Gay and bisexual men are at increased risk of acquiring the virus that leads to AIDS if they have mental health problems, according to a new study.

What's more, their risk of acquiring HIV increases with the number of mental health factors they report, researchers found.

Past studies have found that mental disorders, ranging from depression to substance abuse, are often seen among men with HIV, but “nothing about whether these factors predict HIV risk behaviors or becoming infected with HIV,” said study leader Matthew Mimiaga, from Harvard Medical School and Massachusetts General Hospital in Boston.

The Centers for Disease Control and Prevention (CDC) estimates that some 1.1 million people in the U.S. are living with HIV. About one case in six is undiagnosed. While the CDC says only about 4 percent of U.S. males have sex with other men, they represent about two-thirds of the country’s new infections.

Additionally, it’s known that the lesbian, gay, bisexual and transgender (LGBT) community also suffers from an increased burden of mental health problems.

When two health conditions tend to occur together in one population, researchers call them "syndemic."

For the new study in the Journal of Acquired Immune Deficiency Syndromes, the researchers looked at how five conditions - depression, alcohol abuse, stimulant use, multi-drug abuse and exposure to childhood sexual violence - affect men's risk of acquiring HIV.

They analyzed data on 4,295 men who reported having sex with men within the previous year. The participants were asked about depressive symptoms, heavy alcohol and drug use and childhood sexual abuse.

The participants did not have HIV when they entered the study between 1999 and 2001. They then completed a behavioral survey and HIV test every six months for four years.

Overall, 680 men completed the study. Those who reported the most mental health issues were the most likely to become HIV positive by the end of the study. They were also most likely to report unprotected anal sex and unprotected anal sex with a person who has HIV.

For example, compared to people without any of the five syndemic conditions, those with four or five had about a nine-fold increased risk of being infected with HIV by the end of the study.

The people with four or five mental disorders were also about three times more likely to have unprotected anal sex and about four times as likely to have unprotected anal sex with a person infected with HIV, compared to people without any mental health issues.

Mimiaga said that the next step is to look at how this information can be used to improve HIV prevention methods.

“We need to think about the fact that men who have sex with men in the U.S. have a high prevalence of these syndemic factors (which) for the most part get in the way of traditional HIV messaging or traditional HIV interventions,” he said. “These factors . . . are driving a lot of the risk and really need to be addressed in a comprehensive approach.”

Future research should also examine whether these mental disorders and behavioral risk factors create barriers to men getting treatment for HIV once they are infected, Mimiaga said.