Almost a third of British teenagers feel ashamed of their body, with imagery of “idealised” bodies on social media driving their insecurity, new research has found.

The same number of young people have changed their eating habits in an effort to alter how they look, a survey of teenagers undertaken for the Mental Health Foundation (MHF) shows.

Experts said the results were alarming, particularly because body image anxiety can trigger self-harm and suicidal thoughts in teenagers.

The findings prompted calls for advertisements for weight loss and cosmetic surgery to be vetted and for social media firms to do more to prevent young people feeling bad about their bodies.

“Our survey has shown that millions of young people in Britain are worrying about their body image,” said Jane Caro, the foundation’s programme lead for families, children and young people. “Worries about body image can lead to mental health problems and, in some instances, are linked to self-harm and suicidal thoughts and feelings.”

Overall, 31% of 13- to 19-year-olds feel ashamed of their body shape, according to the YouGov survey of 1,118 British teenagers, which was weighted to represent everyone at those ages. Slightly more – 35% – had stopped eating or limited what they ate because they were worried about their body.

In addition, 35% of respondents worried about their body often or every day , 37% felt upset and ashamed about it and 40% said remarks by friends had made them worry about their appearance. Two in five said pictures they had seen on social media had made them worry about their body.

Research has shown that people’s dissatisfaction with their appearance often stems from comparing themselves unfavourably with others. The MHF said: “Exposure to idealised bodies in the media and social media provides significant risk of this and of internalising an ‘ideal’ body image that is unrealistic or unattainable.”

Experts in children’s mental health believe social media is a key factor in the growing numbers of teenagers needing care because they have anxiety and/or depression or they self-harm. The number of teenagers needing hospital treatment after trying to kill themselves has soared during the last decade, especially among girls.

“These alarming results show what a significant issue body image is for many young people. While social media can have lots of positives, it’s clear that regularly seeing images of ‘perfect’ bodies can heighten anxieties that young people have about how they look.”, said Emma Thomas, the chief executive of Young Minds.

The MHF wants the Advertising Standards Authority to pre-vet broadcast advertisements that may damage someone’s view of their body, such as ads for cosmetic surgery and weight loss.

NHS England has called for social media firms to pay a levy to help fund mental healthcare for under-18s, to reflect the harmful impact their content can have.

“We know that appearance is one of the things that matters most to young people. These concerning findings not only lay bare the scale of the problem but also clearly point to where teenagers say the blame should lie,” said Claire Murdoch, its national director for mental health.

“While the NHS long-term plan is dramatically expanding mental health services to see hundreds of thousands more people, it is time for industry and wider society to listen and act when teenagers say loudly that idealised body images, driven by social media, is fuelling mental ill-health in their generation.”

Thomas said the forthcoming new relationships and health curriculum in state schools in England from September needed to help “young people learn to recognise that the images they see on social media may be heavily edited, curated highlights of people’s lives – and that unrealistic standards of ‘beauty’ are not achievable for most people”.

• In the UK, Samaritans can be contacted on 116 123 or email jo@samaritans.org. In the US, the National Suicide Prevention Lifeline is 1-800-273-8255. In Australia, the crisis support service Lifeline is 13 11 14. Other international suicide helplines can be found at www.befrienders.org.