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Smoking linked to higher risk for type 2 diabetes
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Adults who smoke cigarettes, as well as adults exposed to secondhand smoke, may increase their risk for developing type 2 diabetes vs. those who are not exposed to tobacco smoke, according to research in The Lancet Diabetes & Endocrinology.
In a meta-analysis of prospective studies involving nearly 6 million participants, researchers investigating the link between smoking behaviors and diabetes risk found that 11.7% of type 2 diabetes cases in men and 2.4% in women may be attributable to active smoking, and that the risk decreases once smokers quit.
“Cigarette smoking should be considered as a key modifiable risk factor for diabetes,” Frank Hu, MD, professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health, said in a press release. “Public health efforts to reduce smoking will have a substantial impact on the global burden of type 2 diabetes.”
Hu and An Pan, PhD, professor of epidemiology at the School of Public Health, Tongji Medical College, Huazhong University of Science and Technology in Wuhan, Hubei, China, and colleagues analyzed data from 88 prospective studies that reported the risk for type 2 diabetes by baseline smoking status, with 5,898,795 participants and 295,446 incident cases of type 2 diabetes. Researchers used calculated pooled RRs to analyze the link between smoking status and risk for type 2 diabetes.
Researchers found that participants who identified as current smokers had a pooled RR of 1.37 (95% CI, 1.33-1.42) vs. nonsmokers; former smokers had a pooled RR of 1.14 (95% CI, 1.1-1.18) vs. nonsmokers; nonsmokers exposed to secondhand smoke had a pooled RR of 1.22 (95% CI, 1.1-1.35).
Researchers also found a dose-response relation for smoking and diabetes risk. Compared with participants who never smoked, those who identified as light smokers had an RR of 1.21 (95% CI, 1.1-1.33), moderate smokers had an RR of 1.34 (95% CI, 1.27-1.41) and heavy smokers had an RR of 1.57 (95% CI, 1.47-1.66).
The risk for diabetes fell as participants quit for longer periods of time. Pooling 10 studies with 1,086,608 participants, researchers found that “new quitters” (within the last 5 years) had an RR of 1.54 (95% CI, 1.36-1.74); middle-term quitters (nonsmokers for 5 to 9 years) had an RR of 1.18 (95% CI, 1.07-1.29) and long-term quitters (at least 10 years) had an RR of 1.11 (95% CI, 1.02-1.2).
“Despite the global efforts to combat the tobacco epidemic, cigarette use remains the leading cause of mortality and morbidity worldwide,” Pan said in a press release. “This study underscores the importance of implementing and enforcing the provisions of the WHO Framework Convention on Tobacco Control. The smoke-free policies can provide protections for nonsmokers and may lead to increased successful cessation in smokers.” – by Regina Schaffer
Disclosure: The researchers report no relevant financial disclosures.
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Deborah Lycett, PhD, PGCHE, FHEA, MBDA, RD, BSc
Pan and colleagues have conducted an important review that is much needed, particularly with the evidence mounting regarding the impact of smoking cessation on diabetes risk and glycemic control. Methodologically, this was an excellent study with comprehensive search terms, the inclusion of only high quality prospective studies, thorough statistical analysis and consideration of publication bias; I feel confident in the study’s findings. However, I am disappointed with the way the 54% increased risk for developing type 2 diabetes, within the first 5 years of quitting smoking, was presented and interpreted. This increased risk is on par with those who had the highest increase in risk (57%) and smoked the greatest number of cigarettes a day. I felt the impact and significance of this finding, which is perhaps the most controversial one in the study, was not made clear and could be easily missed. While this increased risk is temporary, and I would not want to detract from the positive health message that the long-term benefits of smoking cessation are undeniable, the first 5 years of quitting present an important window whereby targeted diabetes prevention may be extremely important. This point and many others are addressed in a well-written discussion, but I fear that readers may have to look a little too hard to find them. I would have liked to have seen the 10% increased risk for developing diabetes during the first 5 years of quitting compared with continuing to smoke made clearer, so that appropriate support can be provided to patients during this time.
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