Because vitamin D plays a role in numerous physiological functions including gene modulation, immune function, protein synthesis and calcium absorption, it is likely a key to maximizing athletic performance. Muscle pain and weakness which occur in diseases such as rickets (the weakening and softening of bones in children, usually because of significant and long-term vitamin D deficiency) have been shown to subside with supplementation of vitamin D. There are few studies that demonstrate the direct relationship between vitamin D status and performance of athletes. However, there are studies that show improvement in aerobic fitness, jump height, velocity and power among individuals who are not athletes, but known to be deficient in vitamin D.

Vitamin D can be obtained not only from food sources, but also from exposure to sunlight. Production of vitamin D from sunlight depends on time of exposure, season, latitude, cloud cover, smog, skin pigmentation, age and sunscreen use. Unfortunately, in the winter months, it cannot be synthesized in latitudes greater than 35⁰ and 37⁰ north or south. (Chicago is located between 41⁰ and 47⁰ degrees north.)

Good dietary sources of vitamin D include egg yolks (25 IU), fatty-fish such as tuna (154 IU for 3 oz canned), salmon (794 IU, sockeye, 3 oz), sardines (46 IU for 2, canned in oil) and mackerel (388 IU, 3 oz cooked), breakfast cereal (40 IU for about 1 cup), irradiated mushrooms (400 IU for 3 oz), yogurt, fortified milk (120 IU in 1 cup), some brands of margarine (60 IU, 1 tablespoon), and fortified orange juice (100 IU in 1 cup).

From birth to the age of 50, individuals need 200 IU of vitamin D per day. Individuals aged 51-71 need 400 IU per day, and those over the age of 71 need 600 IU per day.

Dietary Fact Sheet: Vitamin D (http://ods.od.nih.gov/factsheets/VitaminD/)