Vitamin D

Vitamin D is a fat soluble vitamin and it is obtained from sunlight, diet and supplementation, and plays an important role in bone health, gene expression and cell growth.

Published September 18, 2013 12:00

Vitamin D
Milk is a good source of Vitamin D

Vitamin D is a fat soluble vitamin and it is obtained from sunlight, diet and supplementation. There are two different forms of Vitamin D, D3 (cholecalciferol) formed in the skin and is found in most vitamin D supplements and D2 (ergocalciferol) which is found in a limited amounts of food. This vitamin plays an important role in bone health, gene expression and cell growth. Recent research is showing a relationship between vitamin D and muscle strength and function. Both forms of vitamin D are converted in the liver to 1, 25-hydroxyvitamin D (25(OH)D) which is the main circulating form and the best indicator of vitamin D status.

What is Vitamin D deficiency?
Through a blood test serum levels of (25(OH)D) can be determined.

• Vitamin D deficiency = serum levels ,20ng/ml (50nmol/L)
• Vitamin D insufficiency = 30ng/ml (75nmol/L)
• Vitamin D sufficiency = 30ng/ml (75nmol/L)

The ideal range is 75-120 nmol/L

Which athletes are at risk of vitamin D deficiency?
• Those that train and compete indoors
• Competitors for the Winter sport
• Have dark skin pigmentation
• Live at latitudes >35 degrees north or south of the equator
• Cover up for sun safety, cultural or religious reasons
• Family history

What are the signs and symptoms of Vitamin D deficiency in athletes?
• Low bone mass score (Z score > -1 for spine or proximal femur)
• Bony injury such as stress fractures
• Bone softening (osteomalacia) due to poor mineralization of bone
• Chronic Fatigue
• Muscle and joint pain

Dietary sources:
Small amounts of vitamin D can be found in food such as oily fish, egg yolks and fortified foods such as milk, orange juice etc. The daily requirements for adult women (19-70years) are 600IU/15ug per day. Diet alone will not provide sufficient vitamin D for your daily needs.
What kind of Vitamin D Supplement is suitable for purchase?
Vitamin D3 is the preferable supplement form and a daily dose of 400IU per day is suitable for prevention. To raise serum levels to greater than 30ng/ml (75nmol/L), daily doses of 1000-2000IU per day is required to be taken for 6-12 weeks and then re-test.

Sunlight Exposure:
The principle source of vitamin D comes from exposure to ultraviolet B (UVB) radiation from sunlight. Optimal sunlight exposure in the summer is 10-15 minutes per day, 3-4 times per week. It is necessary to get exposure on 2 parts of the body e.g. legs, arms, back. Longer times are required for darker skins (3-6 times more) and seasonal variation. Sunscreen needs to be applied adequately after vitamin D exposure is completed.

Can too much Vitamin D be harmful?
Vitamin D is a fat soluble vitamin and when amounts become too high signs of toxicity can occur e.g. nausea, vomiting, poor appetite, weakness and weight loss. It is well known that prolonged exposure to the sun can have adverse effects on the skin and thus safe sun exposure is essential. Vitamin D supplements can also interact with certain medicines (e.g. corticosteroid medication) so always inform your doctor that you are supplementing with vitamin D.

Thanks to Susie Parker Simmons, MS, RD, MED
Sports Dietician and Physiologist
WTA Sports Nutrition Advisor


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