Some women may have more or fewer asthma symptoms, such as coughing and wheezing, depending on their time of the month, according to a Norwegian study.
Researchers, whose findings appear in the American Journal of Respiratory and Critical Care Medicine, said spikes and dips in estrogen and other hormones likely affect the lungs and other physiological responses involved in breathing.
However, it's still unclear whether the results could improve doctors' treatment of women with asthma.
"Respiratory symptoms varied significantly during the menstrual cycle," wrote lead researcher Ferenc Macsali of Haukeland University Hospital in Bergen, Norway, and colleagues.
Other researchers said that while scientific studies have come to competing conclusions, anecdotal evidence does show variations for some patients during their menstrual cycles, which Samar Farha at the Cleveland Clinic described as "a very important cycle... with all the biological changes and physiological things that happen.
"(Some) asthmatics describe that just before their menses, they get a worsening of their symptoms," Farha, who studies asthma and other respiratory diseases but wasn't involved in the study, told Reuters Health.
The researchers surveyed close to 4,000 women in Northern Europe who had normal periods and weren't taking birth control pills. Along with other health and lifestyle questions, they asked women to report when their last period started, as well as whether they'd had any breathing-related problems in the past three days, such as wheezing or waking up with a coughing attack.
Just under eight percent of women in the study had been diagnosed with asthma. Between two and six percent reported recent wheezing, coughing and/or shortness of breath. The researchers found that the number of women with each of those symptoms changed depending on where they were in their menstrual cycle.
For example, wheezing spiked just before and after mid-cycle, which is when they ovulate. The dip in between corresponds to peaks in estrogen, follicle stimulating hormone and luteinizing hormone.
Complaints of shortness of breath and coughing both declined just after women got their periods, and shortness of breath was also more rare right before menses started. Macsali's team saw cyclical patterns in breathing symptoms in women with and without asthma. What explains those patterns is still up for debate.
Estrogen may affect the lungs directly, the researchers said. Insulin resistance and markets of general inflammation are known to vary during the menstrual cycle, which could also play a role in when breathing symptoms