At a school reunion last summer, one former classmate looked 10 years younger than the rest of us. Someone finally asked his secret. "Three orgasms a week," he said, to laughter. Later we asked him if he was serious, and he referred to a study showing that, when all the various scientific claims for improving longevity are fed into one database, you gain two extra years by flossing every night and three years by having more than three orgasms a week. It went against all the negative folk wisdom we'd heard about how having too much sex could drain me of my "chi," bring on depression, or even lead to a stroke.

As it turns out, the benefits of sex are a factor in all three categories of male mortality – heart disease, cancer, and environmental causes (stress, accident, suicide) – and plenty of scientists are pushing the idea that the more sex you have the longer you'll live. The Johnny Appleseed of the theory is Michael Roizen, a 62-year-old doctor who chairs the Wellness Institute at the Cleveland Clinic.

"For men, the more the better," he says. "The typical man who has 350 orgasms a year, versus the national average of around a quarter of that, lives about four years longer." And more than those extra four years, Roizen says, the men will feel eight years younger than their contemporaries. Is there an optimal number of orgasms for the average man? Roizen suggests, with a straight face, that 700 a year could add up to eight years to your life. This is an ambitious prescription: The average American adult male has sex just 81 times a year.

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Roizen's formula may be new, but the benefits of sex and orgasms have been tracked for years, and there's some compelling hard evidence to back Roizen's claims. A Swedish study done in the '80s found that 70-year-olds who made it to 75 were the ones still having sex, and a Duke University study that followed 252 people over 25 years concluded that "frequency of intercourse was a significant predictor of longevity."

But the big kahuna of longevity studies was completed just 10 years ago in Wales. British scientists interviewed nearly 1,000 men in six small villages about their sexual frequency, then arranged for all death records to be forwarded so the scientists could record their life spans. Ten years later they determined that men who had two or more orgasms a week had died at a rate half that of the men who had orgasms less than once a month. "Sexual activity seems to have a protective effect on men's health," the researchers concluded.

Skeptics will tell you that these studies don't actually prove that people live longer because of sex. "Maybe healthier people have more orgasms, instead of the other way around," says Erick Janssen of the Kinsey Institute. His colleague Debby Herbenick points out that the Wales study failed to even ask whether the men were in relationships; science makes a strong case that good marriages improve men's longevity. "Studies are demonstrating that there are longevity health benefits to sex," says Beverly Whipple, professor emerita at Rutgers and co-author of the book 'The Science of Orgasm.' "But we can't say there's a definite cause and effect."

Which raises the question: What exactly is the science behind all these studies? An orgasm is a major neurological and physiological event (Alfred Kinsey once described it as "the expulsive discharge of neuromuscular tensions"). The bloodstream is flooded with hormones such as oxytocin and dehydroepiandrosterone (DHEA). At its height just a few minutes after ejaculation, oxytocin may increase bonding, leading people to fall in love, but it also reduces stress and brings on sleep. DHEA is actually a steroid and has been shown to reduce the risk of heart attack in middle-aged men. Both hormones have been shown to reduce depression.

Sex, even as little as once or twice a week, also increases immunoglobulin levels – the stuff in your blood that fights infection and disease – as much as 30 percent higher than in those who abstain.

Interestingly, most orgasm studies blur the line between sex and masturbation, referencing both as "sexual expression." Roizen believes masturbation is, at the very least, "a good supplement to monogamous sex," and prostate cancer rates have been proven to directly correlate to frequency of ejaculation. Scientists say ejaculating at least four times a week can reduce one's risk by up to 30 percent.

Although Roizen's 700 orgasms per year is unrealistic for most of us, research suggests that two to three orgasms a week will still yield benefits. And yet another study has shown that those having sex three times a week on average appear seven to 12 years younger than their actual ages. Remember that before your next high school reunion.