Looking Upstream
Causes of death cross-classified by risk and condition New Zealand 1997
Public Health Intelligence Occasional Bulletin Number 20
ISBN 0-478-28201-X (Book)
ISBN 0-478-25772-4 (Internet)
HP 3783
Date of publication: March 2004
Date of Revision: November 2004
Causes of death are routinely classified at the level of health conditions (diseases or injuries) using the World Health Organization’s International Classification of Diseases. This is useful for planning health care services, yet for disease prevention or health promotion a classification of causes of death at risk factor level would be more useful.
The author has classified deaths occurring in New Zealand in 1997 by 20 prevalent risk factors using a combination of categorical attribution (rule-based) and counterfactual modelling (population-attributable risk-based) approaches. The result is the first comprehensive listing of causes of death by risk factor for New Zealand.
Approximately 30% of deaths were attributed to the joint effect of dietary factors, including 6% to inadequate vegetable and fruit consumption. Tobacco consumption was responsible for 18% of all deaths (combining active and passive smoking) and insufficient physical activity for almost 10%. Less important behavioural risk factors included alcohol consumption (3% of all deaths), illicit drug use (0.5%) and unsafe sex (0.5%).
Among biological risk factors, higher than optimal total blood cholesterol accounted for 17% of deaths, a larger proportion than in other ‘Western’ societies – probably reflecting New Zealanders’ high consumption of saturated fats (ie, meat and dairy products). This burden surpasses that of higher than optimal systolic blood pressure (13% of deaths) and body mass index (11.5%), although the latter is continuing to rise. All three of these major biological risk factors overlap in large part with the ‘lifestyle’ behaviours contributing to the nation’s dietary and physical activity patterns.
These proximal biobehavioural risk exposures are in turn shaped by more distal sociocultural determinants of health. It was possible to quantify the deaths attributable to relative deprivation (17% of all deaths, an impact equivalent to those of smoking or cholesterol), but not those attributable to discrimination. Unanticipated adverse events related to health care in public hospitals were involved in an estimated 6% of deaths, but in many cases the contribution of the adverse event may have been minor.
Among environmental exposures, microbes accounted for 6.5% of all deaths, air pollution for 3.5% and occupational diseases and injuries for 0.5% – although the latter excludes exposure to psychosocial hazards (job strain) at work.
Among injury hazards, risk factors related to road traffic were responsible for 2% of all deaths, while violence accounted for 2.5% of deaths – mostly through suicide.
Causation is always complex and multifactorial, and cross-classification of causes of death by risk and condition involves a number of simplifying assumptions. Nevertheless, this approach may provide deeper insight into the causal structure of the population’s mortality schedule and so prove useful as a planning tool (especially for disease prevention and health promotion).
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