This review study suggests that the effect from loneliness and social isolation on mortality is equivalent to obesity, and that past studies put it into the same category as being an alcoholic, or smoking 15 cigarettes a day. Bottom line: Friendships and having a social network are important to health! Note that the study also found: "...loneliness and social isolation better predict premature death among populations younger than 65 years." From Medical Xpress:
Ask people what it takes to live a long life, and they'll say things like exercise, take Omega-3s, and see your doctor regularly. Now research from Brigham Young University shows that loneliness and social isolation are just as much a threat to longevity as obesity. Loneliness and social isolation can look very different. For example, someone may be surrounded by many people but still feel alone. Other people may isolate themselves because they prefer to be alone. The effect on longevity, however, is much the same for those two scenarios.
The association between loneliness and risk for mortality among young populations is actually greater than among older populations. Although older people are more likely to be lonely and face a higher mortality risk, loneliness and social isolation better predict premature death among populations younger than 65 years.
The study analyzed data from a variety of health studies. Altogether, the sample included more than 3 million participants from studies that included data for loneliness, social isolation, and living alone. Controlling for variables such as socioeconomic status, age, gender, and pre-existing health conditions, they found that the effect goes both ways. The lack of social connections presents an added risk, and the existence of relationships provides a positive health effect.
Previous research from Holt-Lunstad and Smith puts the heightened risk of mortality from loneliness in the same category as smoking 15 cigarettes a day and being an alcoholic. This current study suggests that not only is the risk for mortality in the same category as these well-known risk factors, it also surpasses health risks associated with obesity.