The latest study also pointed out that gay men and bisexuals are more susceptible to "psychological distress," and lesbians have a higher risk of poor or average health, as compared to other women.

This study mirrors its findings of previous research but it doesn't explain why gay, lesbians and bisexual people face that higher health risk. However, according to the researchers, it is the discrimination that causes stress and may be a reason why they feel distressed.

"Stigma and discrimination against the LGBT population can lead to lower levels of self-esteem and cause feelings of shame and rejection," explained study author Gilbert Gonzales, assistant professor with Vanderbilt University School of Medicine, in Nashville.

The study findings revealed that bisexual men had moderate to severe case of psychological distress. "We were surprised to find that bisexual adults were so much more likely to report psychological distress compared to their gay and straight counterparts," Gonzales said. He explains that it is possible that they suffer from anti-gay discrimination in society, in general as well as anti-bisexual bias within the gay community.

According to Brian Mustanski, an associate professor of LGBT issues at Northwestern University Feinberg School of Medicine in Chicago, it is the stigma attached to LGBT that plays a role. His research points out at bullying by others as the leading cause of depression.

Susan Cochran, professor of epidemiology at the University of California, Los Angeles, revealed that these findings are not unheard of. However, she added that risk of substance abuse doesn't mean that the person is guaranteed to suffer from it. "Being gay, lesbian or bisexual doesn't necessarily lead to this," she said.

Additionally, she said that sexual orientation also has a part to play. "For example, women who work are more likely to drink and white women are more likely to drink, but women raising small children are less likely to drink. So lesbians -- who are more likely to work, be white and not raising kids -- drink more," she said.