Women who take HRT to help them cope with symptoms of the menopause could face an increased risk of deafness, a landmark US study suggests.
The research on more than 80,000 women found that those who took hormone replacement therapy for between five and ten years had a 15 per cent higher risk of hearing loss.
And those who took it for longer had a still greater chance of suffering from deafness, the mass study found.
Scientists said it was not clear why the pills were linked to a higher chance of hearing loss.
Some studies had previously suggested the therapy could protect hearing, as oestrogen influences the auditory pathways.
The findings, from the North American Menopause Society, also unexpectedly found that women who had a late menopause were more likely to suffer hearing problems – with a 10 per cent higher risk among women who were above the age of 50 when they entered “the change”.
The study – believed to be the first large prospective study to examine the links between menopausal onset and risk of hearing loss – did not prove that age or hormone therapy caused the increased risk of deafness, as the research was observational. But other studies in animals have shown that administration of the hormones oestrogen and progesterone can worsen hearing.
After reviewing self-reported hearing loss in 80,972 women, researchers found that the use of oral HRT for long periods was linked with a higher risk of hearing loss.
Writing in the journal Menopause, they said women considering taking HRT should consider the risk of hearing loss when weighing up the risks and benefits of the treatment.
Doctor JoAnn Pinkerton, executive director of the North American Menopause Society (NAMS), said: “Information about the potential effect on hearing is important to include in a discussion regarding the risks and benefits of hormone therapy for symptomatic menopausal women.”
HRT is used to treat uncomfortable symptoms of the menopause – such as hot flushes, migraines, disrupted sleep, mood changes and depression – by topping up the decreased levels of hormones produced by the body.
Last year a study found the treatment – which can be given as pills or patches – could triple the risk of breast cancer.
It came after the National Institute of Health and Care Excellence changed guidance to encourage more doctors to prescribe HRT, warning that too many menopausal women were suffering in silence.
But doctors were reluctant to prescribe it after a study in 2002 suggested it could raise the risk of cancer, a claim which was later widely debated. In 2000 more than 6 million prescriptions were isseud for the treatment, but since then the number has more than halved.
Other findings have been far more positive.
Last month research suggested the therapy could reduce the risk of early death by as much as 30 per cent, improving heart health.