Adding to the list of potential health consequences of smoking, a large study finds that smokers may have a heightened risk of developing type 2 diabetes.
The findings, based on the medical records of more than 1.2 million Korean adults, do not prove that smoking itself causes diabetes. But they may offer yet more incentive for people to avoid smoking or to kick the habit as former smokers generally showed a lower risk than current ones.
Using a national health insurance data, researchers found that initially diabetes-free smokers were more likely than non-smokers to develop the disease - which affects 24 million people in the US, according to a recent study over the next 14 years.
Among men, the odds of being diagnosed with diabetes generally increased in tandem with the intensity of their smoking. Compared with their counterparts who had never smoked, men who lit up at least 20 times a day were 55% more likely to have outpatient visits for diabetes in their medical records by the end of the study period.
Women are light smokers
Among women, that level of smoking, as well as light smoking (one to nine cigarettes per day) were linked to a one-third higher diabetes risk versus never-smokers. This was with a number of factors in diabetes risk including age, weight and self-reported exercise levels taken into account.
Researchers led by Dr Sun Ha Jee, of Yonsei University in Seoul, report the findings in the journal Diabetes Care.
The results are in line with those of some past studies, including one published earlier this year that involved nearly 11,000 middle-aged US adults.
In that study, the one-third of tobacco users who smoked most heavily the equivalent of at least a pack per day for 30 years were 42% more likely to be diagnosed with diabetes than people who had never smoked.
Smoking may promote type 2 diabetes
It's thought that smoking may promote type 2 diabetes the most common form of the disorder, usually diagnosed in adults by causing chronic inflammation throughout the body. Inflammation may, for instance, make body tissues more resistant to the blood-sugar-regulating hormone insulin, and over time such resistance often leads to type 2 diabetes.
The current study is based on medical records for more than 1.2 million diabetes-free Korean adults age 30 and up who underwent periodic medical evaluations for up to 14 years. At the outset, 59% of men were current smokers and 21% were former smokers. Among women, only 4% were current smokers and 2% had quit.
Over that time period, 89,422 individuals or about 7% of the total had at least three outpatient visits for diabetes; about 11,400 were hospitalised for diabetes.
Among male smokers, the risk of having outpatient visits was 30% to 55% higher than that of never-smokers, depending on how many cigarettes they smoked per day; the odds of hospitalisation were 50% to 79% greater. Former smokers had a 10% higher risk of outpatient visits than men who had never taken up the habit.
Smoking linked to increase in diabetes outpatient visits
Among women, smoking was linked to a one-quarter to one-third increase in the risk of outpatient visits for diabetes, and a 43% to 65% increase in the odds of hospitalisation. Former smokers had a 19% higher risk of outpatient visits and a 31% greater chance of hospitalisation than never-smokers.
The researchers acknowledge some limitations of the study. Besides the fact that it cannot prove smoking directly raises diabetes risk, it is not clear how broadly the findings can be extended. The data, Jee's team notes, come from a largely middle-class, employed group, who may not be representative of the entire Korean population or those of other countries.
However, they conclude, "the mounting evidence on smoking and diabetes, particularly in Asians, suggests that smoking should be considered as a potentially reversible cause of diabetes." (Reuters Health/ September 2010)
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