If you train hard and seek maximum results, you need vitamin D. Although the body can make it when the skin is exposed to sunlight (by converting cholesterol to vitamin D), this mechanism depends greatly on the season and your sunbathing habits. Beyond sun exposure, vitamin D is found in fortified dairy products, fatty fish (salmon, mackerel) and cod liver oil.
It’s been known for years that vitamin D is intimately involved in calcium handling, bone metabolism and neuromuscular function. However, the latest research shows that it does much more. Recent interest in vitamin D supplementation for athletes has been triggered by data showing that muscle tissue contains vitamin D receptors that are involved in strength and growth. What’s more, it has been suggested that most athletes are vitamin-D deficient, especially in the winter months, because of inadequate sun exposure combined with low-variety diets.
Signs of Deficiency: Individuals who are vitamin-D deficient often complain of tiredness, overall weakness and muscle aches. Because these signs can indicate many problems, your best bet is to take a blood test for 25-hydroxyvitamin D, which can be done through your family physician or by purchasing an online test kit.
Supplementing With D: If you’re an athlete and you tend to avoid sun exposure, you are likely vitamin-D deficient. Supplement recommendations vary, but the daily upper limit of vitamin D intake in adults is generally reported as 2,000 IU. That said, studies in athletes have shown that up to 10,000 IU per day is safe, well-tolerated and beneficial.