ESTROGEN THERAPY MAY HOLD BENEFIT FOR MORE WOMEN : OSTEOARTHRITIS RISK CUT, STUDY SAYS.

Byline: Susan Gilbert The New York Times

In addition to protecting against heart disease and osteoporosis, estrogen replacement therapy may have another benefit for postmenopausal women: A large new study suggests that it lowers the risk of osteoarthritis.

The finding is important because there is currently no way to prevent the disease, which is the most common form of arthritis. It affects 16 million Americans, mostly women over the age of 45.

Osteoarthritis of the knee and hip accounts for at least 70 percent of the more than 200,000 hip and knee replacement operations performed in the United States each year, according to the new research, which will appear in the Oct. 14 issue of Archives of Internal Medicine.

The study involved 4,366 white women 65 and older who were being followed for incidence of hip fractures. African-American women were excluded from the study because they have a low incidence of such fractures.

For this report, researchers looked at another problem: osteoarthritis of the hip. The women who were taking estrogen replacement therapy had the lowest incidence of this ailment. Incidence was measured by X-rays that revealed physical characteristics of the disease, like narrowing of the spaces between the bones and the growth of bony spurs.

The lower risk was found only in women who were currently using supplemental estrogen and in those who had stopped using it less than 10 years before they were examined. Those who had stopped using estrogen 10 or more years earlier had the same risk for the disease as women who had never taken estrogen, the study found.

The risk for women who had been taking estrogen for 10 or more years was 8.4 percent, as against 13 percent for women who had never taken estrogen. The risk for women who had been taking estrogen for one to 10 years was about 10 percent.

The researchers found nearly as strong an association for women taking postmenopausal hormone therapy that contained estrogen and progestin. But the number of women taking the combination therapy was too small for the study to draw any conclusions about its effect on osteoarthritis.

Arthritis experts had long speculated that estrogen played a role in osteoarthritis, since the disease is most prevalent among women who have gone through menopause, a period when natural estrogen levels plummet.

``There's good reason to believe that estrogen is involved because there is a rapid increase in the incidence of osteoarthritis in women after menopause,'' said Dr. Michael C. Nevitt, the lead researcher of the study, who is an epidemiologist at the University of California, San Francisco.

It is not known how estrogen might protect against osteoarthritis, Nevitt said, but a leading theory is that it somehow helps prevent the abnormal changes in bone structure, like the thickening of the bone and the formation of cysts, that are associated with the disease. He said these abnormalities might cause biomechanical changes that in turn weaken the cartilage around the bones.

The new study confirms the findings of two small studies that had shown a lower incidence of osteoarthritis of the knee and hip in women who took estrogen replacement therapy.

Dr. Steven R. Cummings, chief of internal medicine at UC San Francisco, who was involved with the latest study, said that estrogen would probably also protect against arthritis in other joints.

The researchers cautioned that more studies would be needed before doctors could recommend estrogen replacement therapy to prevent osteoarthritis. They are now following the women in the current study to see if estrogen replacement therapy will actually prevent the onset of osteoarthritis in the future.

Doctors who treat arthritis said the evidence from the current study was promising.

``It looks good,'' said Dr. Doyt Conn, senior vice president for medical affairs at the Arthritis Foundation in Atlanta. ``It raises the potential importance for estrogen replacement therapy for lowering the risk of osteoarthritis.''