Geographic variation in incidence of coronary heart disease in Britain: the contribution of established risk factors

Abstract

Objective: To determine the extent to which geographic variation in the incidence of major coronary heart disease (CHD) in Great Britain may be explained by established risk factors.

Design: Prospective study.

Setting: 24 British towns with widely differing CHD mortality.

Subjects: 7735 men followed up from screening in 1978-80 for 15 years.

Main outcome measures: Percentage of variance between the towns in major CHD incidence that can be explained by individual characteristics of men in the towns.

Results: Age standardised incidence rates over a 15 year period varied from 0.52% per annum in Maidstone to 1.07% per annum in Dewsbury and tended to follow the known pattern of higher rates in Scottish and northern English towns and lower rates in southern English towns ("north-south gradient"). Higher town incidence rates were related to prevalence of current cigarette smoking, low physical activity, and low alcohol consumption, and to mean body mass index, mean systolic blood pressure, low mean height, and prevalence of manual social class, but not to mean serum total cholesterol. The 95% range for true age adjusted CHD incidence (over 15 years) was estimated as 0.58-1.03% per annum among British towns. After adjustment for baseline smoking status, physical activity, body mass index, alcohol consumption, systolic blood pressure, serum total cholesterol, occupational social class, and height, this variation was reduced by 50%. A model based on these eight variables accounted for the major part of the north-south gradient.

Conclusions: Much of the variation in CHD incidence among British towns was accounted for by established risk variables. The remaining unexplained variation may be related to measurement error in the established risk variables, to environmental factors such as climate, or to the combined effect of a wide range of minor risk factors.

Figure 1

Scatter plot of residuals on log (odds) scale when model is fitted against latitude of town (units are minutes, compared with average latitude of 24 towns). Each point represents a town. Residuals are the difference between CHD incidence observed and that expected based on the model. Negative residuals imply that a town's CHD incidence was lower than expected. (A) Only age is fitted in the model. (B) Age, smoking, physical activity, body mass index, alcohol intake, systolic blood pressure, cholesterol, social class, and height are fitted