Your curiosity is well founded - this is complete nonsense. In fact both masturbation and partnered sex are very good for your general health, provided you practise safe sex in the latter case of course. This is from Wikipedia:

"A 1997 study in the British Medical Journal based upon 918 men age 45-59 found that after a ten year follow-up, men who had fewer orgasms were twice as likely to die of any cause as those having two or more orgasms a week."

You can see how this makes sense - when you masturbate your heart beats faster, and your breathing speeds up. Since the heart and lungs are two of the most important organs in the body, any safe activity that exercises them is good for your general health.

Other studies have found that frequent masturbation reduces the risk of prostate cancer - a doctor who studied the evidence recommended that teenagers masturbate at least six times a week.

Keep thinking scientificually, and don't accept nonsense!