Does this explain why teenagers are so lazy?

Teenagers are notorious for being impossible to drag from their beds in the morning.

But they actually do need a lie-in of up to 90 minutes longer in the morning, according to a scientific study.

US scientists have found teenagers have a later body clock, which makes them night owls, so that they go to bed late and wake up early.

The optimum bedtime for 17 and 18-year-olds is 12.30am, while they should wake up at 8.30am. That is compared to 60-year-olds, who are larks and typically go to bed at 11pm to rise an hour and a half earlier than teenagers at 7am.

The findings are based on data from almost 54,000 people from 2003 to 2014.

Teenagers have a later body clock, which makes them night owls, so that they go to bed late and wake up early, scientists have found

It is unknown why teenagers’ sleeping patterns make them sleep later, only to start getting up earlier around the age of 19. 

But the study states that blue light from smartphones and tablets may be affecting human circadian rhythms, while some experts say their habit of staying up late might also be changing their body clocks.

Men also sleep later than women up until the age of 40, perhaps because women’s lives are changing their sleeping patterns through less exposure to natural light as they take on the bulk of housework and childcare.

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Influenced by age and gender 

The researchers, whose study on sleeping patterns, or chronotypes, is published in the journal PLOS One, said: ‘The timing for optimal sleep can be as different as 10 hours among individuals, meaning that opposite chronotypes could share a bed without knowing that they do.

‘What chronotype you are, is influenced by age and gender – on average, older people are earlier chronotypes than younger people and women are earlier chronotypes than men during the first half of their lives.’

The optimum bedtime for 17 and 18-year-olds is 12.30am, while they should wake up at 8.30am

How was the study carried out? 

The researchers, led by Harvard T.H. Chan School of Public Health, looked at the hours people slept on weekend days, when an alarm clock or job were less likely to disrupt their natural sleeping times.

Their findings are based on self-reported sleeping times from 53,689 people involved in the American Time Use Survey.

What did they find? 

They found a 90-minute difference in the chronotype, or mid-point of sleep, between people aged 17 and 18 for whom it was 4.30am and people aged 60 whose mid-point was 3am.

ARE MOBILE PHONES RESPONSIBLE?

Cell phones are wreaking havoc on teenagers’ sleep patterns, a study warned in October.

Adolescents have never had such poor sleep: they sleep less, wake up in the night more, and tend to be more sleepy in the daytime than previous generations.

According to research by University of Montreal, it is no coincidence that this is the most social media-dependent generation to date.

Researchers found the more teens spoke on the phone, texted and trawled social media before bed, the worse their sleeping patterns were.

The worrying finding emerged just a week after the American Academy of Pediatrics loosened its guidelines on screen time for kids, saying we have to be ‘realistic’ – despite the health dangers. 

Although individuals’ sleep times vary, an average eight-hour night’s sleep would see the older age group go to bed at 11pm and rise at 7am, with teenagers an hour and a half later for both.

Women appear to wake earlier than men until the age of 40, when changing hormones may shift their sleeping patterns later.

But the study adds: ‘Differences in chronotype between females and males, as well as among different age groups, may also have non-hormonal causes, eg differences in family life (eg typically ‘female’ responsibilities such as household chores and childcare), work regimes (eg shift work) as well as somatic and mental disorders (eg depression), that may feed back onto the circadian clock via modification of internal bodily processes and/or light-dark exposure.’

Difference in sleeping patterns 

The difference in sleeping patterns which make up to 60 per cent of us night owls instead of larks, can reach 10 hours between different people.

Although highest in adolescents, it varies based on the amount of time people sleep, their working hours and responsibilities.

The difference has prompted previous calls for teens to be allowed to start school later in the day and the study concludes: ‘Our findings suggest that adolescents’ chronotypes are on average too late for school start times before 8.30am.’