Study challenges belief that lower BMI shields smokers from health risks

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Some smokers rationalise continuing to smoke because of lower body weight often associated with the habit. However, Vanderbilt University Medical Center investigators have determined that even with a lower body mass index or BMI, smokers have a higher risk of depositing fat in and around organs and tissues compared to those who never smoked.

This is concerning because excess fat, also known as adipose tissue, deposited in the abdomen and around organs such as the liver and non-adipose tissues including muscles, may disrupt their normal functions and cause health problems.

This disruption is associated with a higher risk for health complications such as cardiovascular disease and type 2 diabetes, according to material produced by Vanderbilt University. The study was published by the open access journal PLOS Medicine on 21 July.

Investigators used computed tomography (CT) body scans to measure abdominal fat deposited just below the skin’s surface (subcutaneous fat), around organs including the intestines (visceral fat) and abdominal muscles (intermuscular fat), and inside the muscles (intramuscular fat) in 3,020 middle-aged participants in the federally funded Coronary Artery Risk Development in Young Adults (CARDIA) study.

“We found that current smokers had abdominal muscles that were significantly higher in fat,” said lead author James ‘Greg’ Terry, research programs manager in radiology and member of the Vanderbilt Translational and Clinical Cardiovascular Research Center (VTRACC).

“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.

“This might contribute to the higher prevalence of cardiovascular disease and age-related physical deconditioning and disability that is well-documented among those who smoke.”

Co-author Dr David Jacobs, professor of Public Health at the University of Minnesota and one of the founding CARDIA investigators, said he considers “cigarette smoking as a weight-loss tool to be a risky strategy. Our data show that the fat deposition pattern apparent in smokers is associated with metabolic damage.”

The longitudinal CARDIA study was begun in 1985 with the recruitment of young adult participants (aged 18-30), equally balanced by male and female sex and black and white race, at four locations in the United States. The CT measurements were taken at the 25-year mark.

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

PLOS Medicine. Published on 21 July 2020. 

Authors

James G Terry, Katherine G Hartley, Lyn M Steffen, Sangeeta Nair, Amy C Alman, Melissa F Wellons, David R Jacobs Jr, Hilary A Tindle and John Jeffrey Carr.

Abstract

Smokers have lower risk of obesity, which some consider a “beneficial” side effect of smoking. However, some studies suggest that smoking is simultaneously associated with higher central adiposity and, more specifically, ectopic adipose deposition. Little is known about the association of smoking with intermuscular adipose tissue (IMAT), an ectopic adipose depot associated with cardiovascular disease (CVD) risk and a key determinant of muscle quality and function.

We tested the hypothesis that smokers have higher abdominal IMAT and lower lean muscle quality than never smokers.

Methods and findings

We measured abdominal muscle total, lean, and adipose volumes (in cubic centimeters) and attenuation (in Hounsfield units [HU]) along with subcutaneous (SAT) and visceral adipose tissue (VAT) volumes using computed tomography (CT) in 3,020 middle-aged Coronary Artery Risk Development in Young Adults (CARDIA) participants (age 42–58, 56.3% women, 52.6% white race) at the year 25 (Y25) visit.

The longitudinal CARDIA study was initiated in 1985 with the recruitment of young adult participants (aged 18–30 years) equally balanced by female and male sex and black and white race at 4 field centers located in Birmingham, AL, Chicago, IL, Minneapolis, MN, and Oakland, CA. Multivariable linear models included potential confounders such as physical activity and dietary habits along with traditional CVD risk factors. Current smokers had lower BMI than never smokers.

Nevertheless, in the fully adjusted multivariable model with potential confounders, including BMI and CVD risk factors, adjusted mean (95% CI) IMAT volume was 2.66 (2.55–2.76) cm3 in current smokers (n = 524), 2.36 (2.29–2.43) cm3 in former smokers (n = 944), and 2.23 (2.18–2.29) cm3 in never smokers (n = 1,552) (p = 0.007 for comparison of former versus never smoker, and p < 0.001 for comparison of current smoker versus never and former smoker). Moreover, compared to participants who never smoked throughout life (41.6 [41.3–41.9] HU), current smokers (40.4 [39.9–40.9] HU) and former smokers (40.8 [40.5–41.2] HU) had lower lean muscle attenuation suggesting lower muscle quality in the fully adjusted model (p < 0.001 for comparison of never smokers with either of the other two strata).

Among participants who had ever smoked, pack-years of smoking exposure were directly associated with IMAT volume (β [95% CI]: 0.017 [0.010–0.025]) (p < 0.001). Despite having less SAT, current smokers also had higher VAT/SAT ratio than never smokers. These findings must be viewed with caution as residual confounding and/or reverse causation may contribute to these associations.

Conclusions

We found that, compared to those who never smoked, current and former smokers had abdominal muscle composition that was higher in adipose tissue volume, a finding consistent with higher CVD risk and age-related physical deconditioning. These findings challenge the belief that smoking-associated weight loss or maintenance confers a health benefit.

 

Study challenges idea that lower BMI shields smokers from fat-associated health risks

 

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

 


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