A new study shows that smoking tobacco changes body fat distribution and appears to especially increase the amount of abdominal fat and fat around the organs, which really harms health. A researcher says that this may give smokers extra motivation to stop.
Many people know that quitting smoking can lead to gaining a few kilos – which can even make some smokers drop the idea of giving up the habit.
Nevertheless, a new study shows that the association between smoking and body fat is not quite as straightforward as many may have thought.
The study shows that smoking changes the distribution of body fat and is associated with increased abdominal fat and fat around the organs. Such visceral fat can harm health and be associated with the development of an increased risk of developing type 2 diabetes, cardiovascular disease and other diseases.
“This study reinforces previous research. We know that smoking is unhealthy, and we also know that many people do not want to stop smoking because they are afraid of gaining weight. Now, we can tell them that smoking increases abdominal fat and visceral fat around the organs. This is important to highlight because it might motivate some people to decide to quit smoking,” explains Germán Carrasquilla, a researcher involved in the study and Assistant Professor, Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Denmark.
The research has been published in Addiction.
Data from large genome-wide studies
Research on the associations between smoking and body fat distribution has pointed in different directions.
Quitting smoking is widely known to lead to weight gain, but some studies have found that smoking is associated with increased abdominal fat.
However, these studies have had difficulty in adjusting for other confounders, such as whether smoking is also associated with less physical activity, an unhealthier diet or alcohol consumption.
To improve understanding of the association between smoking and body fat composition, the researchers investigated the link between genetic predisposition to smoking and the body fat distribution through Mendelian randomisation for estimating causality.
The researchers used data from genome-wide association studies from several of the world’s largest studies from the Sequencing Consortium of Alcohol and Nicotine use, the Genetic Investigation of Anthropometric Traits Consortium and the UK Biobank.
In total, the researchers had genetic data on the predisposition to start smoking for 1,232,091 people; genetic predisposition for lifetime smoking for 462,690 people; and genetic predisposition for the quantity of smoking for 337,334 people.
They also had information on waist-to-hip ratio and waist and hip circumference with and without adjustment for body mass index.
“Previous studies have investigated how one genetic variant linked to smoking is associated with body fat composition. In this study, we examined multiple genetic variants and various methods to achieve a more robust result. Smoking is polygenic, and we therefore took a step further and examined several genetic signals associated with smoking,” says Germán Carrasquilla.
Smoking increases fat around the organs
The results show that genetic predisposition to start smoking and lifetime smoking are associated with increased abdominal fat measured as a higher waist-to-hip ratio among people with a genetic predisposition to smoking.
In a subanalysis, the researchers also examined abdominal fat composition and found that the differences in genetic liability for smoking and abdominal fat were associated with increased visceral fat.
“Excessive visceral fat is a significant health problem because it is a risk factor for developing metabolic and cardiovascular diseases. Similarly, smoking is detrimental to health not only because it directly damages the lungs and elevates the risk of cardiovascular disease and cancer, but also because it increases visceral fat, further exacerbating these health issues,” explains Germán Carrasquilla.
The biology remains hidden
Germán Carrasquilla says that future research will aim to identify the biological mechanisms that link smoking to more abdominal fat.
Previous observational studies suggest that smoking affects body fat distribution by changing hormones such as cortisol or sex hormones, but the new study could not support this hypothesis.
“More research is needed to understand the biology behind this association,” explains Germán Carrasquilla.
He points out that the study perspective is that people should know that they might gain a few kilos when they quit smoking, but the fat distribution appears to be healthier than if they continue to smoke.
“Our findings also challenge the common paradigm that quitting smoking may lead to weight gain. It is crucial to emphasise that the health benefits of quitting smoking far outweigh the risks of continued smoking. The fact that smoking increases the problematic intra-abdominal fat may motivate some individuals to quit, since they recognise that stopping smoking is invariably better for their health than continuing,” concludes Germán Carrasquilla.
“Estimating causality between smoking and abdominal obesity by Mendelian randomization” has been published in Addiction. The authors are affiliated with the Novo Nordisk Foundation Center for Basic Metabolic Research at the University of Copenhagen and the Novo Nordisk Foundation Center for Genomic Mechanisms of Disease at the Broad Institute of MIT and Harvard, Cambridge, MA, USA.
