The review included 25 studies of smoking and diabetes among a million people ages 16 and older in the U.S., U.K., Europe, Japan, and Israel.
None of those people had type 2 diabetes when the studies started. But more than 45,000 participants developed type 2 diabetes during the studies, which lasted for five to 30 years.
The reviewers analyzed all the data and concluded that the chance of developing type 2 diabetes was 44% higher for smokers than for nonsmokers.
Heavy smokers -- people who smoke at least 20 cigarettes per day -- were more likely to develop type 2 diabetes than people who smoke fewer cigarettes or ex-smokers.
The pattern varied somewhat in its intensity but held for all but one of the reviewed studies. Still, the studies don't prove that smoking causes type 2 diabetes.
The reviewers considered some diabetes risk factors, including the fact that type 2 diabetes becomes more common with age.
But the review doesn't show whether exercise, social class, or education affected the results.
The reviewers -- who included Carole WIlli, MD, of Switzerland's University of Lausanne -- report their findings in tomorrow's edition of The Journal of the American Medical Association.
The review may be a "conservative underestimate of the true association
between smoking and type 2 diabetes," states an editorial published with the study.
Eric Ding, ScD, and Frank Hu, MD, PhD, wrote the editorial. They work at Harvard School of Public Health, Harvard Medical School, and Boston's Brigham and Women's Hospital.
By Miranda Hitti
Reviewed by Louise Chang
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