If you need another reason to steer clear of cigarette smoke, consider this: a new study presented at a conference this week suggests breathing in secondhand smoke is linked to higher risks of developing type 2 diabetes and obesity.

Presented on Sunday at The Endocrine Society’s 94th Annual Meeting in Houston, the findings show that adults exposed to secondhand smoke have higher rates of these diseases than non-smokers who are not exposed to tobacco smoke.

Co-author Dr Theodore C Friedman, chairman of the Department of Internal Medicine at Charles R Drew University in Los Angeles, told the press:

“More effort needs to be made to reduce exposure of individuals to secondhand smoke.”

For the study, Friedman and colleagues used data from a nationally representative sample of more than 6,300 adults who took part in the US National Health and Nutrition Examination Survey (NHANES) between 2001 and 2006.

As well as answering questions about smoking, the participants had also given blood samples, from which various measures were taken, including levels of cotinine, an alkaloid found in tobacco that is also a metabolic byproduct of nicotine. The researchers used this to verify passive smoking exposure.

Friedman explained that while other studies have shown a link between type 2 diabetes and secondhand or passive smoking, none of them had used a blood marker to confirm the results.

25% of the participants in Friedman’s study were current smokers, which he and his colleagues classed as those participants who said “yes” when asked “Do you smoke cigarettes?” and whose cotinine levels were above 3 nanograms per milliliter (ng/mL).

41% of the sample were classed as non-smokers. These were participants who answered “no” when asked “Do you smoke cigarettes?”, and whose cotinine levels were under 0.05 ng/mL.

34% of the sample were classed as secondhand smokers. These had also answered “no” to the current smoking question, but their blood cotinine levels were above 0.05 ng/mL.

After adjusting the results to rule out any effects from age, sex, race, alcohol consumption and exercise, the researchers found that compared to non-smokers, secondhand smokers showed signs of a number of factors that can lead to type 2 diabetes, such raised insulin resistance, elevated fasting blood glucose or blood sugar, and higher hemoglobin A1c, a measure of blood sugar control over the past three months.

Secondhand smokers also had a higher rate of type 2 diabetes, which the researchers classed as having a hemoglobin A1c count above 6.5%. The rate of type 2 diabetes in the secondhand smokers was similar to that of the current smokers, said the researchers.

Levels of Body Mass Index (BMI), a measure of obesity, were higher among secondhand smokers than non-smokers, and although current smokers had lower BMI, their higher hemoglobin A1c was higher.

And when they adjusted the figures to rule out the effect of BMI, Friedman and colleagues found that levels of hemoglobin A1c in secondhand smokers and current smokers were still higher than in non-smokers.

Friedman said these results show “that the association between secondhand smoke and type 2 diabetes was not due to obesity“.

He called for further studies to investigate whether secondhand smoke actually causes type 2 diabetes.

Written by Catharine Paddock