The largest study ever to analyze the hearing of women on hormone-replacement therapy has found that women who take the most common form of HRT have a hearing loss of 10 to 30 percent more compared to similar women who have not had the therapy. The results are being published on-line this week by the Proceedings of the National Academy of Sciences.
It's as if the usual age-related hearing loss in women whose HRT included progestin, a synthetic form of the hormone progesterone, was accelerated compared to women taking estrogen alone or women not taking HRT. On average, women who received progestin had the hearing of women five to 10 years older.
The results of the study involving 124 women confirm results from a smaller study that the same group reported in 2004 at the annual meeting of the Association for Research in Otolaryngology. The new results also identify progestin as the component of HRT doing possible damage.
"Whether a woman goes on HRT is certainly her decision, and she should discuss the options with her doctor," says senior author Robert D. Frisina, Ph.D. "In light of these findings, we feel that hearing loss should be added to the list of negative things to keep in mind when talking about HRT. Women especially who already have a hearing problem should weigh this decision carefully. Women on HRT should consider having a thorough hearing check-up done every six months."
Frisina is part of one of the world's leading groups in hearing research, the International Center for Hearing and Speech Research (ICHSR), which includes scientists from the University of Rochester Medical Center and the National Technical Institute for the Deaf at Rochester Institute of Technology. The center, funded by the National Institutes of Health, is a collaboration of two leading groups of scientists just down the road from each other: scientists at RIT/NTID who have extensive experience with research with people, and their counterparts at a top neuroscience program, including the Department of Otolaryngology, at the university.
In the study published in PNAS, a team of scientists, nurses and audiologists compared the hearing of healthy women ages 60 to 86 who were divided into three groups. Thirty women had taken a form of HRT that included only estrogen; 32 women had taken both estrogen and progestin; and 62 women had never been on HRT. Each group contained women whose health histories and other characteristics closely matched those of the women in the other groups.
Each of the women was tested with a battery of hearing tests. A standard "pure tone" test - a common hearing test where a person raises her hand or presses a button when she hears a tone - was used to measure which frequencies each woman could hear. In addition, the team did two sophisticated tests in which a sound was sent into each woman's ear, and then the echo coming back out was measured. These tests tell scientists how healthy a person's inner ear is, particularly the hair cells that convert noise to electrical signals that the brain interprets as sound. Finally, each woman underwent a "hearing in noise" test that measures how well the brain sorts out the multitude of signals traveling from the ear to the brain. Most of the painstaking tests are available only at a few major medical centers and other institutions that focus on hearing research.
By all measures, women whose HRT included progestin - the most common type of HRT -had worse hearing than the other groups. The tests showed that women who had received progestin had problems both in the inner ear and in the portions of the brain used for hearing.
The results also show no benefit to hearing for women who take a form of HRT that includes estrogen alone, a surprise to researchers who thought that estrogen might help hearing.
"It's long been thought that estrogen is good for nerve cells, so we wanted to see if women on estrogen as part of HRT had better hearing than women not on HRT," said Frisina, a neuroscientist at the University of Rochester Medical Center and Distinguished Researcher in Biological Sciences at Rochester Institute of Technology. "We were very surprised to find not only that women on estrogen did not hear better than other women, but that the women who were also on progestin actually heard worse."
The team asked the question about hormones as part of a wider research project into age-related hearing loss, or presbycusis, which is one of the chief complaints of older people. In past research the team has found that the problem stems not only from degradation of the inner ear but also from an aging brain that loses its ability to process and filter information as the years go by. As in most people with age-related hearing loss, the team, whose work is supported by the National Institute on Aging and the National Institute on Deafness and Other Communication Disorders, found that women on progestin had problems with both systems.
The group is continuing its studies, trying to figure out the exact effects of progestin on the ears and brain. Those effects are likely felt to some degree by all women, since progesterone is a natural hormone that enables a woman to carry a pregnancy. Other scientists have found that a woman's hearing can worsen slightly when her progesterone levels are high, during the latter portion of the monthly cycle.
The team also plans to study women who have gone off HRT, to see if the hearing loss might be reversible. And they say that women on the birth control pill, which includes progesterone, should also be studied.
The first author of the PNAS paper is Patricia Guimaraes, M.D., of the University's Department of Otolaryngology, who did much of the testing. Also part of the study were research nurse Susan Frisina of the University, who worked with the research subjects at the National Technical Institute for the Deaf; research audiologist Frances Mapes of NTID, who tested many of the subjects; Frisina's father, D. Robert Frisina, Ph.D., founding director of NTID, who directs the hearing research center; and otolaryngologist Sherif Tadros, M.D., of the University of Rochester.
Frisina, professor of Otolaryngology at the University of Rochester Medical Center, also has appointments in the departments of Biomedical Engineering and Neurobiology and Anatomy at the university.