In a very famous epidemiology study, one of the most referenced of its kind because of its impressive sample size, UC Berkeley researchers Dr. Lisa Berkman and Dr. Leonard Syme studied seven thousand residents of Alameda County, California. All of them were observed for a nine-year period in order to discover all the common denominators among the healthiest residents. The researchers controlled for gender, race, ethnicity, socioeconomic status, alcohol, tobacco, obesity, depression, and medical care. The study showed conclusively that the healthiest people were the ones with the greatest quantity and quality of social support. And conversely, the most socially isolated people had the greatest morbidity (rate of disease) and mortality. A large social support network and high frequency of contact directly correlated with health and made all the difference between health and illness.
In an eight-year follow-up by Berkman and Syme of the Alameda County study with 6,848 of the initial seven thousand participants, the researchers found results consistent with the first study: a very strong correlation between the amount and quality of social support and reduced morbidity and mortality of all causes. Those who lived fairly isolated lives had a mortality rate that was three times greater than that of those who had family or friends. It also found a very robust inverse correlation between the quantity and quality of social support and cancer. Those who were most socially isolated had a significantly greater chance of developing cancer and dying from it.
Berkman, L., and Syme, S. Social networks, host resistance, and mortality: a nine-year follow-up study of Alameda County residents. American Journal of Epidemiology 1982;109(2):186-204.