Levels of anxiety and depression as predictors of mortality: the HUNT study

BACKGROUND: Depression is reported to be associated with increased mortality, although underlying mechanisms are uncertain. Associations between anxiety and mortality are also uncertain. AIMS: To investigate associations between individual and combined anxiety/depression symptom loads (using the Hospital Anxiety and Depression Scale (HADS)) and mortality over a 3-6 year period. METHOD: We utilised a unique link between a large population survey (HUNT-2, n = 61 349) and a comprehensive mortality database. RESULTS: Case-level depression was associated with increased mortality (hazard ratio (HR) = 1.52, 95% CI 1.35-1.72) comparable with that of smoking (HR = 1.59, 95% CI 1.44-1.75), and which was only partly explained by somatic symptoms/conditions. Anxiety comorbid with depression lowered mortality compared with depression alone (anxiety depression interaction P = 0.017). The association between anxiety symptom load and mortality was U-shaped. CONCLUSIONS: Depression as a risk factor for mortality was comparable in strength to smoking. Comorbid anxiety reduced mortality compared with depression alone. The relationship between anxiety symptoms and mortality was more complex with a U-shape and highest mortality in those with the lowest anxiety symptom loads.