Women in the study who took hormone replacement therapy that included progestin along with estrogen performed worse on hearing tests than women who did not take hormone therapy and those who took estrogen alone.
Researcher Robert D. Frisina, PhD, tells WebMD the hearing loss attributable to progestin use was in the range of 10% to 30%.
It is not clear, however, if length of time on progestin therapy impacts risk, Frisina says, or if the hearing loss reverses when treatment is stopped.
The study was published Tuesday in the Proceedings of the National Academy of Sciences.
"Our findings suggest that this is one more possible side effect that women should consider when they make their decision about whether or not to take hormone therapy with progestin," Frisina says. "That is particularly true for women who already have some hearing loss."
However Wendy Klein, MD, FACP, senior deputy director of the Institute for Women's Health at Virginia Commonwealth University, says the study was too small and had too many other limitations to provide useful information to women considering such therapy.
Smallest Doses, Shortest Time
Hormone therapy -- estrogen plus progestin for women who have not had hysterectomies, and estrogen alone for those who have -- is widely regarded as the most effective treatment for hot flashes and other symptoms related to menopause.
For women with an intact uterus, the addition of progestin in hormone replacement therapy reduces the risk of uterine cancer from estrogen.
But hormone therapy use plummeted virtually overnight in the summer of 2002 with the publication of a large, government-run study linking hormone therapy with an increased risk of heart attacks, strokes, blood clots, and breast cancer.
Experts now recommend that women take the smallest doses of hormone therapy they can for the shortest time necessary to effectively treat menopausal symptoms.
Frisina speculates that progestin may damage hearing by impairing hearing-related nerve cell receptors within the ear and brain.
He recommends that women who are considering taking progestin have a hearing test before starting treatment. They should then be tested on a regular basis every six months or so, while they are on the hormone, he says.
Frisina, who is associate director of the International Center for Hearing and Speech Research at the Rochester Institute of Technology, says his research team will continue to study the impact of progestin on hearing.
Among the most important unanswered questions, he says, is whether hearing loss reverses with discontinuation of treatment and the impact of cumulative dosage.
"I would guess that the less time a women is on this therapy the better," he says.
Room for Doubt
Thirty-two women who took combined hormone therapy with estrogen and progestin were included in the study, along with 30 women who took estrogen alone, and 62 women who did not take any hormone therapy.
The researchers worked to exclude women who had taken other medications associated with hearing impairment. But they relied on the women, who were no younger than 60 and as old as 86, to remember if they had taken such drugs.
"It isn't likely that an 86-year-old woman, or a woman of any age, will be able to look back and remember every medication she has taken," Klein tells WebMD. "So it is almost impossible to know if the findings were influenced by the use of other medications."
Klein, who is also deputy editor for the journal Women's Health, adds that the wide range of hormone usage times among women in the study makes it "almost impossible" to accurately determine if the hearing loss was treatment related.
The hormone therapy users in the study took the treatment for as little as five years and as long as 35 years.
Finally, Klein questions the researchers' failure to include information on route of hormone administration and the hormone doses given to women in the study.
"Years ago, we typically used higher doses of hormone therapy," she says. "Now we know that we can use a fraction of the dose that we once used."