Trajectories of health-related quality of life differ by age among adults: results from an eight-year longitudinal study.

To date, only a few studies have assessed determinants of health trajectories using longitudinal health survey data. Multilevel models were used to estimate health-related quality of life trajectories and assess factors associated with variations among trajectories, controlling for mortality effects and cohort membership. Four biennial cycles (1996/97-2004/05) of the Canadian National Population Health Survey were used. Information for 13,665 respondents, including those who were subsequently institutionalized and/or died, was used. A typical life-course trajectory was concave with a slow decline until the age of 60, followed by a more rapid decline. Receiving social assistance, lower education and not being married had significant negative impacts on trajectories for young (age 18-39) and middle-aged (40-64). Chronic conditions and health behaviours such as smoking were important for seniors (65+). It is important to focus on the most relevant and important determinants of health in each phase of life.