SAN FRANCISCO — A majority of 1,536 elderly women taking medication to prevent or treat osteoporosis were deficient in vitamin D, a study of community-dwelling patients found.
The findings echo a previous study that found 56% of medical inpatients had vitamin D deficiency. “This is a very common problem” that deserves more attention, Dolores M. Shoback, M.D., said at a meeting on osteoporosis sponsored by the University of California, San Francisco.
Physicians should look more carefully for vitamin D deficiency in inpatients and outpatients, even those who are ambulatory, on prescription therapy for osteoporosis, and lacking risk factors for vitamin D deficiency—“many of the patients, probably, in our own practices,” said Dr. Shoback, professor of medicine at the university.
The recent outpatient study included postmenopausal women at 61 locations in North America who had been taking bisphosphonates, calcitonin, or a selective estrogen receptor modulator for at least 3 months under a physician's care to prevent or treat osteoporosis. They averaged 71 years in age, and were 92% white.
Investigators administered a questionnaire to assess risk factors for vitamin D deficiency and measured the women's serum concentrations of parathyroid hormone (PTH) and 25-hydroxyvitamin D—known as 25(OH)D—the form of vitamin D stored in the body.
They found that 52% of the 1,536 women had levels of 25(OH)D lower than 30 ng/mL. Of these, 36% had levels below 25 ng/mL, and 18% were below 20 ng/mL, showing that most of the women with inadequate vitamin D were severely deficient (J. Clin. Endocrinol. Metab. 2005;90:3215–24).
“We aren't doing a good job with the people we're actively treating for osteoporosis,” said Dr. Shoback. Vitamin D deficiency is one of the most common causes of secondary osteoporosis.
Although there's no consensus on how much vitamin D the human body needs, the idea that 15–25 ng/mL is adequate has been replaced in the last few years by general cutoffs closer to 30 ng/mL or higher, she said. Some experts say people need at least 20 ng/mL 25(OH)D or else PTH levels rise and frank hyperparathyroidism develops. Others say that elderly people need 32–36 ng/mL to maximize intestinal calcium transport.
In the study, patients tended to develop secondary hyperparathyroidism at 25(OH)D levels of 25 ng/mL and lower. Many physicians use PTH levels to help diagnose vitamin D deficiency, but the study found that high PTH is not 100% sensitive for low vitamin D. Only 75% of women with 25(OH)D levels of 0–9 ng/mL had secondary hyperparathyroidism. “This surprised me,” Dr. Shoback said.
Women who had not discussed vitamin D and bone health with their doctors were more likely to have 25(OH)D levels below 30 ng/mL. “Sometimes we think we're talking to the wall or ourselves, but these discussions actually may be having some kind of an impact,” she said.
Other risk factors for vitamin D deficiency included age older than 80, a body mass index over 30 kg/m
The 1998 inpatient study that detected vitamin D deficiency in 56% of 290 patients consecutively admitted to a hospital medical service also found that risk factors predicted the deficiency only about 60% of the time. The investigators recommended that medical inpatients be screened for vitamin D deficiency, she noted. Taking multivitamins did not prevent vitamin D deficiency in that study.
Dr. Shoback said that she has no affiliation with companies that make vitamin D supplements.