Secondhand smoke is associated with abdominal obesity and high obesity index in a large Taiwanese population study

Abdominal obesity is an increasingly critical global public health concern. Previous studies have shown a relationship between secondhand smoke (SHS) exposure and obesity, however direct comparisons of the effects of smoking and SHS exposure on abdominal obesity are limited. This study aimed to examine the relationships between smoking and SHS exposure on abdominal obesity and obesity indices. We enrolled 121,364 participants from the Taiwan biobank and categorized them into three groups: never-smokers who had not been exposed to SHS (n = 81,315), never-smokers who had been exposed to SHS (n = 6982), and ever-smokers (n = 33,067). SHS exposure was assessed using self-reported questionnaires. Abdominal obesity was defined as a waist circumference > 80 cm for women and > 90 cm for men. The following obesity indices were calculated: body mass index, waist-hip ratio, waist-height ratio, abdominal volume index, conicity index, triglyceride-glucose index, and visceral adiposity index. After multivariable adjustment, compared to no SHS exposure, SHS exposure (odds ratio [OR]  1.169; 95% confidence interval [CI]  1.106-1.235; p < 0.001) and ever-smokers (OR   1.154; 95% CI   1.115-1.194; p < 0.001) were significantly associated with abdominal obesity. Furthermore, SHS exposure and ever-smokers were associated with high values of all the studied obesity indices. This study highlights a strong association between SHS exposure and abdominal obesity, with risks comparable to or exceeding those of smoking. Both SHS exposure and ever-smokers were associated with high obesity indices. Our findings emphasize the need for public health management to reduce SHS exposure and prevent obesity.