Background: This report concerns long-term mortality risks associated with depression, and the potentially confounding factors of alcoholism and cigarette smoking, as experienced by a general population assessed at a baseline in 1952, followed for re-assessment of survivors in 1968, and for death by 1992.
Methods: Self-report and physician-report information was gathered in 1952 and again in 1968 about a sample of 1,079 adults. At the end of follow-up in 1992, the vital status of all subjects was known. Comorbidity among depression, alcoholism, and smoking was investigated. Cox regression models were employed to estimate hazard ratios (HRs) as indicators of mortality risk. Models including age, gender, and depression were fit for the complete sample at baseline as well as for re-assessed survivors. Models simultaneously controlling for the mortality risks associated with depression, alcoholism, and heavy smoking were fit for men.
Results: At the baseline in 1952, depression was somewhat more common among women than men (4% compared to 6%) but was found to carry a significant mortality risk only among men (HR 2.7, 95% CI 1.6-4.7). Based on re-assessments made in 1968, depression was associated with mortality risk among both men (HR 2.2, 95% CI 1.0-4.5) and women (HR 2.1, 95% CI 1.2-3.8). In 1952, more than 20% of men smoked cigarettes excessively and 8% abused alcohol, but very few of these groups of men were also depressed. In the original sample and also among the survivors, depression, alcoholism, and heavy smoking were separately associated with mortality among men. Depression and alcoholism carried a more immediate mortality risk while heavy smoking a more delayed one.
Conclusions: At the baseline of the Stirling County Study, the mortality risk associated with depression among men was not enhanced or explained by abuse of alcohol or nicotine, mainly because comorbidity was rare at that time. The longitudinal research of the study has pointed to a number of psychiatrically-relevant time-trends such as the fact that an association between depression and cigarette smoking did not appear until the 1990s. It is hypothesized that a similar trend may emerge over time regarding the comorbidity of depression and alcoholism. A trend reported here was that, while depressed women in the original sample did not carry a significant mortality risk, the surviving women who were depressed at the time of re-assessment exhibited a mortality risk that was as significant as that for men. Such information may provide a useful back-drop for future investigations.