Circulating vitamin D above a lower cut-off of 33 ng/ml was linked to seven times better results.
To fully optimize results of a drug therapy for osteoporosis and low bone mineral density (BMD), patients should maintain vitamin D levels above the limits recently recommended by the Institute of Medicine (IOM), according to a new study by researchers at the Hospital for Special Surgery in New York.
The study, presented June 6 at the Endocrine Society’s Annual Meeting in Boston, demonstrated that maintaining a circulating vitamin D level above 33 ng/ml is associated with a seven-fold greater likelihood of having a more favorable outcome with bisphosphonate therapy.
Last November, the IOM issued recommendations that 25-Hydroxy vitamin D levels of 20-30 ng/ml in the blood were adequate for normal, healthy people. But “you are seven times more likely to respond to bisphosphonates if your 25-Hydroxy vitamin D level is 33 ng/ml and above," says study leader Richard Bockman, MD, PhD, a specialist in bone metabolism. "So if you want to see a particular outcome from this treatment, then maybe 20 to 30 is not appropriate. When you see a seven times greater effect, that is pretty impressive.”
20 Million Take the Drugs; Many Aren’t Helped
More than 20 million people take bisphosphonates to preserve and improve skeletal health, and reduce the risk of fractures that can be caused by low BMD and osteoporosis. Normally, new bone formation is balanced by a natural process that dissolves older cells. Biphosphonate drugs are prescribed to slow or stop the reabsorption phase of the cycle. But the drugs do not work well in some patients.
Because vitamin D is important to bone health, the researchers investigated whether they could identify levels of vitamin D that are associated with improved outcomes in patients taking bisphosphonates. They conducted a retrospective chart review of 160 patients seen in an osteoporosis practice of the Hospital for Special Surgery.
• They identified subjects who were female, postmenopausal, had been taking one of four FDA-approved bisphosphonate drugs for at least 18 months, and had undergone at least two BMD scans separated by 18 to 60 months. (The four drugs are alendronate, residronate, ibandronate and zolendronate.)
• Patients were not included if they were nonadherent to bisphosphonate therapy, were chronic steroid users, or had metabolic bone disease or chronic kidney disease.
• The researchers collected data on age, body mass index, type of bisphosphonate taken, treatment duration, concurrent calcium supplementation, fracture prior to and during bisphosphonate therapy, BMD and “T score” at four sites - lumbar spine, femoral neck, trochanter, and total hip - from the two most recent bone scans.
“The way the data are expressed for a bone density is how many standard deviations you are away from the normal,” Dr. Bockman explains. “One standard deviation from the normal is a T score of one. Two standard deviations is a T score of two. Below the normal, it is a minus two and above the normal is a plus two. If your bone density is more than 2.5 standard deviations below the normal, that defines a low bone mass that is considered to be osteoporosis.”
The researchers also collected data on circulating levels of vitamin D, obtained with and between the two most recent bone scans.
Patients were deemed nonresponders if they had more than a 3% decrease in BMD between the initial and follow-up bone scans, a low-trauma fracture or a T-score less than minus 3.0 despite at least 24 months of bisphosphonate therapy.
• Of the 160 patients in the study, 89 were responders, and 71 were nonresponders, with 42 having decreased BMD, 17 sustaining a fracture, and 12 having a persistent low T-score.
• The investigators found that only 16.8% of responders but 54.9% of nonresponders had vitamin D levels less than 33 ng/ml.
• Patients with an average circulating vitamin D level of 33 ng/ml and above had a seven-fold greater likelihood of having a favorable response to bisphosphonates.
“We selected 33 as the cutoff and subsequently showed that it was the right choice, with more being better,” says Dr. Bockman.
Nonresponse rates were higher in patients who had low levels of vitamin D: less than 20 ng/ml (83.3%), 20-30 ng/ml (77.8%), 30-40 ng/ml (42.3%), and more than 40 ng/ml (24.6%).
“If you look at the medical literature, researchers talk perhaps about a 20% increase in response rate, occasionally a doubling, but when you see a sevenfold improvement in outcome, you have to be impressed that it is probably important,” Dr. Bockman says.
Before this study, researchers had not formally studied the relationship between vitamin D levels and the effectiveness of bisphosphonates, and “there has been a lot of controversy over the correct vitamin D level for people to have,” Dr. Bockman observes. But the new research shows “Vitamin D status should be optimized to improve outcomes in patients taking bisphosphonates.”
Further, he notes, three associations with an interest in bone health - the American Geriatric Society, the Endocrine Society, and the American College of Rheumatology - are coming out with or have guidelines that recommend vitamin D levels higher than the IOM recommended levels for healthy people.
Source: Source: Hospital for Special Surgery, news release Jun 6, 2011
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