I found this excellent article at Sanctuary for the Abused, describing how being in an abusive relationship can lead to a variety of serious, even life-threatening, illnesses.
Another related article is Chronic Stress Alters our Genetic Immune Response.
This is an extremely serious issue for those who have lived, or are living, in abuse. I cannot emphasize enough how critical this is. All forms of abuse, including verbal abuse, have the power to literally kill.