The Multiple Sclerosis Quarterly Report has an article on caregiver stress and what it does to the caregiver's body. This study is about caregivers of those with MS, however the statistics mirror nearly every study on caregiver stress I have read.
The study begins with that idea in mind:
"Caregiving Stress in General
The role of caring for a physically-challenged loved one can be both rewarding, as well as a physically and emotionally hard experience. Multiple studies have reported that chronic caregiving stress increases morbidity and mortality for the CarePartner. The National Alliance for CareGiving estimates that caregiving spouses between the ages of 66 and 96 years who are experiencing mental or emotional strain have a 63% higher risk of dying than people the same age who are not caregivers. Additional research shows that stress from chronic caregiving negatively impacts the cardiovascular, immune, and endocrine functions. Caregivers have increased numbers of respiratory tract infections, a poorer response to influenza virus, and slower wound healing than wellmatched noncaregivers."