Abstract
SummaryBackgroundIn developed countries, smoking is associated with increased risk of diabetes. Little is known about the association in China, where cigarette consumption has increased (first in urban, then in rural areas) relatively recently. Moreover, uncertainty remains about the effect of smoking cessation on diabetes in China and elsewhere. We aimed to assess the associations of smoking and smoking cessation with risk of incident diabetes among Chinese adults.MethodsThe prospective China Kadoorie Biobank enrolled 512 891 adults (59% women) aged 30–79 years during 2004–08 from ten diverse areas (five urban and five rural) across China. Participants were interviewed at study assessment clinics, underwent physical measurements, and had a non-fasting blood sample taken. Participants were separated into four categories according to smoking history: never-smokers, ever-regular smokers, ex-smokers, and occasional smokers. Incident diabetes cases were identified through linkage with diabetes surveillance systems, the national health insurance system, and death registries. All analyses were done separately in men and women and Cox regression was used to yield adjusted hazards ratios (HRs) for diabetes associated with smoking.Findings68% (n=134 975) of men ever smoked regularly compared with 3% (n=7811) of women. During 9 years' follow-up, 13 652 new-onset diabetes cases were recorded among 482 589 participants without previous diabetes. Among urban men, smokers had an adjusted HR of 1·18 (95% CI 1·12–1·25) for diabetes. HRs increased with younger age at first smoking regularly (1·12, 1·20, and 1·27 at ≥25 years, 20–24 years, and <20 years, respectively; p for trend=0·00073) and with greater amount smoked (1·11, 1·15, 1·42, and 1·63 for <20, 20–29, 30–39 and ≥40 cigarettes per day; p for trend<0·0001). Among rural men, similar, albeit more modest, associations were seen. Overall, HRs were more extreme at higher levels of adiposity. Among men who stopped by choice, there was no excess risk within 5 years of cessation, contrasting with those who stopped because of illness (0·92 [0·75–1·12] vs 1·42 [1·23–1·63]). Among the few women who ever smoked regularly, the excess risk of diabetes was significant (1·33 [1·20–1·47]).InterpretationAmong Chinese adults, smoking was associated with increased risk of diabetes, with no significant excess risk following voluntary smoking cessation.FundingWellcome Trust, Medical Research Council, British Heart Foundation, Cancer Research UK, Kadoorie Charitable Foundation, Ministry of Science and Technology, National Natural Science Foundation of China, and China Scholarship Council.
Highlights
An estimated 425 million people have diabetes, causing a substantial burden of premature death and disability.[1]
Incident diabetes cases were identified through linkage with diabetes surveillance systems, the national health insurance system, and death registries
Added value of this study Our aim was to assess the associations of smoking and smoking cessation with risk of incident diabetes among urban and rural Chinese adults
Summary
An estimated 425 million people have diabetes, causing a substantial burden of premature death and disability.[1] In China, the prevalence of diabetes has increased dramatically over recent decades, from approximately 1% in 1980,2 to around 11% in 2013.3 the factors underlying this escalating prevalence are incompletely understood. Apart from increasing adiposity,[4] other lifestyle factors, including smoking, might play a part.[5] In China, cigarette consumption has increased markedly over a similar time period, first in urban areas, in rural areas, this increase has occurred almost exclusively in men.[6] About two-thirds of Chinese men smoke,[6] consuming roughly 40% of the world’s cigarettes.[7] A few prospective studies[8,9] have examined the association between smoking and diabetes in China, but these were constrained by small sample size, short follow-up (usually
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