Having a lie in is something many of us look forward to on a Saturday morning, following a hard week at work.
But dozing in bed to clock up on snooze could be bad for women – especially around their time of the month.
Scientists have found women who catch up on sleep on their days off may suffer from more severe period pain.
Japanese researchers surveyed 150 female university students about their sleeping and menstrual patterns.
They wanted to examine whether social jetlag could affect their premenstrual syndrome (PMS) symptoms, New Scientist reports.
Students were classed as having social jetlag if the middle point of their sleep was an hour later on their days off.
For instance, if someone sleeps from 11pm to 7am on workdays, the midpoint is 3am. But when they sleep from midnight to 10am at the weekend, the midpoint is 5am – giving a social jet lag of two hours.
WHAT ARE THE OTHER RISKS OF SOCIAL JETLAG?
It may seem like the perfect start to the weekend, but a Saturday morning lie-in could be very bad for your health.
Differences in sleep patterns between our work days and days off raise the odds of obesity, diabetes and even heart disease, research has suggested.
While lazing in bed occasionally will not cause any harm, weekend after weekend of late starts could seriously damage health, said experts in 2015.
The warning came from Medical Research Council scientists who analysed data on the health, weight, height and sleeping habits of more than 800 men and women aged 38.
The study, published in the International Journal of Obesity, paid particular attention to ‘social jet lag’, the mis-match between waking hours on work days and weekends.
It is calculated by taking the midpoint of a person’s sleep on work nights and comparing it to the midpoint of their sleep during days off.
More than three quarters of the participants were classed as having social jetlag because of their sleeping habits.
The researchers found the students who suffered from social jetlag experienced more pain and bloating during their periods.
Yoko Komada, who led the study, said behavioural changes were also worse among those who caught up on their sleep.
And the team in Tokyo found the symptoms worsened for the students who had the highest levels of social jetlag.
The Meiji Pharmaceutical University findings were published in the scientific journal Chronobiology International.
The researchers remain unsure as to why catching up on sleep at the weekends may lead to worse period symptoms.
However, some believe it may disrupt the body’s internal clock – known as the circadian rhythm.
It is believed the disruption of the rhythm may impact hormone cycles that regulate menstruation and inflammation.
Period pain, thought to affect the day-to-day lives of a fifth of women, occurs when the muscular wall of the womb tightens.
This triggers the body to release pain-triggering chemicals and prostaglandins, hormones that worsen the pain.
But scientists in recent years have begun to point their finger at inflammation for playing a much bigger role in period pain.
A University of California, Davis, study two years ago found women suffering period pain had higher levels of a protein linked to inflammation.