There may be hope for heavy snorers and their bedfellows, as a recent study conducted by UW-Madison School of Veterinary Medicine scientists suggests that differences in gender hormones might heavily influence cases of sleep apnea in men and women.
Obstructive sleep apnea, which affects more than 18 million Americans, is a disorder found primarily in middle-aged men. It occurs when muscles that control the airway, especially the tongue, relax during sleep and block the flow of air. The person usually wakes up repeatedly throughout the night.
The researchers, Mary Behan, Andrea Zabka and Gordon Mitchell, wanted to see what role age plays in female rats’ responses to brief moments of oxygen deprivation, mimicking humans’ experience with sleep apnea, and compared their results to an earlier study on male rats’ responses.
“I expected a similar outcome in aging females, but it was quite striking that we found females and males are completely different,” Zabka said.
In the previous study, published last summer, researchers monitored male rats’ nerve activity from the brain to the tongue and diaphragm while depriving them of oxygen for short moments. They discovered that young and old male rats’ responses were totally different. Younger male rats had a much better protective response to oxygen deprivation than older male rats.
“Because in humans there are certain age-related problems in breathing that seem to be specific to males and females,” Behan said, “naturally we thought to do the exact same study on female rats.”
Zabka, Behan, and Mitchell began a new study with this in mind and found that, unlike the male rats, older females had an improved reaction to oxygen deprivation. Additionally, female rats showed an even better response to oxygen deprivation during one stage of their reproductive cycle.
“Perhaps, because of having higher levels of estrogen and progesterone, the nervous system of females adapts slightly differently, and adapts better with age,” Behan said.
“If you look at sections of the rats’ brains and look, particularly, for serotonin in old and young male and female brains, you can also see differences in the amounts of serotonin in the parts of the brain that are controlling nerves to the tongue,” she said.
In fact, when they depleted estrogen levels in female rats, mimicking the effects of menopause in humans, the researchers found less of the serotonin in certain areas.
“That suggests to us that gender hormones are very strongly involved in these kind of breathing disorders,” Zabka added.
Although the study did not directly focus on obstructive sleep apnea, the findings closely resemble data showing that middle-aged men are more likely to develop sleep apnea than middle-aged women. Studies also show that after women reach menopause — and their estrogen levels drop — cases of sleep apnea go up; however, if they are on hormone replacements, fewer women have sleep apnea.
People who suffer from sleep apnea often feel poorly rested in the morning and fatigued or drowsy during the day. In some cases, people may develop high blood pressure or other serious problems.
“If we continue in this line of research, perhaps in 10, 20 or 30 years we’ll see some therapeutic outcomes,” Behan said. “We’re very excited about what we have seen, but we’re a long way from being able to apply it to humans.”
