The burden of depression on mortality over six decades

Major depression afflicts about 5% of the Canadian population in any year, and costs the Canadian economy more than $14 billion each year. It degrades social functioning and physical health significantly, and its most severe consequences include early death. Because prior studies on depression and mortality were based on fairly short follow-up times, the existing evidence derives from depression's short-term effects. The current application proposes to investigate the association between depression and death with a long focus: six decades. We will do so in one of the longest running studies of psychiatric disorders - the Stirling County Study - that dates back to the early 1950s and consists of three successive samples (1952, 1970, and 1992) involving 4,140 subjects. We propose to link these survey responses to Statistics Canada data up to 2011, thereby providing 59 years of follow-up data on mortality for the 1952 sample, 41 years of follow-up data on the 1970 sample, and 19 years of follow-up data on the 1992 sample. The proposed research has three specific aims. The first aim is to investigate premature death associated with depression in the three Stirling County Study Samples, and to determine whether mortality rates differ by gender and socioeconomic status. The second aim is to determine which types of depression are most strongly associated with mortality, by investigating clinically identified sub-types of depression thought to be most severe, and scientifically identified sub-types based on results of statistical analyses of depressive symptoms recorded among participants in 1992. The third aim is to investigate the role of other risk factors for disease in the association between depression and mortality, focusing on alcoholism, obesity, cigarette smoking, and heart problems. The successful completion of these aims will yield new insights into the consequences of depressive illness and will contribute to reducing the public health burden of depression.