Did it fall or was it pushed? The contribution of trends in established risk factors to the decline in premature coronary heart disease mortality in New Zealand

Abstract

Objective: To estimate the contribution of trends in three risk factors -systolic blood pressure (SBP), total blood cholesterol (TBC) and cigarette smoking -to the decline in premature coronary heart disease (CHD) mortality in New Zealand from 1980-2004. Method: Risk factor prevalence data by 10-year age group (35-64 years) and sex was sourced from six national or Auckland regional health surveys and three population censuses (the latter only for smoking). The data were smoothed using two-point moving averages, then further smoothed by fitting quadratic regression equations (SBP and TBC) or splines (smoking). Risk factor/CHD mortality hazard ratios estimated by expert working groups for the World Health Organization Global Burden of Disease Study 2001 were used to translate average annual changes in risk factor prevalences to the corresponding percentage changes in premature CHD mortality. The expected trends in CHD mortality were then compared with the observed trend to estimate the contribution of each risk factor to the decline. Findings: Approximately 80% (73% for males, 87% for females) of the decline in premature CHD mortality from 1980 to 2004 is estimated to have resulted from the joint trends in population SBP and TBC distributions and smoking prevalence. Overall, approximately 42%, 36% and 22% of the joint risk factor effect was contributed by trends in SBP, TBC and smoking respectively. Conclusion: Our estimate for the joint risk factor contribution to the CHD mortality decline of 80% exceeds those of two earlier New Zealand studies, but agrees closely with a similar Australian study. This provides an indicator of the scope that still remains for further reduction in CHD mortality through primary and secondary prevention.

Proportion of the Decline in Cardiovascular Mortality Disease due to Prevention Versus Treatment: Public Health Versus Clinical Care

“…Capewell, Beaglehole, and colleagues (17) applied the IMPACT model to data from New Zealand for the period from 1982 to 1993 and estimated that treatments accounted for ∼46% of the decline in CHD mortality and that changes in risk factors accounted for ∼54% (smoking 30%, cholesterol 12%, and blood pressure 8%). Using a different methodology, Tobias and colleagues suggested that ∼80% of the decline in CHD mortality from 1980 to 2004 could be explained by secular changes in smoking, SBP, and total cholesterol, attributing most of the effect of blood pressure and total cholesterol to improvements in lifestyle, particularly diet, because rates of use of antihypertensive medications and cholesterollowering medications were low into the 1990s (117).…”

The decline in coronary heart disease mortality is slowing in young adults (Australia 1976–2006): A time trend analysis

“…A growing body of evidence suggests that 45%-70% of the recent decline in CHD mortality could be attributed to decrease in risk factors [2,4,6,18,19]. Furthermore Taylor et al, in Australia and New Zealand, using a different methodology, estimated that the decline in risk factors could explain 74% of the decline in CHD mortality in men, and 84% in women [7,8,20].…”

“…In Australia and New Zealand, even more of the decline, around 80% has been attributable to changes in risk factors [7,8].…”

Response to: Tobias et al. on the decline of CHD mortality in New Zealand

“…In their paper, Tobias et al 1 state that dietary trends are less comprehensive and reliable than data on other risk factors but they recognise the possible importance of diet in the decline in CHD mortality in New Zealand. We would like to submit further data on diet in relation to the fall in CHD mortality in Australia and the US.…”