Purpose: The K6 is a 6-item scale of nonspecific psychological distress included in many nationally representative health surveys. This study examines whether persons with serious psychological distress (SPD), as measured by the K6, have a greater risk of mortality than persons without SPD and whether K6 scores have a dose-response relationship with mortality.
Methods: The data used are the combined 1997-2000 National Health Interview Surveys linked with the National Death Index through 2002. We examined the relationship between K6 score and mortality using a cut-off of 13 for SPD and then a 5-level categorical variable. Cox proportional hazards models were adjusted for potential confounders, including sociodemographic factors, health behaviors, and physical illness.
Results: The age- and sex-adjusted mortality hazard ratio associated with SPD was 2.2 (1.9, 2.5). After adjusting for covariates, SPD remained related to increased mortality, hazard ratio, 1.30 (1.13, 1.49). Adjusted mortality hazard ratios for the categorical variable demonstrated a dose-response effect with hazard ratios of 1.00, 1.10, 1.22, 1.51, and 1.54. All 4 exposure categories were statistically significantly different from the reference group.
Conclusions: SPD as measured by the K6 is associated with increased mortality, even after adjusting for potential confounders; scores were related to increased mortality in a dose-response fashion.