Quick quiz: Would you rather run 75 miles or have sex three times per week for a year? Research shows that both activities burn the same number of calories. (7,500, to be exact).

We often think that something that feels good can’t possibly be good for us. Now it’s time to think again.

Sex in a loving, intimate relationship has numerous health benefits. In women, for example, the sexual act triggers the release of oxytocin. Oxytocin promotes feelings of affection and triggers that nurturing instinct. In men, sex encourages the flow of testosterone, which strengthens bones and muscles and helps transport DHEA, a hormone that may be important in the function of the body’s immune system.

Paul Pearsall, Ph.D., author of Superimmunity, also maintains that sex in a loving relationship helps the immune system by increasing the flow of certain chemicals in the body.

Hugh O’Neill, editor of Men’s Health magazine, recently listed some health benefits of sex, as well. Regular sex is regular exercise and has similar benefits, including improved cholesterol levels and increased circulation. Men’s Health also reported that men who have sex at least three times each week may have a decreased risk of developing prostate problems.

Sex, like exercise, releases endorphins. Endorphins contribute to the runner’s high and diminishes pain levels.

An active sex life may help us live longer, too. Dr. David Weeks, a clinical neuropsychologist at Scotland’s Royal Edinburgh Hospital, conducted a study of 3,500 people ranging in age from 18 to 102. Weeks concluded that sex actually slows the aging process. (For more information, see Secrets of the Superyoung, by Dr. David Weeks)

Sexual therapists remind us that frequent sex is a form of exercise. And feeling secure in a relationship leads to feeling happier, which could lead to greater health…and a younger look.

In fact, these studies indicate that intimacy plays a key role in the health benefits of sex. A promiscuous sexual relationship may actually produce an opposite effect by introducing a sense of anxiety and fear.

In spite of all these health benefits and the sheer pleasure of the act, Americans may still need a boost. At least one-third of American couples report “inhibited sexual desire,” according to The Masters and Johnson Institute.

Sex therapists say sex acts on the principal of “use it or lose it.” So, for your heart, mind, and soul, the best advice may be to "Just do it."

Susie Michelle Cortright is the author of several books for women and founder of the award-winning Momscape.com, a website designed to help busy women find balance. Visit http://www.momscape.com today and get Susie's *free* course-by-email "6 Days to Less Stress."