NEW YORK (Reuters Health) ¿ People who start having sex at a younger or older than average age appear to be at greater risk of developing sexual health problems later in life, a new study suggests.

The findings, according to researchers, cast some doubts on the benefits of abstinence-only sexual education that has been introduced in US public schools. Using data from a 1996 cross-sectional survey of more than 8,000 US adults, the researchers found that those who started having sex at a relatively young age were more likely to have certain risk factors for sexually transmitted diseases (STD) ¿ including a high number of sexual partners and a history of having sex under the influence of alcohol.

On the other hand, both "early" and "late" starters were at increased risk of problems in sexual function. This was true primarily of men, whose problems included difficulty maintaining an erection and reaching orgasm.

The findings are published in the American Journal of Public Health.

It's not clear from the survey why both early and late starters tend to have more sexual dysfunction, according to the researchers, led by Dr. Theo G.M. Sandfort of Columbia University in New York City.

But the findings, they write, "only partially support" abstinence-only sex education ¿ which encourages teenagers to save sex for marriage.

"Although our findings support an association between early initiation and long-term (STD) risk, they also suggest a more complicated picture of sexual functioning," Sandfort and his colleagues write.