Adiposity and risk of ischaemic and haemorrhagic stroke in Chinese men and women: a prospective study of 0.5 million adults

Background China has high stroke rates despite the population being relatively lean. Uncertainty persists about the relevance of adiposity to risk of stroke types. Methods The China Kadoorie Biobank enrolled 512,891 adults aged 30-79 years from 10 areas during 2004-08. During 9.2 years of follow-up, 32,448 strokes (~90% image confirmed) were recorded among 489,301 participants without prior cardiovascular disease. Cox regression yielded adjusted hazard ratios (HRs) for ischaemic stroke (IS, n=25,210) and intracerebral haemorrhage (ICH, n=5,380) associated with adiposity. Findings Mean baseline BMI was 23.6 kg/m2 and 68% had BMI <25 kg/m29 . Throughout the range examined (17-32 kg/m2), each 5 kg/m2 higher BMI was associated with 8.3 mmHg higher SBP. BMI was positively associated with IS (1.30, 95%CI 1.28-1.33, per 5 kg/m2 higher), generally consistent with that predicted by equivalent differences in SBP (1.25 [1.24-1.26]). The HR for ICH (1.11 [1.07-1.16] per 5 kg/m2 BMI) was less extreme, and much weaker than that predicted by the corresponding difference in SBP (1.48, 1.46-1.50). Other adiposity measures showed similar associations with stroke types. After adjustment for usual SBP, the positive associations with IS were attenuated (e.g. 1.05 [1.03-1.07] per 5 kg/m2 BMI); for ICH they were reversed (0.73 [0.70- 0.77]). High adiposity (BMI>23 kg/m2 ) accounted for 15% of total stroke (17% IS, 7% ICH). Interpretation In Chinese adults, adiposity was strongly positively associated with IS, chiefly 19 through its effect on blood pressure. For ICH, leanness, either per se or through some other 20 factor(s), may increase risk, offsetting the protective effects of lower blood pressure.