Vitamin D is crucial for calcium absorption. Dietary sources are mainly fortified foods such as milk, other dairy products, and some orange juices as well as oily fish and cod liver oil. Vitamin D is also manufactured by the body when skin is exposed to sunlight. People who get little or no sun exposure tend to have higher rates of breast, colon and prostate cancer plus MS. Sunscreens reduce the body’s absorption of vitamin D. Many scientists believe if you get 10-15 minutes of sun exposure on your face and arms at least twice a week, you may not need to consume any dietary vitamin D or supplements.
The Women’s Health Initiative contained a study of the effect of higher dosages of calcium and vitamin D on bone density, fractures and colorectal cancer. Some of the data is conflicting. For example, the WHI showed no clear benefit from calcium supplements even when combined with vitamin D (1000 mcg of calcium and 400 IU of vitamin D daily). In those women taking the supplements, bone density slightly improved, risk of fracture did not improve, and risk of colon cancer was no lower.
More recently, a study led by the University of Pittsburgh Graduate School of Public Health determined that women with low levels of vitamin D have an increased risk of hip fracture. The authors of this study, a professor of epidemiology and her colleagues, reviewed patient data from 400 women who had been enrolled in the WHI for seven years and had experienced hip fractures. Comparing their levels of 25 hydroxyvitamin D, an indicator of vitamin D status, to a control group, the authors noted that as vitamin D concentrations decreased, risk of hip fractures climbed.
Says the lead scientist, Dr. Jane Cauley: “The risk of hip fractures was 77 percent higher among women whose 125 hydroxyvitamin D levels were at the lowest concentrations. This effect persisted even when we adjusted for other risk factors such as body mass index, family history or hip fractures, smoking, alcohol use, and calcium and vitamin D intake.”
Find the full article at www.upmc.com.
How can one study conclude low levels of vitamin D increase the risk of hip fractures and another conclude that increased vitamin D does not lower the risk of hip fractures?
There are some problems with the WHI study. Namely:
- The placebo group took calcium and vitamin D on their own
- Most patients got adequate calcium and vitamin D from food
- There were relatively few fractures in the group as a whole
- It may take more than 400 IU of vitamin D to reduce fracture risk or influence cancer
- Not all participants took the prescribed amount of supplements for the duration of the study (seven years)
Perhaps the recent study is more reliable since the authors targeted a smaller, well-defined group of patients.
If you believe that higher amounts of vitamin D will protect your bones, you may not be able to get enough from food or sunlight. This is partly because the ability to manufacture vitamin D from sunlight and utilize it declines with age. It’s nearly impossible to get enough without supplementation.
Current recommended intake is 200 IU for people aged 50 and under, 400 IU for those 51-70, and 600 IU for those over 71. Growing numbers of scientists and health authorities believe that more is better—up to a point (since vitamin D is a fat soluble vitamin and thus can be stored in the body). Those aged 70 and over should take 800-1000 IU daily, especially those people with dark skin or African Americans.
There are two main forms of vitamin D: vitamin D3 or cholecalciferol and vitamin D2 or ergocalciferol. Once consumed, both are converted in the body to the active form. D2 has been found to be less than one-third as potent as D3 and shorter-acting.
Many supplements (including One-A-Day and Centrum) contain D3. Quite a few health food store brands contain D2 (Solgar, Nature’s Plus, Rainbow Light, KAL). At least one Vitamin Shoppe supplement (Mega-Vites) contains D2. Look for D3 or cholecalciferol on your supplement bottles.
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