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Late nights and lie-ins at the weekend are bad for your health

By Linda Geddes

Hitting the snooze button at weekends to make up for early starts during the week may be doing more harm than good. Social jetlag – which occurs when your work and social commitments conflict with your innate desire to sleep at certain times – may increase your risk of heart disease.

Social jetlag is similar to the tiredness people feel when travelling from one time zone to another, but has a different cause. “A lot of people will be waking up at 7 am on weekdays, but going to bed later and sleeping in on the weekends to compensate,” says Sierra Forbush at the University of Arizona in Tucson.

To investigate the effects of social jetlag, Forbush’s team analysed data from 984 adults living in Pennsylvania, US. To calculate how much social jetlag they experienced each week, Forbush compared the midpoints between when people said they went to bed and woke up on weekdays and weekends. She also adjusted for how long people slept each week, and whether they suffered from insomnia.

The team found that for every hour of social jetlag, there was an 11 per cent increase in the likelihood of a person having cardiovascular disease. Social jetlag was also linked to worse mood and increased sleepiness and fatigue.

One hour effect

People who experienced just a single hour of social jetlag each week – equivalent to going to bed at midnight and waking at 8 am at weekends, and 11pm and 7am on weekdays – were 22 per cent more likely to rate their health as good, rather than excellent, and 28 per cent more likely to rate it as fair or poor.

“Physicians often tell people to think about their diet and exercise, but I think this offers an additional preventative strategy,” says Forbush, whose results were presented at the SLEEP meeting in Boston this week. “It’s not just about getting enough sleep, but getting regular sleep: ideally you want to be going to bed and waking up at the same time every day of the week.”

This isn’t the first study linking social jetlag to poorer health. Almost all the hormones in your body are under circadian control, and frequently shifting your sleep and wake times may cause them to fall out of synch. “There are studies indicating that chronotype – a person’s biological inclination towards morning or evening preference – may influence risk of cardiovascular disease, and evening types may be more at risk,” says Tami Martino, of the University of Guelph in Ontario, Canada.

In a separate study, also presented at the meeting, Dorothee Fischer of the Harvard T.H. Chan School of Public Health showed that people living towards the western side of US time zones are more likely to be evening types – probably because the sun rises later.

Indeed, for every degree you move west, people shifted about two minutes later, making the average difference between an eastern state like Maine and a western one like Indiana – both within the Eastern time zone – approximately 40 minutes. There may also be higher levels of social jetlag, on average, in such westerly states, Fischer says.

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