Depending on the measure, HRT recipients on average did anywhere from 10 to 30 per cent worse on hearing tests than women who had not received HRT, reported Dr Robert Frisina from the University of Rochester Medical Center at a medical meeting this week.
The findings are the latest to reveal the negative effects of HRT, which are forcing women to turn to alternative options, such as natural plant oestrogens, to treat menopause symptoms and protect against osteoporosis risk later in life.
Other scientists have previously linked HRT to increased risk of breast cancer, heart attacks, stroke, and dementia, and with each study showing the treatment's risk, natural ingredient manufacturers saw a peak in demand. In the last year Israeli soy isoflavone supplier Solbar has seen growth of around 30 per cent in isoflavone sales in Europe. Dutch firm Acatris also reported similar benefits to its soy product sales in 2003.
The Rochester team used three tests to compare the hearing of 32 women between the ages of 60 and 86 who had had hormone therapy to 32 other women who had not. While the HRT group performed more poorly across the board, it was in complex settings - such as the ability to decipher a sentence while listening to someone amid a loud backdrop - that the HRT group fared worst.
Frisina called the results 'very surprising'. "We thought hormones would help women hear better because of the presence of oestrogen receptors in the ear. This is the opposite of what we were expecting."
The HRT group performed most poorly on a test aimed at measuring not just how well the ear actually detects a sound, but also how well the brain processes that information. A large portion of age-related hearing loss, called presbycusis, involves the brain's faltering ability to process information.
This sophisticated system decreases as we get older, said the researchers, and it is this ability that is most diminished in women who have received HRT compared to women who have not. Women in the HRT group on average performed this task 30 per cent less effectively than other women.
"The most obvious situation is a party where a lot of people are talking, and you're trying to listen to one particular person. It's as if the aging process, when it comes to their ability to hear, was accelerated in these women," said Frisina.
"It's important to alert women that there could be another significant side effect of hormone-replacement therapy," he added. "We know these findings clearly apply to the 64 women we studied. What we can't say, from such a small number of people, is the extent to which they apply to everyone. A much larger study needs to be done."
The findings will be submitted to a journal for publication.