When postmenopausal women discontinue hormone therapy, their bone mineral density drops and their risk of a hip fracture climbs, new research suggests.

Among nearly 81,000 postmenopausal women followed for six and a half years, stopping hormone therapy was linked with an overall 55 percent increased risk of hip fracture.

The jump in chances of a fracture was apparent as soon as 24 months after women stopped hormone therapy and was not affected by the use of bone-building bisphosphonate drugs, report Dr. Roksana Karim, from the University of Southern California, Los Angeles, and her colleagues in the journal Menopause.

Millions of postmenopausal women stopped taking hormone therapy after findings from the Women’s Health Initiative (WHI) in 2002 suggested it raised the risk of heart disease and some cancers.

Previous research has shown conclusively that menopausal women on hormone therapy have substantially less bone loss relative to women not taking the hormones, Karim told Reuters Health.

“It has also been known for a while that women who do not take hormones after the menopause have a much greater risk of suffering a bone fracture than women who do take hormones,” she added.

“This new study,” Karim said, “shows quite nicely that when hormone therapy is stopped, the risk for hip fracture goes up substantially. Women halting hormone therapy should definitely be advised by their clinicians about the increased risk of fracture.”

The study looked at 80,955 postmenopausal women from the Southern California Kaiser Permanente Health Maintenance Organization who were at least 60 years old and had filled prescriptions for hormone therapy at least once between January and June 2002. The women were followed through December 2008. Most were white (54 percent), and, on average, slightly overweight.

As expected — because of the WHI results announced in 2002 — use of hormone therapy dropped off significantly between July 2002 and December 2008 (from 85 percent to 18 percent of women in the study). During this same period, the annual hip fracture rate increased from 3.9 to 5.67 per 1,000 women.

Based on those rates, women who discontinued hormone therapy were one and a half times as likely to have a hip fracture as the ones who continued taking the hormones.

The risk increased as early as two years after hormones were stopped and it kept rising incrementally, from 52 percent increased risk at two years to 77 percent higher risk at five years or longer after ceasing to take the hormones.

A longer time off the medication was also linked to lower bone mineral density.

“Our data confirm the rapidity of bone loss and increased hip fracture incidence with hormone therapy cessation,” the authors note in their report.

“Our results should encourage women and clinicians to take a second look at the bone health benefits of hormone therapy,” Karim said. “It may be time to rethink the guidelines about hormone therapy for women with an increased risk of hip fracture.”

She added, women “should consult their physicians to determine if they are at high risk of bone loss, which may involve bone density scanning and a review of family history of fracture, and may want to consider individualized hormone therapy.”