According to a new US study, men who identify as heterosexual are three times more likely to classify bisexuality as “not a legitimate sexual orientation.”

This comes from a recent sociological survey from the University of Pittsburgh, which was carried out by the Public Health researcher, Mackey Friedman.

Dr Friedman explained that when a bisexual person feels that his or her sexual orientation is not recognised by their peers, it can cause the person to feel socially isolated and unable to talk openly with friends and family.

He said: “Bisexual men and women face prejudice, stigma, and discrimination from both heterosexual and homosexual people.

“This can cause feelings of isolation and marginalisation, which prior research has shown leads to higher substance use, depression and risky sexual behavior. It also can result in lower rates of HIV testing and treatment.”

As part of the study, Dr Friedman and his colleagues surveyed hundreds of adult university students for “words that come to mind” relating to bisexual people, such as “confused,” “different” and “experimental.”

The researchers then constructed a 33-question survey to share with an online sample of 1,500 adults.

The results of the survey, which was sponsored by the Indiana University Bloomington, were presented on Tuesday at the American Public Health Association’s 141st Annual Meeting & Exposition in Boston.

It showed that respondents were generally negative in their attitudes towards bisexual men and women, with almost 15% of the sample disagreeing that bisexuality was a legitimate sexual orientation.

Among those who had less prejudice against bisexual people were women, white people, and people who identified themselves as lesbian, gay, or bisexual.

However, those who identified as gay or lesbian also responded significantly worse towards bisexuality than those identifying as bisexual. Additionally, the survey found that it was male bisexuals who suffered more stigma than female bisexuals.

Dr Friedman added: “Having hard data to back up why a bisexual person might feel the need to be secretive about sexual orientation, something that can lead to higher depression and many other negative health outcomes, is very useful to people trying to fight stigma and marginalization.

“For example, this information can guide social marketing interventions and outreach to reduce that stigma, and improve rates of HIV prevention, testing and treatment within the bisexual community.”

According to a study from the Office for National Statistics (ONS), 1.5% of the adult population in the UK identify as gay, lesbian or bisexual, with younger people having a much higher representation than older groups.

In March, the University of Pittsburgh also found that people living with HIV are nearly 50% more likely to have a heart attack.