medwireNews: Smokers who stop by choice, rather than for health reasons, have a lower risk for developing type 2 diabetes later in life, results of a large Chinese study show.
Among 198,574 male participants of the prospective China Kadoorie Biobank, occasional smokers (n=22,435) had a 12% increased risk for developing diabetes compared with never-smokers (n=28,214), after adjustment for potential confounders, during approximately 9 years of follow-up.
The adjusted risk was slightly higher, at 14%, among those who were ever-regular smokers (current smokers and ex-smokers who stopped due to illness; n=134,975), but was not significantly different from never-smokers in participants who had stopped smoking by choice (ex-smokers; n=12,950).
Diabetes incidence was 3.0 cases per 1000 person–years for men and 3.3 cases per 1000 person-years for the 284,015 women included in the study.
The study participants, who were aged 30–79 years at baseline, were recruited from five urban and five rural areas across China between 2004 and 2008, and the researchers found that the hazard ratios for developing diabetes were greater in urban areas than in rural areas.
Zhengming Chen (University of Oxford, UK) and co-authors say that this observation is “consistent with previous findings showing that the tobacco epidemic is still at an early stage in China, particularly in rural areas.”
Among urban men, ever-regular smokers had a significant 18% increased risk for diabetes compared with never smokers, and the risk increased with decreasing age at starting smoking and increasing amount smoked per day.
A similar, albeit more modest, pattern was observed among the rural men.
But importantly, stopping smoking by choice for even the shortest amount of time (<5 years) resulted in no excess diabetes risk compared with never smoking.
By contrast, the risk was a significant 42% higher among individuals who had stopped smoking for health reasons within 5 years of baseline. However, the excess risk in this group fell to nonsignificant levels after 15 years of not smoking whereas it began to rise among the participants who had stopped by choice, which the researchers say could be partly attributable to weight gain following smoking cessation.
Of the women studied, 7811 (3%) had ever smoked regularly. These women had a 33% increased risk for diabetes compared with their non-smoking counterparts and their risk also increased with decreasing age at starting smoking and increasing amount smoked per day.
Writing in The Lancet Public Health, Chen et al say that further studies are needed to determine the causality of the association between smoking status and diabetes.
They conclude: “Irrespective of causality, smoking should be targeted as an important lifestyle factor in disease prevention strategies, including for diabetes, in China and elsewhere.”
By Laura Cowen
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