Girls at mixed-sex schools feel more under pressure to be thin and have lower self-esteem than those at girls' schools, a study has found (file photo)

Girls at mixed-sex schools feel more under pressure to be thin than those at all-girls' schools, a study has found.

They were also more likely to feel pressure to be thin and have lower self-esteem, it was revealed.

The presence of boys may make girls worry more about how they look, researchers said.

On the other hand, an all-female environment may protect young women from negative messages about body image, they added.

The team, from the University of Bristol, wanted to investigate the factors that contribute to a young woman's confidence.

Society 'continues to advocate an unrealistically thin body shape' and girls being aware of this pressure - and acting on it - is 'increasingly concerning', they said.

They wanted to find out if the type of school a young woman attends affects her self-esteem - something they said was 'largely unexplored' before their study.

As part of their research, they recruited 212 British girls with an average age of 13.8 attending either a single-sex or co-educational (mixed sex) school in West Sussex, south east England.

The schools were broadly similar in socioeconomic terms, and school uniform was compulsory at both.

The girls were given questionnaires which asked them for their height and weight, and their Body Mass Index was calculated from the results.

The questionnaires also asked about their attitudes to appearance and weight; whether they were currently trying to lose weight, and, if so, by what method.

They were also quizzed about their self-esteem and their social support network.

Despite the majority - 79 per cent - of the girls having a normal BMI, researchers found 46 per cent were trying to lose weight.

Some 23 per cent were doing this through dieting; 41 per cent by exercising and 1 per cent by smoking.

While there were few differences between the two schools, women in the same-sex one were more likely to take pressures to be thin to heart.

The presence of boys may inflate girls' worries about how they look, lowering confidence, researchers said

The presence of boys may cause women to care more about how they look - lowering their confidence, researchers said.

Writing in the report, lead author Victoria Cribb, of the University of Bristol, said: 'Internalising the thin ideal portrayed by the media has a stronger link with self-esteem in girls attending a co-educational school.

'Greater internalisation is linked to lower self-esteem in girls in mixed gender environments.'

The study supports the argument that the presence of boys inflates girls worries about their looks, lowering self-esteem, she added.

Meanwhile, in same sex schools, women may be protected from taking cultural attitudes about women being thin to heart - meaning it doesn't affect their confidence as much.