They also had higher risks of clogged arteries, heart failure, and reduced blood flow to the limbs.
The risks were lower for diabetics who quit smoking, but still moderately higher than risks among never smokers, the researchers write in the journal Circulation.
Lead author An Pan told Reuters Health by email that smoking is still common among people with diabetes, despite efforts to discourage it.
"We wanted to know whether smoking was related to total mortality and cardiovascular events among diabetic patients, and whether smoking cessation would reduce the risks," said Pan, who is a professor at Huazhong University of Science and Technology in China.
According to the Centers for Disease Control and Prevention, smoking can worsen the health risks that go along with diabetes, such as heart and kidney disease, nerve damage, and blindness.
Pan's team pooled the data from 89 earlier studies of smoking among adults with type 2 diabetes and found that diabetic smokers were around 1.5 times more likely to experience clogged arteries, stroke, overall heart disease, and heart failure.
In addition, smokers were more than twice as likely to suffer from peripheral artery disease, or reduced blood flow to the limbs, than patents who did not smoke.
Former smokers had 1.2 times the risk of clogged arteries and 1.1 times the risk of overall heart disease, compared to never-smokers.
Using the risk estimates from their review and global rates of deaths from diabetes, the researchers estimated that smoking accounted for 14.6 percent of deaths in diabetic men and 3.3 percent of deaths in diabetic women worldwide.
Dr. Wael Al-Delaimy, division chief of global health at the University of California, San Diego, said part of the problem may be the care diabetes patients receive.
"The physician caring for the diabetes patient might be focusing on cardiovascular risk factors or diabetes complications and diet and weight control while neglecting smoking as another important risk factor," Al-Delaimy told Reuters by email.
Pan said some smokers may be reluctant to quit due to concerns about gaining weight in the short term. However, he noted, "The long-term benefits clearly overweigh the short-term side effects."
Pan advises diabetic patients who are smokers "to seek professional help to quit smoking."
Al-Delaimy agreed, saying, "If you are a patient suffering from diabetes and smoking cigarettes, or if you know a family member, friend or anyone else who is diabetic and smoking, there is still opportunity to substantially decrease further complications and suffering or even early death by quitting smoking."
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