If you haven't seen it, take a look at Is Marriage Good for Your Health? by Tara Parker-Pope in the New York Times Magazine (April 18, 2010). Among other things, it's a clarification of the frequently expressed thought that marriage (it's in just about all our interpersonal communication textbooks)--and long-term relationships generally--are good for your health. Well, it appears that only good relationships are good for your health and bad relationships are bad for your health--tho' I wonder why we needed tons of studies to prove that. More interesting are the health problems that marital discord can create or make worse. Among those mentioned are elevated stress hormones and increased risks of diabetes, heart disease, mood swings, and depression. Also, wounds take longer to heal, the immune system is weakened, and an outbreak of herpes seems more likely under conditions of marital discord.
All in all, a good reason to study interpersonal communication and conflict management.
Along with this article, take a look at Bella DePaulo's discussion for Psychology Today: http://www.psychologytoday.com/blog/living-single/201004/is-good-marriage-good-your-health