May 9, 2000 Sleep apnea is more common and severe in post-menopausal women, and is likely due to decreased levels of female hormones, say clinical researchers at the University of Toronto and St. Michael's Hospital.
Researchers compared the prevalence and severity of sleep apnea between 290 pre- and 400 post-menopausal women at the St. Michael's Hospital Sleep Laboratory. They measured neck size and obesity, the usual markers of sleep apnea, to determine if any differences in these variables could explain the differences in apnea prevalence and severity. They found that 47 per cent of post-menopausal women suffered from sleep apnea compared to 21 per cent of pre-menopausal women, and that the condition was more severe in the post-menopausal group. This study was unique in the relatively large size of its female population and its consistent use of sleep study data.
"Our study shows that the greater incidence and severity of sleep apnea in these older women cannot be attributed to the usual anatomical differences like neck circumference or obesity," says Dr. David Dancey, a lecturer in the Faculty of Medicine at U of T and a clinical research fellow in the sleep laboratory at St. Michael's Hospital. "We think the difference may be due to the lower levels of estrogen and progesterone caused by menopause."
The study's authors used age as an indicator of menopause. Women under 45 were classified as pre-menopausal while women over 55 were classified as post-menopausal, and any patients with a history of hormone supplementation or premature menopause were excluded. While the researchers did not specifically measure hormone levels, Dancey points to previous studies which have shown the median age of menopause is 51 and begins for most women at 47.
"Now that we know structural differences like neck size and obesity don't explain the observed differences in apnea prevalence and severity between these two groups of women, we can begin looking at whether or not hormone therapy will be helpful for these women," says Dancey, the study's lead author. This study was funded in part by the Ontario Thoracic Society and is being presented in abstract form at the 96th International Conference of the American Thoracic Society in Toronto, May 5 to May 10, 2000.
Steven de Sousa
U of T Public Affairs
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