April 6, 2006 -- For the first time, researchers report a possible link between secondhand smoke and glucose intolerance.

The study, published in BMJ Online First, doesn't prove that secondhand smoke causes glucose intolerance. But it does show an association between tobacco exposure -- including nonsmokers exposed to secondhand smoke -- and glucose intolerance.

Thomas Houston, MD, MPH, of Alabama's Birmingham Veterans Affairs Medical Center, helped conduct the study. He and his colleagues studied more than 4,600 young blacks and whites for 15 years.

Current cigarette smokers were most likely to develop glucose intolerance, which was defined as having diabetes or impaired fasting glucose (blood sugar). Having impaired fasting glucose is also referred to as prediabetes. Nonsmokers reporting secondhand-smoke exposure came in second, followed by former smokers. Nonsmokers without secondhand-smoke exposure were least likely to develop glucose intolerance, the study shows.

About the Participants

The group was equally split between blacks and whites. Fifty-five percent were women.

Participants had enrolled in a larger study on heart health. They lived in four cities: Chicago; Minneapolis; Birmingham, Ala.; and Oakland, Calif.

When the study started, participants were 18-30 years old and didn't have glucose intolerance. They got an initial checkup lasting four or five hours and were interviewed about smoking.

The group included 1,386 current smokers, 621 former smokers, 1,452 smokers who reported secondhand-smoke exposure, and 1,113 nonsmokers who reported no secondhand-smoke exposure. To try to make sure that nonsmokers really weren't smokers, the researchers checked participants' blood for a marker of nicotine.

Participants got follow-up interviews by telephone every year. They were also scheduled for in-person checkups two, five, seven, 10, and 15 years into the study.

Other Influences

The researchers gathered lots of other information about participants, including diet habits, waist-to-hip ratio, blood pressure, alcohol use, physical activity, income, and education.

Those factors might affect a person's risk of developing glucose intolerance and varied among participants. For instance, current smokers had lower education and consumed more fat and alcohol than nonsmokers with no secondhand-smoke exposure.

The researchers took those and other factors into account. The study's main findings didn't change, but Houston's team doesn't rule out other possible influences, since observational studies can't prove cause and effect.

The findings should be checked in other groups of people, write Houston and colleagues. They note mixed results in other studies on tobacco exposure and diabetes risk.

SOURCES: Houston, T. BMJ Online First, April 7, 2006. News release, BMJ.

Reviewed by Louise Chang