North-south gradients in Britain for stroke and CHD: are they explained by the same factors?
Morris RW., Whincup PH., Emberson JR., Lampe FC., Walker M., Shaper AG.
BACKGROUND AND PURPOSE: The geographic variation in CHD and stroke within Great Britain is well known. We aimed to quantify these variations and to determine the contribution of established risk factors. METHODS: This prospective study consisted of 7735 men 40 to 59 years of age in 24 British towns who were followed up for 20 years from screening in 1978 to 1980. We compared age-adjusted incidences of major stroke and CHD events in southern England and the rest of Britain before and after adjustment for established cardiovascular risk factors. RESULTS: At least 1 episode of stroke occurred in 467 men (3.54 per 1000 person-years, age standardized) and of CHD in 1299 men (10.05 per 1000 person-years). Event rates varied between towns, from 2.00 to 5.45 per 1000 person-years for stroke and from 6.16 to 12.21 per 1000 person-years for CHD. Incidence for both diseases was highest in Scottish towns and lowest in southern English towns ("north-south gradient"). The hazard ratio for stroke in the rest of Britain compared with southern England was 1.44 (95% confidence interval [CI], 1.16 to 1.78); for CHD, it was 1.32 (95% CI, 1.14 to 1.53). After adjustment for baseline systolic blood pressure, smoking status, physical activity, social class, and height, the hazard ratio was 1.24 (95% CI, 1.00 to 1.54) for stroke and 1.17 (95% CI, 1.02 to 1.35) for CHD. CONCLUSIONS: Similar north-south gradients were observed for major stroke and major CHD events. The magnitude of these gradients was considerably diminished when individual risk variables were taken into account.