Teens and young adults, who recently had unprotected vaginal sex, have higher tendency to engage in heterosexual anal sex, says a new study.

The findings of the research by researchers at the Bradley Hasbro Children's Research Center reflect recent data indicating that anal sex rates among adults doubled between the years 1995 and 2004.

Being one of the first of its kind, the study has highlighted the little-known factors linked with heterosexual anal intercourse among adolescents and young adults.

"The topic of anal intercourse is often considered taboo - especially when discussed in the context of youth relationships - even though we know that this behavior is a significant risk factor for HIV and other sexually transmitted infections. It's critical that we recognize that more and more young people are engaging in anal sex so we can open the lines of communications and help them protect their sexual health," said lead author Celia Lescano, PhD, of the Bradley Hasbro Children's Research Center (BHCRC).

In the study, the scientists examined sexual behaviour of 1,348 adolescents and young adults between the ages of 15 and 21 who had unprotected sex in the previous three months.

It was found that 16 percent had engaged in heterosexual anal intercourse within the timeframe, with condoms being used just 29 percent of the time.

Females who had heterosexual anal sex were more likely to be living with their partners, to have two or more sexual partners and to have previously experienced coerced intercourse.