Adolescent health: Teens 'more depressed and sleeping less'
Adolescents are more likely to feel depressed and self-harm, and are less likely to get a full night's sleep, than 10 years ago, a study suggests.
Yet smoking, alcohol and anti-social behaviour - often linked to mental health problems - were less common for 14-year-olds in 2015 than in 2005.
Factors behind mental health problems may be changing, the University College London researchers said.
The rise in depressive symptoms was "deeply worrying", a charity said.
Researchers from London and Liverpool analysed data from two large cohorts of 14-year-olds - the first group from around Bristol, born in 1991-92, and the second from across the UK, born in 2000-01.
There were 5,600 young people surveyed in the first group and 11,000 in the second.
In 10 years, based on a standard questionnaire on mood and feelings, levels of depression in this age group rose from 9% to 15%.
Adolescents who said they had hurt themselves on purpose rose from 12% to 14%. The rate of increase was similar for boys and girls, although girls are more likely to self-harm.
While obesity and poor body image also rose, fewer 14-year-olds in 2015 had tried alcohol, binge drinking, smoking and having sex - compared with those surveyed a decade before.
They were also less likely to have tried cannabis or other drugs - 4.3%, down from 5%.
When it came to sleeping, the 2015 cohort were more likely to go to bed later and wake up earlier, meaning that more of them slept less than the recommended eight hours for teenagers.
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Dr Praveetha Patalay, associate professor at UCL and co-author of the study in the International Journal of Epidemiology, said the research gave a bigger picture of adolescent health, not only mental health in isolation.
"It's a holistic view, with some things getting worse and some improving.
"We have to remember that lots of things are changing for young people - in different directions."
She said that although the study could not pinpoint causes of mental health difficulties, it could be valuable in identifying what the risk factors are for mental health problems.
In her early teenage years Lauren Nicole Coppin Campbell, now 21, began to suffer with body image and low self-esteem.
For her, the images of people she was seeing on social media and in popular culture had a negative impact.
"I didn't feel like the people I was seeing on my feed we're representative of me.
"You rarely saw curvy, chubby, black women or girls who were being portrayed as beautiful or intelligent.
"On social media or other media you often see stereotypes - the bigger woman is the comedian, the funny person you laugh at or who you feel sorry for."
Before she was 16, she began forcing herself to be sick in a bid to obtain what she calls a "twisted image of perfection."
At times it felt like there was no escape.
"It isn't just online," she added.
"You can go to school or see friends on the weekend and they might start talking about Kylie Jenner or whoever else who may make you feel you're lesser than."
Lauren is now working as a plus size model and is an ambassador for The Be Real Campaign.
Emma Thomas, chief executive of charity YoungMinds, said the rise in 14-year-olds self-harming or experiencing depressive symptoms was "deeply worrying".
"The factors behind mental health problems are often complex, but we know that stress at school, bullying, concerns about body image, and the pressures associated with social media can all have a big impact," she said.
"To make matters worse, it's often far too difficult for young people to get mental health support, which means that their problems can escalate unnecessarily."
Dr Bernadka Dubicka, chair of the child and adolescent faculty at the Royal College of Psychiatrists, said: "This study provides further confirmation that young people today are struggling with mental health problems more than their 90s counterparts.
"The sharp rise in levels of depression and the increase in self-harm are worrying, as are the concerns our young people have around their body image."