Lung function and risk of fatal and non-fatal stroke. The Copenhagen City Heart Study

BACKGROUND: Reduced lung function has been shown to be a significant predictor of non-fatal ischaemic heart disease, and of mortality due to cardiovascular disease. Fewer studies have analysed the relationship between lung function and risk of fatal or non-fatal stroke. The present study presents results on the relation between forced expiratory volume in one second (FEV1) and risk of incident and fatal first-ever stroke. SUBJECTS AND METHODS: The analyses are based on prospective cohort data from 12 878 eligible men and women aged 45-84 years, who participated in the first health examination of the Copenhagen City Heart Study in 1976-1978. The subjects were followed from day of entry until 31 December 1993. During that period 808 first-ever strokes occurred of which 153 were fatal within 28 days. Risk of incident and fatal stroke was estimated by means of Cox hazard regression. The analyses included adjustment for potential confounders: sex, age, smoking, inhalation, body mass index, systolic blood pressure, triglycerides, physical activity in leisure time, education, diabetes mellitus, and antihypertensive treatment. RESULTS: We found an inverse association between FEV1 and risk of first-time stroke. For each 10% decrease in FEV1 in percentage of expected, the relative risk (RR) increased 1.05 (95% CI : 1.00-1.09, P = 0.03). This represents an approximately 30% higher risk of stroke in the group of people with the lowest lung function as compared to the group with the highest lung function. The association between lung function and risk of fatal stroke resembled that of risk of incident stroke (fatal and non-fatal). The RR was 1.11 (95% CI : 1.03-1.19) for each 10% decrease in FEV1 in percentage of expected. This represents approximately a doubling of the risk between the highest and lowest lung function groups. CONCLUSIONS: This study shows that reduced lung function measured in percentage of predicted FEV1 is a predictor of first-time stroke and fatal stroke independent of smoking and inhalation. The high risk of fatal first-ever stroke in the group of people with low lung function may be of significance in both the design and interpretation of clinical trials.