Continuous secondhand smoke exposure ups risk of obesity in boys

Boys with sustained exposure to secondhand smoke are at increased risk of obesity, as reported in a study.

The study used population-based longitudinal data of primary school students in Adachi City, Tokyo, Japan. Researchers applied ordinal logistic regression models to evaluate the association of patterns of secondhand smoke exposure (eg, continuous, quit, start, or never exposed) from 4th to 6th grade to body mass index (BMI) categories (underweight or normal weight, overweight, obesity) in 6th grade.

A total of 3,605 students (50 percent boys) were included in the analysis. Exposure to secondhand smoke continued in 4th and 6th grade in 15.2 percent of the students, ceased from 4th to 6th grade in 5.8 percent, and started from 4th to 6th grade in 4.8 percent. Most of the students (74.1 percent) were not exposed to secondhand smoke in 4th and 6th grade.

In 6th grade, 18.0 percent of the students were overweight (BMI 1–2 SD) while 7.2 percent had obesity (BMI >2 SD). The corresponding proportion of patients with overweight and obesity in 4th grade were 14.5 percent and 5.5 percent.

Continuous secondhand smoke exposure was associated with higher odds of being in the high BMI category compared with nonexposure (odds ratio [OR], 1.51, 95 percent confidence interval [CI], 1.16–1.96). This association was evident in boys (OR, 1.74, 95 percent CI 1.25–2.44) but not in girls (OR, 1.14, 95 percent CI, 0.74–1.76).

On the other hand, students in the quit-exposure group did not have greater odds of being in the high BMI category relative to the no-exposure group (OR, 1.11, 95 percent CI, 0.75–1.66). This was true for boys (OR, 1.46, 95 percent CI, 0.88–2.41).

More research is required to confirm the preventive effect of secondhand smoke exposure discontinuation on obesity risk and examine sex differences in obesity risk by secondhand smoke exposure.