News Author: Laurie Barclay, MD

April 10, 2006 — Both active and passive smoking increase the risk of developing glucose intolerance, according to the results of a prospective cohort study reported in the April 6 Online First issue of the BMJ.

"Smoking has been linked to impaired response to glucose tolerance tests and insulin resistance," write Thomas K. Houston, MD, from the Birmingham Veterans Affairs Medical Center in Alabama, and colleagues. "Although smoking cessation can result in modest weight gain, smoking is related to a more unhealthy distribution of upper body weight and greater waist:hip ratio. Smoking has also been associated with risk of chronic pancreatitis and pancreatic cancer, suggesting that tobacco smoke may be directly toxic to the pancreas."

The Coronary Artery Risk Development In young Adults (CARDIA) study began in 1985 to 1986 with recruitment of black and white men and women aged 18 to 30 years with no glucose intolerance at baseline. Participants were 1386 current smokers, 621 previous smokers, 1452 never smokers with reported exposure to secondhand smoke (validated by serum cotinine concentrations, 1 - 15 ng/mL), and 1113 never smokers with no exposure to secondhand smoke. The primary endpoint was time to development of glucose intolerance (glucose, >/= 100 mg/dL or taking antidiabetic drugs) during 15 years of follow-up.

At baseline, median age was 25 years, 55% of participants were women, and 50% were African American. During follow-up, glucose intolerance developed in 16.7% of participants. There was a graded association between smoking exposure and the incidence of glucose intolerance during the 15-year follow-up, which was 21.8% for smokers, 17.2% for never smokers with passive smoke exposure, 14.4% for previous smokers, and 11.5% for never smokers with no passive smoke exposure.

After adjustment for multiple baseline sociodemographic, biological, and behavioral factors, risk was still higher in current smokers (hazard ratio [HR], 1.65, 95% confidence interval [CI], 1.27 - 2.13) and never smokers with passive smoke exposure (HR, 1.35; 95% CI, 1.06 - 1.71) than in never smokers without passive smoke exposure. However, risk in previous smokers was similar to that in never smokers without passive smoke exposure.

"We found that tobacco exposure is associated with the development of glucose intolerance over a 15 year period, with a dose-response effect apparent," the authors write. "These findings support a role of both active and passive smoking in the development of glucose intolerance in young adulthood."

Study limitations include potential residual confounding, observational nature, and recruitment of African Americans and white people from 4 US urban areas, limiting generalizability.

"Importantly, we identified passive tobacco exposure in never smokers as a new risk factor for glucose intolerance," the authors conclude. "If confirmed by further research, these findings provide further documentation of the deleterious effects of tobacco smoking, and policy makers may use them as additional justification to reduce exposure to passive smoke."