When I talk with patients about osteoporosis prevention and treatment, I use the analogy of building a house: Calcium and vitamin D are the foundation of the house, and you can't build a house without a foundation.
It is unfortunate that more women are not receiving this message, particularly the lesser-appreciated part of the message that some women need supplementation with 1,000 international units of vitamin D3 (cholecalciferol)—more than is typically included in supplemental calcium-vitamin D combinations—to have that strong foundation.
The recently reported Women's Health Initiative study sends an important message. Those healthy postmenopausal women who best adhered to regimens of daily supplementation with calcium and modest amounts of vitamin D3 (400 IU) had a reduction in fracture risk, while those who were less adherent did not do as well.
But we also must better appreciate the fact that vitamin D inadequacy is common among women receiving osteoporosis therapy—even among women receiving such modest supplementation—and that inadequate vitamin D status is associated with secondary hyperparathyroidism, increased bone turnover, bone loss, diminished muscle strength and function, and increased risk of falls.
If we're going to intervene pharmacologically and spend 0 a year or more on osteoporosis drugs, I think that the approximately – we would spend on testing vitamin D status is money well spent—especially since vitamin D supplementation itself is extremely low cost. There are a number of places where patients can purchase 1,000-IU capsules of vitamin D3 at a cost of a month. (I ask patients to purchase vitamin D3 rather than vitamin D2 because there is some evidence that patients maintain higher vitamin D blood levels when vitamin D3 is utilized.)
We can feel more confident pursuing such a public health approach today than ever before for several reasons: For one, experts have basically agreed that approximately 30 ng/mL of serum 25-hydroxyvitamin D (25OHD) is a good cutoff value for diagnosing vitamin D inadequacy. Some researchers might still argue whether it should be 26 or 32 ng/mL, but there is now solid, reasonable consensus among international experts on a 30-ng/mL cutoff.
Second, the assays for 25OHD have improved. Until recently, we did not have reliable clinical tools for detecting hypovitaminosis D in our patients. Serum 25OHD measurements varied widely between laboratories.
Today, however, there are at least three good assays that physicians can feel reasonably confident with: DiaSorin RIA [radioimmunoassay], high-performance liquid chromatography, and tandem mass spectrometry. These assays are widely available. From my experience, I know that the Mayo Clinic's laboratory is among the large labs offering tandem mass spectrometry commercially, and many smaller laboratories are offering the other two tests. Additionally, these tests are commonly covered by patients' insurance plans.
Along with these developments, of course, there is the increasing recognition among experts over the past 5–10 years that vitamin D inadequacy is both harmful and common, even in those women taking multivitamins or combined calcium-vitamin D supplements.
In a study published last year, we looked at 1,500-plus community-dwelling, postmenopausal North American women receiving therapy to treat or prevent osteoporosis. We found that more than half of these women had vitamin D inadequacy. Serum 25OHD was less than 20 ng/mL in 18%, less than 25 ng/mL in 36%, and less than 30 ng/mL in 52%. Such a prevalence isn't surprising. With concerns about skin cancer and premature aging, our patients don't want sun exposure.
We should no longer be surprised longer by studies documenting the harmful effects of vitamin D inadequacy and the benefits of vitamin D supplementation.
Among recent studies are a metaanalysis published 2 years ago in the Journal of the American Medical Association showing that vitamin D supplementation reduced the risk of falling among older individuals with stable health by more than 20%, and a randomized, double-blind study published in 2003 in the British Medical Journal in which men and women were mailed one capsule containing 100,000 IU of vitamin D3 or a placebo every 4 months for 5 years. The total fracture incidence was reduced by 22% in the vitamin D group.
The Institute of Medicine's Food and Nutrition Board has not reviewed the issue of vitamin D in many years. The recommended daily intake currently stands at 400–600 IU, while experts agree that we need around 1,000 IU. Among other benefits, a change in the recommended intake for vitamin D could provide added impetus to the food industry to increase the number of foods fortified with vitamin D. Although it would not alleviate the problem—and should not diminish our vigilance as physicians—such change would help.
DR. BINKLEY is an associate professor at the University of Wisconsin-Madison's Osteoporosis Clinical Center and Research Program, associate director of the UW Institute of Aging, and president of the International Society for Clinical Densitometry.