Loneliness and social isolation increase cancer incidence in a cohort of Finnish middle-aged men. A longitudinal study.

Globally, cancer is the second leading cause of death. Loneliness has been suggested as a risk factor for cancer mortality. However, connections between loneliness, social isolation, and cancer are poorly understood. In our longitudinal study (mean follow-up: 20.44 years) of 2570 middle-aged men, loneliness, social isolation, and health-related factors were measured at baseline. Cox proportional hazards analysis was used to examine the association between cancer incidence, loneliness, and social isolation. The effect of relationship status on cancer mortality among cancer patients was tested with the Kaplan-Meier method. Loneliness was associated with total cancer incidence after adjustments for tested lifestyle and health-related covariates. Social Isolation was associated with total cancer incidence, except when adjusted for lifestyle, diet, or Human Population Laboratory (HPL) Depression Scale scores. Loneliness was associated with lung cancer incidence, except when adjusted for HPL Depression Scale scores. There was no significant association between social isolation and lung cancer. Neither loneliness nor social isolation were connected with prostate or colorectal cancer. Being single at baseline was associated with worse survival outcomes for cancer patients. Our findings suggest that regardless of the social network size, loneliness among middle-aged men is associated with an increased likelihood of cancer.