Endometriosis and oral contraceptive use are associated with a higher risk of asthma in women of reproductive age, according to a new study.

These results were presented at the recent 2018 American Thoracic Society (ATS) International Conference in San Diego, California.

The lead investigator, Joe Zein, MD, with the Cleveland Clinic’s Respiratory Institute, conducted the study with a research grant from the National Heart, Lung, and Blood Institute (NHLBI).

Zein was awarded the NHLBI grant to study sex differences in severe asthma. His latest findings provide more evidence for connections between asthma and sex hormones.

Findings — from the analysis of a national database comprising 3,272,020 women, ages 20 to 40 — showed that asthma was more prevalent in women with endometriosis (23.8 percent) than those without this disease (13.2 percent), across weight groups and categories.

Researchers later replicated these results using the National Health and Nutrition Examination Survey.

“Our epidemiological studies continue to support a link between sex, sex hormones and asthma,” Zein said in a press release. “This finding is further confirmation of our efforts to pinpoint the linking mechanisms so that we can one day develop appropriate treatments.”

Another study led by Zein — based on database records of 6.5 million women between 20 to 50 years old, asthma was seen to be more prevalent in those using oral contraceptives (14.3 percent) than those not (8.8 percent) after adjusting for race, body mass index (BMI), smoking status and age.

“Until we discern the exact linking mechanisms, this research can allow sex and factors impacting sex hormones to inform our treatment decisions for women with asthma,” Zein added.

In earlier work, Zein had found that lower testosterone and progesterone levels in men and low testosterone combined with higher estradiol levels in women were associated with poorer lung function.

Asthma is generally more prevalent in boys than girls between ages 4 to 14, 11.5 versus 9.9 percent, respectively. But after puberty these numbers switch, with asthma becoming more prevalent and severe in women. After menopause, asthma’s intensity switches again, becoming more severe in older men.

Zein’s research is reported to be the first to demonstrate that menopause could have a protective effect against asthma severity in women.