Women who have irregular menstrual cycles - those that are longer or shorter than average - may be at higher risk for some heart problems, a new study suggests.

The study, published in the Journal of the American Heart Association, found women whose cycles were outside the typical 22- to 34-day range faced a higher cumulative risk for conditions such as coronary heart disease, heart attacks and atrial fibrillation than their peers whose cycles fell within that range.

Having a regular menstrual cycle length - the time from the first day of a period to the first day of the next period - indicates hormone systems connecting the hypothalamus, pituitary gland and ovaries are functioning properly, which is an important indicator of overall health. Research shows about 20% of women experience irregular cycle lengths.

Previous studies have found a link between irregular menstrual cycles and heart disease risk factors such as insulin resistance, high cholesterol, high blood pressure, chronic inflammation and polycystic ovarian syndrome. Some studies suggest hormonal fluctuations in the menstrual cycle place women at higher risk for arrhythmias, or irregular heartbeats.

But “the association between menstrual cycle characteristics and adverse cardiovascular outcomes remains unclear,” senior author Dr. Huijie Zhang said in a news release. “Considering the increasing prevalence of heart disease - with 45% of women in Western countries affected - and related mortality, there is a need to explore these risk factors.”

The study investigated whether menstrual cycle length was associated with overall heart disease and specific cardiovascular events in 58,056 women enrolled in the U.K. Biobank, a large health database in the United Kingdom. The women, who had not begun menopause and who had no cardiovascular disease at the start of the study, were an average 46 years old. Health data was collected in follow-up visits from 2006 to 2019.

Over a median 11.8 years of follow-up, the researchers found women with irregular cycles had a 19% greater risk of cardiovascular disease - which included coronary heart disease, heart attack, a type of arrhythmia called atrial fibrillation, stroke and heart failure - compared to those with regular-length cycles. In terms of menstrual cycle length, if a woman’s cycle was shorter, cardiovascular disease risk increased by 29%. If her cycle was longer, risk rose 11%.

Risk differed when researchers looked at shorter and longer cycles separately for each condition. For example, shorter cycles were associated with a 38% higher risk for AFib, while women with longer cycles had a 30% increased risk for the condition. However, menstrual cycle length was not associated with an increased risk for stroke or heart failure.