By Katie Hunt, CNN

Doctors should pay more attention to women's menstrual cycles and treat them as an additional vital sign to assess a patient's health, researchers have said, after a new study found a link between irregular periods and a greater risk of early death.

A team of mostly US-based researchers found that women who reported always having irregular menstrual cycles experienced higher mortality rates than women who reported very regular cycles in the same age ranges. The study took into account other potentially influential factors, such as age, weight, lifestyle, contraceptives and family medical history.

The study assessed 79,505 women with no history of cardiovascular disease, cancer or diabetes. The women reported the usual length and regularity of their menstrual cycles at three different points: between the ages of 14 to 17, 18 to 22, and 29 to 46 years. The researchers kept track of their health over a 24-year period.

"This study is a real step forward in closing the data gap that exists in women's health. It raises many interesting research questions and areas of future study," Dr. Jacqueline Maybin, a senior research fellow and consultant gynecologist at the University of Edinburgh's MRC Centre for Reproductive Health, told the Science Media Centre in London.

"These data will encourage future interrogation of menstrual symptoms and pathologies as an indicator of long-term health outcomes and may provide an early opportunity to implement preventative strategies to improve women's health across the lifespan," said Maybin, who wasn't involved in the research.

Irregular and long menstrual cycles have been associated with a higher risk of major chronic diseases including ovarian cancer, coronary heart disease, Type 2 diabetes and mental health problems, the study said.

In particular, the research, which published in the BMJ medical journal Wednesday, found that women who reported that their usual cycle length was 40 days or more at ages 18 to 22 years and 29 to 46 years were more likely to die prematurely -- defined as before the age of 70 -- than women who reported a usual cycle length of 26 to 31 days in the same age ranges.

The links were strongest for deaths related to cardiovascular disease than for cancer or death from other causes.

The authors were from the Harvard T.H. Chan School of Public Health, Harvard Medical School, Michigan State University and Huazhong University of Science and Technology in Wuhan, China.

No cause for alarm

Experts said that women who experience irregular or long menstrual cycles shouldn't be alarmed by the findings of the study. Maybin said it's important to remember that irregular menstruation is likely a symptom, not a diagnosis.

"A specific underlying cause of irregular menstruation may increase the risk of premature death, rather than the irregular bleeding, per se. We already know that women with polycystic ovarian syndrome (PCOS), a leading cause of irregular periods, have an increased risk of diabetes, high blood pressure and cancer of the womb. It is important that women with PCOS speak to their doctor to reduce these risks," she said.

The study was observational and can only establish a correlation, not a causal link, between an irregular or long menstrual cycle and premature death. Other unmeasured factors could have influenced the results.

Maybin noted that the participants in the study were all registered nurses. Shift work, particularly nightshifts, has been shown to have a significant impact on long-term health. Abigail Fraser, a reader in epidemiology at the University of Bristol, said that the study didn't appear to take in account socioeconomic status.

The study had some limitations, since the participants had to rely on their own recall of their menstrual cycles, which may not have been completely accurate, the researchers said.

However, the authors said in a news statement that studies such as this one "represent the strongest evidence possible for this question" because menstrual cycles can't be randomized.

An additional vital sign

Guidance issued in 2015 from the American College of Obstetricians and Gynecologists said that medical practitioners should treat the menstrual cycle in adolescents as an additional vital sign.

Like temperature and pulse rate, it should be used to assess a patient's overall health, and doctors should try to identify abnormal menstrual patterns in adolescence. This new study suggested that this should apply to all women during their reproductive lives.

"The important point illustrated by this study is that menstrual regularity and reproductive health provides a window into overall long term health," said Dr. Adam Balen, a professor of reproductive Medicine at Leeds Teaching Hospitals in the UK and the Royal College of Obstetricians and Gynecologists' spokesperson on reproductive medicine.

"Young women with irregular periods need a thorough assessment not only of their hormones and metabolism but also of their lifestyle so that they can be advised about steps that they can take which might enhance their overall health," said Balen, who wasn't involved in the study.