Back grey_arrow_rt.gif
 
 
Vitamin D Levels Predict Bisphosphonate Response
 
 
  By Nancy Walsh, Staff Writer, MedPage Today

Published: September 20, 2011

SAN DIEGO -- Postmenopausal women with low levels of circulating vitamin D are much less likely to respond to treatment with bisphosphonates, researchers said here.

Action Points

· Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

· Explain that postmenopausal women with low levels of circulating vitamin D are much less likely to respond to treatment with bisphosphonates.

· Point out that for each 1 ng/mL decrease in 25(OH)D level, there was a 5% decrease in likelihood of responding to treatment with bisphosphonates.

Women whose mean level of serum 25 hydroxy vitamin D (25[OH]D) was at least 33 ng/mL were almost five times more likely to benefit from bisphosphonates than those whose levels fell below that cutoff (OR 4.53, 95% CI 2.17 to 9.48, P<0.0001), according to Amanda Carmel, MD, of Weill Cornell Medical College in New York City, and colleagues.

In addition, for each 1 ng/mL decrease in 25(OH)D level, there was a 5% decrease in likelihood of responding to treatment (OR 0.95, 95% CI 0.92 to 0.98, P=0.0007), Carmel reported at the annual meeting of the American Society for Bone and Mineral Research.

Clinical trials have shown clear and durable benefits in bone mineral density (BMD) and decrease in fracture risk with bisphosphonate use, but equivalent results are not always seen in clinical practice.

"We hypothesized that good response to bisphosphonates in a real-world setting would be associated with higher mean vitamin D levels, and to test this hypothesis we conducted a chart review in two New York City ambulatory practices," Carmel said.

The study included 210 women who had been on bisphosphonates for at least 18 months. Almost all were white (83%) with a mean age of 66. The mean femoral neck T score was -2.

They were considered nonresponders if their T score remained below -3 with treatment, if they had a decrease in BMD of more than 3%, or if they had an incident fracture while on therapy.

They were classified as responders if their T scores were maintained above -3, their BMD was stable, and they had no fractures.

About half were being treated with alendronate (Fosamax), one quarter with risedronate (Actonel), and the remainder with ibandronate (Boniva) or zoledronate/zoledronic acid (Zometa).

Slightly more than half were nonresponders (111 versus 99), with the most common reason for nonresponse being a loss of 3% or more in BMD while on treatment.

Factors that were associated with nonresponse included older age, longer bisphosphonate use, and low vitamin D levels.

The researchers then looked at response according to specific 25(OH)D levels, with 33 ng/mL being a level thought to be associated with decreased fracture risk.

After adjusting for age, body mass index, type of bisphosphonate, and duration of treatment, they confirmed that a level of at least 33 ng/mL had the highest odds ratio for response to bisphosphonates, as well as the strongest P-value (4.5-fold greater odds of bisphosphonate response, estimated OR 4.5, P=0.0001).

"This level [33 ng/mL] is higher than that recommended by the Institute of Medicine as adequate for the general population, and many patients have levels well below this, so vitamin D supplementation may need to be higher for this therapeutic outcome," Carmel said.

Primary source: American Society for Bone and Mineral Research

Source reference:

Carmel A, et al "The 25(OH)D level associated with a favorable bisphosphonate response is >33 ng/mL" ASBMR 2011; Abstract 1137.

 
 
 
  icon paper stack View Older Articles   Back to Top   www.natap.org