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04:29 - Source: CNN
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Women with irregular menstrual cycles or cycle lengths may face a higher risk of cardiovascular disease, a new study suggests.

Cycles that are shorter than normal – less than 21 days – and longer-than-normal cycles – at more than 35 days – were associated with a higher risk of cardiovascular disease and atrial fibrillation, or irregular heartbeats, according to the study, published Wednesday in the Journal of the American Heart Association. A menstrual cycle was measured as the number of days between each menstrual period.

Specifically, “long menstrual cycle length was associated with increased risks of atrial fibrillation but not myocardial infarction, heart failure, and stroke,” the researchers wrote, and shorter cycles were associated with a greater risk of coronary heart disease and myocardial infarction or heart attack.

Some questions remain.

While “women with menstrual cycle dysfunction may experience adverse cardiovascular health consequences,” the exact nature of that relationship and what’s driving it remains unknown, said senior study author Dr. Huijie Zhang, chief physician and professor at Nanfang Hospital of Southern Medical University in China, in an email.

Still, the study findings indicate that “it is time” to raise awareness around the importance of monitoring menstrual cycle characteristics throughout a person’s reproductive life, Zhang said.

Overall, about 14% to 25% of women have irregular menstrual cycles worldwide, according to the US National Institutes of Health.

The researchers, based in China, analyzed health data on 58,056 women in the United Kingdom. The women, ages 40 to 69, reported in questionnaires the length and regularity of their menstrual cycles over time and other medical information over the course of about 12 years.

Among the women, 39,582 reported having regular menstrual cycles, and 18,474 reported either irregular cycles or no periods.

The researchers found that 2.5% of the women with regular cycles developed cardiovascular disease, compared with 3.4% of those with irregular cycles.

Irregular menstrual cycles were associated with increased risks of cardiovascular disease despite other risk factors, such as “age, race and ethnicity, BMI, smoking status, drinking status, physical activity, history of oral contraceptive use,” the researchers wrote.

The data also showed that 0.56% of those with regular cycles developed atrial fibrillation, compared with 0.92% of those with irregular cycles.

And the researchers found that about 1.3% of those with regular cycles developed coronary heart disease, compared with 1.7% of those with irregular cycles. About 0.29% had heart attacks, compared with 0.45% of those with irregular cycles.

‘Another vital sign’

The findings came as no surprise to Dr. Stephanie Faubion, director of Mayo Clinic’s Center for Women’s Health and medical director of the North American Menopause Society.

“There’s accumulating evidence that irregular menstrual cycles are not healthy, and in fact, they could be considered another vital sign for women – and irregular menses should be triggering people to think about cardiovascular risk in women,” said Faubion, who was not involved in the new study.

Guidance issued in 2015 by the American College of Obstetricians and Gynecologists says that medical practitioners should treat the menstrual cycle in adolescents as an additional vital sign. Like temperature and pulse, it should be used to assess overall health, and doctors should try to identify abnormal menstrual patterns in adolescence.

Faubion said that studies have found an association between irregular menstrual cycles and markers for heart disease risk such as insulin resistance, high cholesterol, high blood pressure and chronic inflammation. Yet what’s behind these associations remain unclear.

“The exact mechanism behind it, we don’t know,” Faubion said, but menstrual cycles still should be considered a “marker” of overall health.

“And if you’re not menstruating on a regular basis, your health care professional should be looking into why you’re not menstruating on a regular basis,” she said. “Part of this is educating health care professionals that menstrual cycles are another vital sign for women.”

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More research is needed to better understand this association between cardiovascular health and the length and regularity of a menstrual cycle, said cardiologist Dr. Nieca Goldberg, medical director of Atria New York City and clinical associate professor of medicine at NYU Grossman School of Medicine, who was not involved in the new study.

She said in an email Wednesday that some studies have found an association between shorter menstrual cycles and insulin resistance and lipid abnormalities – but the reasons are elusive.

“Short cycles are associated with lower estrogen levels that affect lipid levels and insulin resistance. Atrial fibrillation risk may relate to hormonal changes and their influence on electrocardiograms,” Goldberg wrote. “It is clear that continued research in the area of menstrual cycle and cardiovascular risk is important for women and proves our work is not done in assessing risk factors for cardiovascular disease in women.”

CNN’s Madeline Holcombe and Katie Hunt contributed to this report.