A new report confirms that smokers and those exposed to secondhand smoke have an increased risk for developing type 2 diabetes.
Researchers from the Harvard T.H. Chan School of Public Health, Huazhong University of Science and Technology in China, and the National University of Singapore published the report in The Lancet Diabetes & Endocrinology.
They conducted a meta-analysis of 88 previous studies on the link between smoking and type 2 diabetes risk, examining data from almost 6 million study participants.
“It is well established that secondhand smoke is implicated in many tobacco-caused diseases, but the link between exposure to someone else’s smoke and increased diabetes risk is new,” said Dr. Michael Steinberg, director of the Rutgers Tobacco Dependence Program at Robert Wood Johnson Medical School.
The researchers say that 11 percent of type 2 diabetes cases in men and 2.4 percent in women (more than 27 million cases worldwide) may be attributed to active smoking.
Compared with people who never lit up, current smoking boosted the risk of type 2 diabetes by 37 percent.
In former smokers, it increased the risk by 14 percent.
In those exposed to secondhand smoke, it raised the risk for type 2 diabetes by 22 percent.
The More You Smoke, the More You’re at Risk
The analysis also revealed that the more you smoke, the higher your risk will be.
Light smokers had a 21 percent higher risk while moderate smokers had a 34 percent higher risk, and heavy smokers had a 57 percent risk for developing type 2 diabetes.
“Despite the global efforts to combat the tobacco epidemic, cigarette use remains the leading cause of mortality and morbidity worldwide,” said An Pan, the first author of the study and professor of epidemiology at the School of Public Health at the Tongji Medical College at China’s Huazhong University of Science and Technology, in a press release.
Pan said it also stresses the need to make public places free from smoke.
There is good news for quitters, though.
The researchers say the risk for type 2 diabetes went down over time after smokers kicked the habit.
There was a 54 percent increased risk of type 2 diabetes in people who quit smoking within the past five years. That went down to 18 percent after five years and decreased to 11 percent after a decade.
Earlier this year, the same journal published a report that found diabetes patients who quit smoking may see a temporary impairment in glycemic control that may last for up to three years.
Building a Case to Tie Smoking, Diabetes
Smoking is already associated as a risk factor for cancer, respiratory disease, and heart disease, but it hasn’t been as easy to build the case to link it with type 2 diabetes.
In 2014, the U.S. Surgeon General's report contained a section on smoking and diabetes risk and mentioned the causal relation between them. That report did not touch on the link between passive smoking and smoking cessation with diabetes risk.
“The current study goes a step further and suggests that secondhand smoke may also increase the risk of diabetes,” Steinberg told Healthline.
Steinberg said the findings reinforce the importance of tobacco control policies.
Though it’s not clear how smoking causes diabetes, Steinberg said that further research will be vital to improving public health. Tobacco and diabetes are two of the leading risk factors for cardiovascular disease, he added.
Dr. Frank Hu, professor of nutrition and epidemiology and coauthor of the report, told Healthline how smoking can be a pathway for diabetes development.
Smokers tend to be leaner than nonsmokers, but they also have increased abdominal obesity and visceral fat. That is a critical risk factor for insulin resistance and diabetes.
Smoking is tied to increased chronic inflammation, another underlying risk factor for insulin resistance and diabetes.
In addition, toxic chemicals can damage human beta cells, leading to their dysfunction and impaired insulin secretion.
“Cigarette smoking should be considered as a key modifiable risk factor for diabetes. Public health efforts to reduce smoking will have a substantial impact on the global burden of type 2 diabetes,” Hu said in a statement.