Status
The inactive form of vitamin D, 25(OH)D, is the major blood form of vitamin D and is used as a clinical measure of vitamin D status because it provides a more stable measure than the active form 1,25(OH)D. Levels of 25(OH)D also reflect vitamin D produced from sunlight, as well as that obtained from food and supplement.
While exact blood levels of 25 (OH)D that define deficiency, insufficiency, and adequacy have not been agreed upon by all experts, less than 10 nanograms per decilitre (ng/dl) or 23 nanomoles per liter (nmol/L) is considered by most experts to be deficient. Levels of under 20 ng/dl or 50 nmol/L are considered insufficiency or marginal deficiency. At least 32 ng/dl and 75-80 nmol/L are needed to support optimal health and for disease prevention, though not all experts agree on these higher levels. Levels greater than 200 ng/ml or 500 nmol/L are considered potentially toxic.
Vitamin D deficient blood levels can be treated with high weekly doses of vitamin D as prescribed by a physician and then maintained with a daily dose after levels are rechecked. Many experts are now recommending 1,000 to 2,000 international units (IU) daily in the form of vitamin D3, which contrast with the current recommended levels in contrast with the current Daily Value for adults of 200 IU (ages 19-50) to 400IU (ages 51-70).
Good foods sources of vitamin D are scarce. The best sources are fatty fish such as salmon, tuna, and mackerel, and fish liver oils. Smaller amounts are found in beef liver, cheese, and egg yolks. Some mushrooms provide variable amounts of vitamin D. Fortified foods currently provide most of the vitamin D in the American diet. Fortified milk contains vitamin D, though sampling has indicated that some are under fortified. Cereals, soy milk, margarine, yogurt, and orange juice may also be fortified with vitamin D. Maximum levels of vitamin D added to food are specified by law, and consuming too much vitamin D is more likely to occur with over supplementation rather than food intake.
|Food||IU of vitamin D per serving|
|Cod Liver oil, 1 tablespoon||1,360 IU|
|Wild Salmon, 3.5 ounces||981 IU|
|Farmed Salmon, 3.5 ounces||249 IU|
|Mackerel cooked 3.5 ounces||345 IU|
|Canned Sardines, 1.75 ounces||250 IU|
|Cod, 3.5 ounces||80 IU|
|Milk fortified, 8 ounces||100 IU|
|Orange juice, fortified, 8 ounces||100 IU|
|Yogurt, fortified, 4-6 ounces||10-80 IU|
|Cereal, fortified, ¾ to 1 cup||40 IU|
|Egg yolk, 1||20 IU|
You can obtain supplements of D2 or D3, with D3 being considered the preferred form as it is three times more effective in raising vitamin D blood levels and maintaining those higher levels. Many multivitamins contain 400 IU, though some can provide 1,000 IU. Calcium supplements are often paired with 100 to 200 IU of vitamin D. Keep on top of your total vitamin D intake from regularly consumed foods and daily supplement intake and account for all sources. Do not exceed 2,000 IU daily unless advised to do so by a physician who is monitoring your vitamin D levels.
Because many factors affect UV radiation exposure and there is limited research, it is difficult to provide general guidelines for sun exposure. Some researchers suggest that 5 to 30 minutes of sun exposure between 10 am to 3 pm to the face, arms, legs, and back at least twice weekly would lead to sufficient vitamin D synthesis in light skinned persons, with longer exposure required for darker skinned persons. This exposure would not be sufficient from November to March at Northern latitudes.
Of course it is also advised to limit sun exposure as UV radiation is a carcinogen responsible for 1.5 million skin cancers that occur annually in the United States. Lifetime cumulative UV damage to skin is also largely responsible for age-related skin dryness and other cosmetic changes. It is not known for certain if there is a desirable level of regular sun exposure that imposes no or little risk for skin cancer.
In normal weight individuals vitamin D3 is stored in subcutaneous body fat and released as needed during the winter months. However, this process may be compromised in very overweight individuals as less vitamin D seems to be released from fat stores. Conversely, athletes with very low body fat levels could be at increased risk during the winter months because of less storage of vitamin D in fat tissues, though this has not been measured.
Because vitamin D plays important roles in bone health, chronic disease prevention, and in inflammation and immunity, it is recommended that vitamin D status be measured and appropriate food and supplement intake implemented as needed. Improving the status of vitamin D deficient athletes, particularly those with the lowest levels, may improve athletic performance.
Monique Ryan, MS, RD, LDN is a nationally recognized nutritionist with over twenty-four years of experience and is owner of Personal Nutrition Designs, a Chicago based nutrition consulting company that provides nutrition programs for endurance athletes across North America (www.moniqueryan.com).