This finding is demonstrated in a new analysis of the Nurses’ Health Study II.
“To date, several studies have reported increased risks of cardiovascular risk factors or cardiovascular disease in connection with cycle disorders,” Yi-Xin Wang, MD, PhD, a research fellow in nutrition, and associates from the Harvard School of Public Health, Boston, wrote in an article published in JAMA Network Open.
Ute Seeland, MD, speaker of the Gender Medicine in Cardiology Working Group of the German Cardiology Society, said in an interview“We know that women who have indicated in their medical history that they have irregular menstrual cycles, invariably in connection with polycystic ovary syndrome (PCOS), more commonly develop diabetes and other metabolic disorders, as well as cardiovascular diseases.”
Cycle disorders’ role
However, the role that irregular or especially long cycles play at different points of a woman’s reproductive life span was unclear. Therefore, the research group investigated the associations in the Nurses’ Health Study II between cycle irregularity and cycle length in women of different age groups who later experienced cardiovascular events.
At the end of this study in 1989, the participants also provided information regarding the length and irregularity of their menstrual cycle from ages 14 to 17 years and again from ages 18 to 22 years. The information was updated in 1993 when the participants were aged 29-46 years. The data from 2019 to 2022 were analyzed.
“This kind of long-term cohort study is extremely rare and therefore something special,” said Dr. Seeland, who conducts research at the Institute for Social Medicine, Epidemiology, and Health Economics at the Charité – University Hospital Berlin.
The investigators used the following cycle classifications: very regular (no more than 3 or 4 days before or after the expected date), regular (within 5-7 days), usually irregular, always irregular, or no periods.
The cycle lengths were divided into the following categories: less than 21 days, 21-25 days, 26-31 days, 32-39 days, 40-50 days, more than 50 days, and too irregular to estimate the length.
The onset of cardiovascular diseases was determined using information from the participants and was confirmed by reviewing the medical files. Relevant to the study were lethal and nonlethal coronary heart diseases (such as myocardial infarction or coronary artery revascularization), as well as strokes.
Significant in adulthood
The data from 80,630 study participants were included in the analysis. At study inclusion, the average age of the participants was 37.7 years, and the average body mass index (BMI) was 25.1. “Since it was predominantly White nurses who took part in the study, the data are not transferable to other, more diverse populations,” said Dr. Seeland.
Over 24 years, 1,816 women (2.4%) had a cardiovascular event. “We observed an increased rate of cardiovascular events in women with an irregular cycle and longer cycle, both in early an in mid-adulthood,” wrote Dr. Wang and associates. “Similar trends were also observed for cycle disorders when younger, but this association was weaker than in adulthood.”
Compared with women with very regular cycles, women with irregular cycles or without periods who were aged 14-17 years, 18-22 years, or 29-49 years exhibited a 15%, 36%, and 40% higher risk of a cardiovascular event, respectively.
Similarly, women aged 18-22 years or 29-46 years with long cycles of 40 days or more had a 44% or 30% higher risk of cardiovascular disease, respectively, compared with women with cycle lengths of 26-31 days.
“The coronary heart diseases were decisive for the increase, and less so, the strokes,” wrote the researchers.