Vitamin D More Important Than Calcium for Bone Health
To maintain normal calcium metabolism, a person’s vitamin D status appears to be more important than supplementing with calcium, reports a study in the Journal of the American Medical Association (2005;294:2336–41). The results of this study suggest that assuring adequate vitamin D levels might provide greater protection against osteoporosis than taking calcium every day.
Calcium supplements are heavily promoted and widely used for osteoporosis prevention and treatment. Although vitamin D is needed for calcium to be absorbed, many popular calcium products do not contain it. Research has repeatedly shown that vitamin D deficiency is common, with a prevalence as high as 40% or more in some studies. The main cause of low vitamin D status is lack of sun exposure. Many people spend the bulk of their time indoors and those who do go outside often cover themselves with clothing or wear sunscreen because of fears that sun exposure will age their skin or cause skin cancer. While excessive sun exposure can be dangerous, a modest amount of sunlight appears to be safe and is all that is needed by most people to get enough vitamin D.
In the new study, dietary calcium intakes and blood levels of 25-hydroxyvitamin D (the standard laboratory test for vitamin D status) were measured in 944 healthy adults living in Iceland. The efficiency with which their bodies utilized and metabolized calcium was estimated by measuring blood levels of parathyroid hormone, with lower levels indicating more efficient handling of calcium.
People were divided into groups according to calcium intake (less than 800 mg per day, 800 to 1,200 mg per day, and greater than 1,200 mg per day) and serum 25-hydroxyvitamin D levels (below normal, marginal, and normal). Better vitamin D status was found to be associated with more efficient calcium metabolism, whereas the association between calcium intake and efficiency of calcium metabolism was not statistically significant. The researchers concluded that, as long as vitamin D status is sufficient, taking more than 800 mg of calcium per day might not be necessary for maintaining healthy bones. On the other hand, high calcium intakes will not ensure optimal bone health if vitamin D levels are low. Of course, even if vitamin D status is good, a low calcium intake (less than 800 mg per day) may increase the risk of bone loss.
In addition to calcium and vitamin D, a number of other nutrients have been shown to play a role in bone health. These include magnesium, manganese, zinc, copper, boron, strontium, silicon, vitamin K, folic acid, vitamin B12, phosphorus, and vitamin C. Maintaining strong bones presumably requires adequate intake of all of these nutrients.
An expert in nutritional therapies, Chief Medical Editor Alan R. Gaby is a former professor at Bastyr University of Natural Health Sciences, where he served as the Endowed Professor of Nutrition. He is past-president of the American Holistic Medical Association and gave expert testimony to the White House Commission on Complementary and Alternative Medicine on the cost-effectiveness of nutritional supplements. Dr. Gaby has conducted nutritional seminars for physicians and has collected over 30,000 scientific papers related to the field of nutritional and natural medicine. In addition to editing and contributing to The Natural Pharmacy (Three Rivers Press, 1999), and the A–Z Guide to Drug-Herb-Vitamin Interactions (Three Rivers Press, 1999), Dr. Gaby has authored Preventing and Reversing Osteoporosis (Prima Lifestyles, 1995) and B6: The Natural Healer (Keats, 1987) and coauthored The Patient's Book of Natural Healing (Prima, 1999).
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