Having irregular or extra-long menstrual cycles could be a signal of an early death, according to a study.
Researchers have uncovered the link after studying the menstrual cycle of more than 90,000 women over two decades.
Women whose periods fluctuated were up to a third more likely to die of any cause over the course of the study.
Doctors believe it could be because women with irregular periods have underlying health conditions which have not been spotted.
Polycystic ovary syndrome (PCOS), which can cause irregular periods, is believed to be caused by insulin resistance – a risk factor for type 2 diabetes and heart disease.
But the Harvard University study, which has yet to be published, did not investigate the exact link between premature death and periods.
The findings, presented at the American Society for Reproductive Medicine’s 75th Scientific Congress and Expo in Philadelphia, only found a correlation.
Irregular periods are defined as periods which come early, or late, without a regular pattern.
The average menstrual cycle lasts 28 days. Women bleed for five days on average – but it is normal for it to be a bit shorter or longer than this, the NHS says.
Researchers analysed data on 93,775 women – who came from a variety of ages – between 1991 and 2013.
Participants had described the history of their menstrual cycles, reporting the usual length and regularity.
They did this at ages 14 to 17, 18-22, and 28-48. The women had no history of cancer, diabetes or cardiovascular disease at enrollment.
Researchers accounted for relevant mortality risks, including BMI, race or ethnicity, physical activity and lifestyle factors.
During an average of 18-year follow up, 1,679 deaths were recorded including 828 from cancer and 166 from cardiovascular disease.
Abnormal menstrual cycle characteristics, such as irregularity and long cycle length, were linked to a greater likelihood of death.
Women whose menstrual cycles were always irregular between the ages of 18 to 22 were 34 per cent more likely to die from any cause over the course of the study than women reporting very regular menstrual cycles.
Between 14 and 17, women with irregular periods had 21 per cent higher odds of an early death.
A similar pattern was seen in women with irregular menstrual cycles from age 28 to 48, but the figure was not made clear in the study abstract.
Women whose cycle lengths lasted 32-39 days or more than 40 days faced a 23 and 28 per cent greater risk of death, respectively.
A menstrual cycle of more than 32 days in women aged between 28 and 48 years appeared to have an elevated risk of death by cancer and cardiovascular problems – such as heart disease, according to the researchers.
Dr Hugh Taylor, the ASRM’s vice president, said: ‘Irregular cycling could be evidence of an underlying health condition.
‘But these clues are subtle and may not, in themselves, cause much worry.
‘Patients who experience menstrual irregularity should be advised to maintain a healthy lifestyle and be alert to health changes.’
Endometriosis, pelvic inflammatory disease or thyroid problems are just some of the conditions that can cause irregular periods.
Polycystic ovary syndrome (PCOS), which is thought to affect up to one in five women, is the one of the most studied.
Deborah Lawlor, professor of epidemiology at Bristol Medical School, told MailOnline there are plenty of studies showing the link between irregular periods and disease.
She said: ‘I have not personally done research in this area but I do know there is a very long history of papers showing an association between menstrual cycle irregularity and type 2 diabetes and cardiovascular disease.
‘The theory is that the irregular or long cycles reflect polycystic ovarian syndrome, or a tendency to it, which is thought to relate to insulin resistance and, or, they reflect overall lifetime lower oestrogen levels.
‘Seeing an association with mortality does not seem that odd to me. Whether any of these associations are causal is unknown.’
Health officials state there is no need to seek medical advice if your periods have always been irregular.
However, it may be worth seeing a doctor if there are sudden changes.