Exercise and vitamin D are both important for musculoskeletal health and bone health. Vitamin D may also have a beneficial effect on some types of cancer, in particular colorectal cancer, and other immune-related diseases. Skin exposure to UVB radiation from sunlight promotes vitamin D production in the skin. While outdoor exercise is the cause of higher vitamin D levels in runners, this effect is seasonal and is likely only seen in younger runners. Why? In Canada, for most of the winter months, there is insufficient UVB radiation from sunlight to have an effective amount of vitamin D production. Most Canadians do not get enough dietary vitamin D. It is found in the skin of fatty fish, some mushrooms, fluid milk, soy beverages, and some yogurts. Unless you are eating and drinking these foods daily, you likely are not meeting your needs for vitamin D from foods. Skin cells get old too – and the skin’s production of vitamin D decreases with aging. 50 years of age seems to be the cut-off.
Which runners are at greatest risk for inadequate vitamin D?
Older runners (> 50 yrs) - as one ages, there is reduced production of vitamin D in the body. If this is combined with eating few dietary sources of vitamin D then risk of inadequate vitamin D is even greater.
Runners with lactose intolerance - this inability to digest milk sugar means that the main dietary source of vitamin D – that found in milk – is absent from the diet.
Runners with dark skin – the ability to produce vitamin D from sunlight exposure varies with the amount of skin pigmentation; the darker one’s skin, the lower the production of vitamin D.
What should you do?
Ask your family doctor to do a blood test for Vitamin D. The best time to do the test is when your diet is the main provider of Vitamin D - that would be between January-March. Vitamin Di levels tend to be the highest in the late summer as a result of UVB radiation from the sun helping us to make our own Vitamin D.
Runners (and anyone) over 50 yrs of age should take a supplement containing 400 IU of vitamin D. You may need even more - a blood test will help you and your doctor to determine how much supplementation you may or may not need. Include good food sources of vitamin D in your diet to help you get the vitamin D your body needs. Fortified foods (foods with vitamin D added to them) are common sources of vitamin D. In Canada, milk, margarine, and some yogurts are fortified with vitamin D. Fish and eggs are other good sources of vitamin D. Listed below are common sources of vitamin D.
Fortified soy beverage* 250 mL (1 cup) 120 IU
Margarine 5 mL (1 tsp.)60 IU
Milk 250 mL (1 cup) 100 IU
Mackerel 90 g ( 3 oz.)310 IU
Salmon, canned 90 g (3 oz.)650 IU
Sardines, 1 can 100 g (3.75 oz.)250 IU
Tuna 90 g (3 oz.) 236 IU