ABSTRACT
Objective To assess the relationship between body mass index (BMI) and ischaemic heart disease (IHD) mortality,especially in populations with low mean BMI levels.Methods We examined the data from a population-based,prospective cohort study of 220 000 Chinese men aged 40-79,who were enrolled in 1990-1991,and followed up ever since to 1/1/2006.Relative risks of the deaths from IHD by the baseline BMI were calculated,after controlling age,smoking,and the other potential confounding factors.Results The mean baseline BMI was 21.7 kg/m~2,and 2763 IHD deaths were recorded during the 15-year follow-up (6.8% of all deaths) program.Among men without prior vascular diseases at baseline,there was a J-shaped association between BMI and IHD mortality.When baseline BMI was above 20 kg/m~2,there was a strongly positive association of BMI with IHD risk,with each 5 kg/m~2 higher in BMI associated with 21%(95%CI:9%-35%,P=0.0004) higher IHD mortality.Below this BMI range,the association appeared to be reverse,with the risk ratios as 1.00,1.11,and 1.14,respectively,for men with BMI 20-21.9,18-19.9,and ＜ 18 kg/m~2.The excess IHD risk observed at low BMI levels persisted after restricting analysis to never smokers or excluding the first 3 years of follow-up.Conclusion Lower BMI was associated with lower IHD risk among people in the so-called 'normal range' of BMI values (20-25 kg/m~2).However,below that range,the association might well be reversed.