Children who are sexually abused or raped are three times more likely to grow up to be gay or bisexual, a controversial new Christchurch study shows.
But gay leaders have questioned whether anything could "cause" people to be gay.
Otago University researcher associate professor Elisabeth Wells has looked at the connection between adverse childhood events and sexuality and found those who experienced trauma were significantly more likely to be non-heterosexual.
The study used results from the New Zealand Mental Health Survey, which surveyed almost 13,000 people aged over 16 between 2003 and 2004.
Participants were asked whether they thought of themselves as bisexual, heterosexual or homosexual and if they had same-sex sexual experiences or relationships.
Less than one per cent of people identified themselves as homosexual, but three per cent had a same-sex encounter.
Wells said the more "adverse events" experienced in childhood – including sexual assault, rape and domestic violence – the more likely the person identified with one of the non-exclusively heterosexual groups.
She said most people from disturbed backgrounds were heterosexual.
However, the study showed a clear relationship between negative events in childhood and homosexual or bisexual relationships later in life.
Of those who reported sexual abuse or rape in childhood, about 15 per cent were non-heterosexual. Of those who had not had these experiences only five per cent were non-heterosexual.
"One possibility is that it basically comes from the sexual assault or rape and that makes people think about having sex with someone of the same sex," said Wells.
New Zealand Aids Foundation (NZAF) community engagement co-ordinator Hamish Milne and Canterbury gay youth group Q-topia administrator Anne Nicholson said they did not look for "events" that made them gay just like they did not look for events that made straight friends straight.
"I know people who have been abused and are gay and haven't been abused and are gay; it's not something a study can say that it's why a certain group of society is gay," said Nicholson.
Sexuality was "fluid" and she could not be sure she would still be a lesbian in 20 years time.
Milne said there was growing evidence of negative health outcomes for gay and bisexual people, such as higher rates of mental illness.
It was possible that gay people were also at higher risk of suffering abuse or rape as children, which would be a concern, he said.
NZAF director prevention and communication, Simon Harger-Forde, urged caution when reading the study, which he said used Mental Health Survey data in a way that was not intended.
There was no evidence that people who were gay tended to come from more disturbed backgrounds.
Studies like this could increase discrimination and prejudice against homosexuals, he said.
Christchurch GP and sexual-assault clinician Clare Healy said the results were no surprise.
Sexual assault, rape and domestic violence were about power, fear and intimidation, she said.
"As we grow up, we seek solace, comfort, nurturing relationships, and it doesn't surprise me that someone who has suffered abuse from one sex might seek these things by exploring a same-sex relationship during their lifetime," said Healy.
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