The death of an individual in early and middle adulthood is an untimely event whose tragic effects are experienced by the parents, siblings, partners, children ^{Footnote 1 , Footnote 2 , Footnote 3} and friends of the deceased individual. Preventing premature death is a foremost goal of health care and public health programs, and of society at large.

Premature mortality is a measure of unfulfilled life expectancy. While conventional definitions of premature mortality and Years of Potential Life Lost ^{Footnote 4} include all people from birth to age 65 ^{Footnote 5} or 75 ^{Footnote 6} years, such designations obscure our understanding of factors preventable in adulthood. For example, deaths in childhood largely occur in infancy—due to birth defects and preterm birth. At the other end of the lifespan, by including seniors aged 65 to 75 years—who account for the greatest number of deaths—the cause of death is skewed toward cancer and cardiovascular disease. Among Canadians of all ages, the top five causes of death are cancer (30%), heart disease (21%), stroke (6%), lung disease (5%) and unintentional injury (4%). ^{Footnote 7} However, upon restricting to Canadians aged 25 to 34 years, the top five leading causes of death shift to unintentional injury (29%), suicide (20%), cancer (12%), heart disease (5%) and homicide (5%). ^{Footnote 7} For those aged 35 to 44 years, the top five leading causes of death include unintentional injury, suicide and liver disease, the latter often due to alcohol overuse and injection drug use. In Toronto, the causes of premature death follow the same pattern