Smoking Linked to Increased Adipose Tissue Volume, Even with Lower BMI

Despite having a lower body weight, new research indicates patients who smoke were at a higher risk of depositing fat in and around organs and tissues compared to nonsmokers.

An analysis of data from computed tomography (CT) scans more than 3000 patients in the Coronary Artery Risk Development in Young Adults (CARDIA) study, results indicate smokers had greater volumes of intermuscular adipose tissue and lower muscle quality than never smokers despite maintaining a low BMI, which could signal increased risk of cardiovascular disease and age-related physical deconditioning.

"We found that current smokers had abdominal muscles that were significantly higher in fat," said lead investigator James G. Terry, research programs manager in Radiology and member of Vanderbilt Translational and Clinical Cardiovascular Research Center (VTRACC), in a statement. "Smokers also had a higher proportion of visceral fat, the fat around their internal organs, compared to never smokers, whereas those who had quit smoking had intermediate levels of visceral and intramuscular fat.”

Despite public health initiatives and efforts to convey the risks of smoking, clinicians sometimes encounter patients who consider the lower risk of obesity seen amongst smokers as a benefit. Even with this apparent decrease in obesity, some previous studies have suggested smoking was associated with higher central adiposity and ectopic adipose deposition.

With no consensus into the effects of smoking on adipose tissue volumes, Terry and team of investigators sought to test the hypothesis that smokers have higher abdominal intermuscular adipose tissue and lower lean muscle quality than never smokers. To do so, they designed their analysis using measurement data from CT scans of middle-aged CARDIA participants. Specifically, investigators hoped to measure the patients volumes of subcutaneous fat, visceral fat, intermuscular fat, and intramuscular fat from CT scans in year 25 of the study.

For CARDIA participants to be included in the current analysis, they needed to be examined in clinic at year 25, have undergone abdominal CT, and could not be pregnant. In total, 3020 of the original 5115 CARDIA participants were included in the current analysis.

At the year 25 visit, 1552 of the 3020 participants were never smokers, 944 were former smokers, and 524 were current smokers. When comparing the groups, investigators found current smokers were less likely to be female or white, had fewer years of education, were less physically active, had higher alcohol intake, and were more likely to consume sugar-sweetened beverages and fasted food than never smokers.

These comparisons also suggested current smokers had lower BMIs than never smokers. However, current smokers had increased rates of hypertension, triglycerides, and C-reactive protein than never smokers.

In fully adjusted multivariable models, which accounted for confounders such as BMI and cardiovascular disease risk factors, the mean intermuscular adipose tissue volume was 2.66 (95% CI, 2.55–2.76) cm³ among current smokers, 2.36 (95% CI, 2.29–2.43) cm³ in former smokers, and 2.23 (95% CI, 2.18–2.29) cm³ in never smokers. Additionally, the multivariable models also indicated current (40.4 [39.9–40.9] Hounsfield units [HU]) and former smokers (40.8 [40.5–41.2] HU) had lower mean muscle attenuation than never smokers (41.6 [41.3–41.9] HU), which investigators note is suggestive of lower muscle quality.

Investigators also pointed out an association between pack-years of smoking exposure were directly associated with intermuscular adipose tissue volume (β [95% CI]: 0.017 [0.010–0.025]) (P <.001).

This study, “Association of smoking with abdominal adipose deposition and muscle composition in Coronary Artery Risk Development in Young Adults (CARDIA) participants at mid-life: A population-based cohort study,” was published in PLOS Medicine.