Despite some hopeful hints from earlier research, a new study finds that older women on hormone replacement therapy may not gain any protection from disability as they age.

Researchers have speculated that waning estrogen levels may contribute to muscle loss and other declines in physical function as women age. Muscle cells have receptors for estrogen, and recent research has linked higher blood levels of the hormone to greater muscle strength in elderly women.

The findings raise the question of whether women on hormone replacement therapy (HRT) tend to have better physical functioning as they age compared with women who never took hormones.

The current study, reported in the journal Menopause, suggests this is not the case.

Researchers found that among nearly 2,400 older women who had been randomly assigned to take HRT or a placebo, both groups showed similar dips in muscle strength and walking speed over six years.

The women in the study were all age 65 or older when they started taking HRT, so it is not clear whether hormone replacement at younger ages might help preserve a woman’s physical functioning, note the researchers, led by Dr. Yvonne L. Michael of Drexel University School of Public Health in Philadelphia.

But for now, they conclude, the findings suggest that HRT does not stave off physical decline and disability in older women.

The findings are based on a subgroup of women who had taken part in the Women’s Health Initiative (WHI), a large U.S. clinical trial begun in 1993 in which postmenopausal women were randomly assigned to take either HRT or placebo pills.

The WHI was halted in 2002, when researchers found that women on HRT had higher risks of heart attack, stroke, breast cancer and blood clots than placebo users. As a result, experts now advise that while HRT is effective at relieving menopausal symptoms - like hot flashes and vaginal dryness - women should take it at the lowest dose and for the shortest time possible.

In their study, Michael and her colleagues focused on a subgroup of WHI participants who were age 65 or older and disability-free when they entered the study. Over six years, the women periodically took tests of physical function - including measures of grip strength, walking speed and their ability to sit down and get up from a chair.

On average, the researchers found, the women’s grip strength declined over time by 12 percent, while their walking pace slowed by 11 percent and their performance on the timed “chair-stand” test dipped by 3.5 percent. There were no significant differences between the HRT and placebo groups.

There was evidence that minority women improved their grip strength on HRT. However, Michael’s team writes, that finding should be “interpreted cautiously,” in part because there is no known reason for such an effect.

They say that future studies should look at whether there are, in fact, racial differences in any effects of HRT on women’s physical functioning.

SOURCE: Menopause, February 2010.