EDINBURGH, Scotland (Reuters) - Sex at least three times a week can make people look 10 years younger, according to a survey published on Wednesday. "It`s not a case of these people having more sex because they look younger, they actually look younger because they are having more sex in loving, stable relationships," said Dr David Weeks, a neuro-psychologist at the Royal Edinburgh Hospital. Weeks, whose survey took 10 years to complete, told Reuters: "Because these people are having a better sex life, they feel better about themselves and actually look younger." Weeks, an American, interviewed some 3,500 people from Britain, Europe and the United States after he placed an advertsiement in New Scientist magazine in 1988. His survey of young-looking participants found that on average, they had sex at least four times a week - twice as often as the average person. When the participants were "rated" by volunteers who tried to guess their ages, the men were assumed to be 12 years younger and the women 10 years younger than they actually were. How does making love tap the fountain of youth? The human body produces growth hormones and other chemicals like endorphins during sex that enhance the body and mind. A woman`s body during orgasm releases the hormone oxytocin, which affects emotional centres of her brain. Men who regularly stimulate their mate`s oxytocin are rewarded with warmer feelings of affection. Weeks stressed that a number of other factors such as diet and exercise also affect whether or not people look younger. And casual sex with different partners did not help prevent wrinkles. If anything, the stress and pressure made for premature ageing. Masturbation was a healthy alternative to sex but would not be as beneficial as copulation.