Physically Speaking Vitamin D
Vitamin D helps build strong bones, and is vitally important for a tennis player's health, training and performance. Vitamin D is a fat-soluble vitamin that is required for calcium regulation and bone health. Vitamin D also has a role in immune function, protein synthesis, cellular growth, inflammatory response, hormone synthesis and for optimal muscle performance and injury prevention. There are several different forms of vitamin D. Two types are important in humans: vitamin D2, which is made by plants, and vitamin D3, which is made by human skin when exposed to sunlight. Foods and supplements may be fortified with vitamin D2 or D3.
WHERE DOES VITAMIN D COME FROM?
- Ultraviolet-B-radiation (UVB): UVB is delivered to humans via the sun's rays. Vitamin D is unique in that the human body's needs can be met entirely through skin exposure to UVB.
- Dietary intake of Vitamin D: includes both D3 (animal form) and D2 (Plant form, such as fungi and yeast) which is derived from UVB exposure
- Ingestion of supplemental Vitamin D: Includes vitamin D supplements (eg USANA Vitamin D) intended to aid players in meeting their recommended vitamin D requirements (600IU per day). Players should consult a Sport Dietitian, Physician or other qualified medical professional before beginning vitamin D supplements.
RISK FACTORS FOR VITAMIN D INSUFFICIENCY AND DEFICIENCY:
- Indoor training such as gym work and practicing on indoor tennis courts.
- Dark (eg Africans) or extremely fair skin (eg Caucasians)
- Living and training at northern latitudes (greater than 35˚ - 37˚)
- Effective Sunscreen use that blocks UVB rays
- Low dietary Vitamin D intake
ASSESSMENT AND REFERENCES RANGES OF VITAMIN D:
In the blood, 25(OH) D concentration is the best indicator of Vitamin D status.
Reference values to assess Vitamin D status include: optimal (good amount), insufficiency (not enough), deficiency (lack of) and toxicity (Too much):
- Insufficiency = 20-30ng/mL (50-80nmol/L)
- Deficiency = < 20 ng/mL (50nmol/L)
- Sufficient = 31-39 ng/mL (80-100nmol/L)
- Optimal = >40 ng/mL (100nmol/L)
- Toxicity = >150 ng/mL (390nmol/L)
The optimal values allow vitamin D to be stored in the muscle and fat for further use in the body. 25(OH)D levels below 30ng/mL is a significant risk factor associated with stress fractures.
If you have a history of vitamin D deficiency and/or have one of the above risk factors see your physician. You should get tested for vitamin D levels (by a blood test), 1-2 times per year.
DAILY RECOMMENDATIONSFOR VITAMIN D:
Tennis players 14-50 years of age are recommended to obtain 600IU of Vitamin D per day. Regardless of dietary intake, 15 mins of unprotected sun exposure on 3-4 major body parts between the hours of 10am to 3pm provides approximately 10,000 to 20,000 IU for light skinned (eg Caucasian) individuals. This would take approximately 60 minutes for the tennis players with darker pigment in their skin (eg African) Production of Vitamin D from the sun is however affected by cloud cover, pollution, sunblock, skin pigment UV blocking clothes and age. Generally, a very SMALL amount of sun exposure on skin which is not covered by clothing or sunblock is required to get your daily dose of vitamin D.
VITAMIN D GUIDELINES:
Improving Vitamin D status can occur via: dietary sources, ultraviolet B exposure and supplementation. Lack of sun exposure appears to be the main risk factor for Vitamin D insufficiency. Sun protection factor (SPF) of 15 or more can decrease Vitamin D absorption. Therefore controlled sun exposure to UVB is needed. Safe sun exposure, especially in the summer months may help athletes to build up their vitamin D stores as the skin can synthesize about 10,000-20,000 IU of vitamin D in less than 30 min. However, if sunscreen (>SPF 15) or sunblock is used nearly 98% of UVB rays from the sun are effectively blocked and so is vitamin D synthesis. While there are clear contraindications to sun exposure in individuals with a history of skin cancer and melanoma, most individuals can benefit from 5-30 minutes of sun exposure several times per week. Sunlight should reach arms, legs, and trunk for greatest benefits. For dark, pigmented skin (African), up to 60 minutes of sun exposure may be needed to synthesize 10,000 IU/d of vitamin D. For fair skinned athletes (Caucasians), sun exposure of as little as 5 minutes can help synthesize vitamin D.
Foods containing significant levels of vitamin D naturally include:
- Salmon, sardines, tuna - 3oz/100g = 200-300IU
- Egg yolks - 2 = 50-80IU
- Fortified milk, soymilk & orange juice - 1 cup = 100IU
- Fortified cereals = 40-100IU.
The appropriate Vitamin D supplementation regime for tennis players depends on current 25(OH)D levels (determined by a blood test), the season and sun exposure. The WTA in partnership with USANA offers Full and Associate members vitamins, minerals and other nutritional supplements free of charge. USANA guarantees that products supplied to WTA players under their Athlete Guarantee Program are free of substances found on the WADA prohibited list. See a Sport Dietitian and/or Physician to discuss your vitamin D requirements. They can also provide guidance on your performance nutrition needs and the appropriate time for repeat blood tests.
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