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Vitamin D – Special Issue

Over the last few years I have reported on numerous studies linking vitamin D deficiency with various diseases: diabetes, heart attacks, at least 30 types of cancer, and autoimmune disease such as lupus and rheumatoid arthritis (a list of these reports appears below).

This winter I have had a series of baffling exercise- associated muscle injuries. My blood levels of vitamin D have been extremely low, even though I spend a lot of time outside riding my bike. I reviewed my diaries and found that wintertime injuries have been a lifelong pattern for me. I have not been able to find any strong evidence that lack of vitamin D causes muscle injuries. However, it is associated with muscle weakness, falling in older people, bone deformities and fractures.

People get most of their vitamin D from sunlight. The skin has an enormous capacity for vitamin D production and supplies the body with 80-100 percent of its vitamin D. However, a recent study showed that a high percentage of people in sunny Arizona are vitamin D deficient (American Journal of Clinical Nutrition, March 2008). How can this be? A clue to the problem is that a large percentage of the people who were deficient were African- American, Hispanic, elderly or overweight. We know that people who have dark skin need more vitamin D because dark skin blocks the sun's UVB rays that make vitamin D. Another study showed that almost 50 percent of African Americans in Boston had low vitamin D in March. We also know that obesity can cause vitamin D deficiency because body fat removes vitamin D from circulation. Furthermore, as people age, skin cannot synthesize vitamin D as efficiently and the kidneys are less able to convert vitamin D to its active hormone form.

An article from Australia showed that 15 out of 18 gymnasts in Australia suffered from vitamin D deficiency (Clinical Journal of Sport Medicine, March 2008). These athletes spend a lot of time training indoors. Even if you spend several hours a day outside in winter, you probably will not get enough sun to meet your vitamin D needs. At our latitude the sun's rays reach earth at an angle so they have to penetrate a thick layer of the earth's atmosphere and fewer rays get through. Also, when the weather is cold we cover most of our skin with clothing.

My personal plan and recommendations

While we wait for the scientific community to resolve whether lack of vitamin D causes cancers, heart attacks and so forth, or is just a marker for other risk factors such as lack of activity or excess weight, I think you should be aware of your own vitamin D status and take action if you are deficient.

If you seldom go outdoors, have dark skin, are over 50 or are overweight, I recommend that you ask your doctor to do blood tests for vitamin D3 and D2. D3 is made by your skin from ultraviolet light (UVB) or from the vitamin D you get in foods or supplements. D2 comes just from food or supplements. Your total blood level of vitamin D should be over 50. If it is below 50, you may need to take a tropical vacation, use a tanning bed or take vitamin D supplements. A safe dose appears to be 1000 IU per day during the winter.

Until summer arrives and my vitamin D levels return to normal, I have chosen to use a tanning salon. I am reluctant to take supplements because one study from Australia suggests that they may suppress the body's ability to synthesize vitamin D.

Tanning lamps emit both UVA and UVB. However, because UVB are the primary rays that cause skin cancer, most tanning beds are high in UVA which does not make vitamin D and low in UVB that makes vitamin D. Ask the tanning center about the amount of UVB in their lamps. Some have 70 percent UVA and 30 percent UVB, but some emit less than five percent UVB. If you use a tanning bed, start at very low exposure, preferably with less than five minutes on your first visit. You won't know if you have burnt yourself until that evening. Then add only two minutes per exposure and don't go every day. After a couple of weeks, you can repeat your blood test. Stop using tanning bed when your total level reaches 50. If it does not reach 50 in a month, you should stop the tanning bed and take vitamin D supplements.

I will report to you from time to time on the progress of my training program, injuries and vitamin D levels; and I will continue to survey the scientific literature for studies on the association between vitamin D and various health problems.


My previous reports on vitamin D:

Heart attacks and vitamin D

Cancer and vitamin D

Diabetes and vitamin D

Other vitamin D studies

More information on vitamin D:


Recipe of the Week

Baked Salmon with Portobello Mushrooms

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June 25th, 2013
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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