Vitamin D Deficiency May Be Genetic

A report from University of Toronto shows that genetic factors cause some people to develop severe vitamin D deficiency while others do not (Clinical Biochemistry, July 2009). An earlier study showed that some people and mice have abnormal Vitamin D binding protein (VDBP) and therefore cannot respond to vitamin D normally (Endocrine Reviews, June 2008). They are at increased risk for heart attacks, strokes, certain cancers, depression, athletic injuries, muscle weakness and so forth.

Over the years I have been unable to run effectively in the winter and injuries forced me to miss six Boston Marathons. This same pattern of winter-time weakness and injuries plagued me when I switched to cycling. It wasn't until a few years ago that I drew blood and found that my vitamin D3 (Cholecalciferol) was 22 nmol/L (normal is greater than 75). Taking as much as 3000 IU of vitamin D failed to get my blood levels much over 30. I moved to Florida and rode my bike very well last winter. This winter was extremely cold and often cloudy, and my injury and weakness pattern recurred from January through March. I notice that a good day in the sun allows me to ride well for about three or four days, but the weakness and injuries recur until the next day of warm sunlight. My skin has never been damaged by sunlight, has no pre-cancers and looks much younger than my 74 years.

Vitamin D deficiency is associated directly with muscle weakness (Scandanavian Journal of Medicine & Science in Sports, October 2009) and athletic injuries (Current Opinion in Clinical Nutrition & Metabolic Care, November 2009; Molecular Aspects of Medicine, December 2008). It is my opinion that:

• Certain people are genetically susceptible to vitamin D deficiency
• These people are likely to be injured when they try to exercise vigorously in the winter
• Vitamin D pills will help some athletes, but many do not regain their athleticism at conventional doses
• These people may get better when they are exposed to sunlight during exercise. Of course they should be concerned about skin cancer from excess sunlight, but I think that people who are at high risk for vitamin D deficiency are at reduced risk for skin cancer. However, I have no available data to support that impression.
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