MONDAY, June 7, 2004 (HealthDayNews) -- Smokers already worried about their risks for cancer and heart disease now have another reason to quit: Tobacco may raise the risk for type 2 diabetes, say two new studies.
"This increased risk for type 2 diabetes could be due to increased insulin resistance, which has previously been shown to occur after an acute episode of smoking," said Dr. Valdemar Grill, a professor at both the University of Science and Technology in Trondheim, Norway, and the Karolinska Institute in Stockholm, Sweden.
He presented the findings of the first study on June 7 at the annual meeting of the American Diabetes Association (ADA) in Orlando, Fla. A second study presented by Johns Hopkins researchers at the meeting came to the same conclusion.
Experts have long understood that smoking does serious damage to arteries while raising risks for lung cancer. But studies are beginning to suggest it may encourage the development of diabetes, too.
In the latest study, Grill and his colleagues analyzed Norwegian government health data on nearly 39,000 adult men and women tracked over a period of 11 years.
They found that, regardless of gender, age, weight, physical activity and use of alcohol, smokers who smoked at least a pack of cigarettes a day faced a 64 percent higher risk of developing type 2 diabetes compared with nonsmokers.
The vast majority of diabetics -- about 95 percent -- are affected by type 2 diabetes, which develops when the pancreas fails to produce enough insulin to meet the body's demand or when body tissues become resistant to the effects of insulin. As insulin fails, blood sugar rises to unhealthy levels, raising the risks for cardiovascular disease and other health problems. Experts estimate that more than 18 million Americans have diabetes.
According to Grill, previous studies have suggested smoking contributes to insulin resistance. And since similar associations were found in people who used smokeless "snuff" tobacco, "it is likely that it is nicotine, the common substance in cigarettes and snuff, that is the culprit," he said.
"It is also possible that nicotine has a negative effect on insulin secretion," Grill added. "We have some data in animals to support this notion."
Curiously, the Norwegian study also found smoking was associated with lowered risks for two more rare forms of diabetes -- autoimmune diabetes (associated with dysfunction in the immune system), and type 1 diabetes. According to Grill, animal studies have suggested nicotine may actually help prevent the triggers behind autoimmune diabetes.
The risks far outweigh this potential minor benefit, however, and Grill strongly advises that all smokers "stop smoking because of the many proven and grave health hazards" associated with the habit.
Another study presented at the meeting seemed to back up the Norwegian findings. Researchers led by Dr. Hsin-Chieh Yeh of the Johns Hopkins School of Public Health examined data on nearly 9,000 older U.S. adults tracked for nine years.
They found that after adjusting for age, sex, race, weight and other factors, long-term smokers faced a 50 percent higher risk of developing diabetes compared with people who never smoked -- with risks rising as the number of years spent smoking increased.
Commenting on the two studies, Dr. Nathaniel Clark, the ADA's national vice president for clinical affairs, admitted he was "a little surprised" by the findings.
"When we usually list the risk factors for diabetes, smoking is never on that list. In that sense, this is new information," he said.
Although the findings are too preliminary to prompt any change in official ADA policy when it comes to preventing diabetes, Clark said quitting smoking should be a no-brainer.
"There are so many reasons not to smoke. I can't imagine that a fear of developing diabetes would trump dying from lung cancer, or any of the other terrible things smoking does," he said.
For more on diabetes, visit the American Diabetes Association.