Some links:

http://www.aolhealth.com/conditions/ejaculation-frequency-and-prostate-cancer

http://www.time.com/time/magazine/article/0,9171,993150,00.html

Here's a quote from the 2nd link:

Studies are showing that arousal and an active sex life may lead to a longer life, better heart health, an improved ability to ward off pain, a more robust immune system and even protection against certain cancers, not to mention lower rates of depression.