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 The findings might indicate that extra body fat influences the
likelihood of taking up smoking and how heavily a person smokes, or
that the urges to overeat and to smoke may share some genetic
origins, the authors note in The BMJ.
"These results highlight the role of obesity in influencing smoking
initiation and cessation, which could have implications for public
health interventions aiming to reduce the prevalence of these
important risk factors," writes the study team, led by Robert
Carreras-Torres at the International Agency for Research on Cancer
in Lyon, France.
The authors did not respond to a request for comments.
The researchers analyzed data from the UK Biobank and the TAG
Consortium on more than 450,000 people of European descent. These
databases contain genetic, medical and lifestyle information for
their volunteer participants.
Past studies, the authors note, have already linked genetic
variations known as SNPs to both obesity and smoking, suggesting
that particular SNPs increase a person's vulnerability to both forms
of "addictive behavior" - overeating and smoking. It's not clear,
however, if people who smoke stay thinner because smoking curbs
appetite, or even if smokers really do stay thin.
To avoid the confusing influence of smoking's effect on appetite,
the researchers didn't just look at participants' actual body mass
and other body fat measurements. They also created a genetic profile
of predicted body traits based on a person's SNPs. Using both real
measurements and this genetic profile, the team then analyzed each
person's smoking history.
For actual body mass index (BMI), a measure of weight relative to
height, the researchers found that every additional 4.6
kilograms/meter squared was associated with a 5 percent lower risk
of being a current smoker but also a 12 percent higher risk of ever
having been a smoker, compared to never-smokers.
The same real-BMI increment was also linked to a smoking-intensity
increase of 1.75 cigarettes per day for current and former smokers
combined.
When researchers looked at the genetic body fat profile, however,
they found that each incremental increase in projected BMI based on
SNPs was linked to 24 percent higher odds of being a current smoker
and an 18 percent increase in odds of being a former smoker.
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Projected increases in waist circumference and body fat percentage
based on genetic profile were similarly linked with increases in the
odds of ever having smoked and increased smoking intensity.
Genetic body type was not linked with odds of smoking cessation,
though. This detail and others lead the authors to suggest that
rather than genetic predisposition to addictive behavior, excess
body fat itself might influence cravings for nicotine.
Whatever the relationship between excess body fat and smoking,
interventions to help people avoid these health risks need to take
both into account, the authors conclude.
People may be tempted to start smoking to help them lose weight,
said Lucy Popova, a researcher at the Georgia State University
School of Public Health in Atlanta who wasn't involved in the
research. Smoking decreases appetite because nicotine, the primary
addictive chemical in tobacco, activates various receptors in the
brain, and some of these receptors are on the nerve cells that
regulate appetite and eating behavior, she said.
"Starting smoking in order to lose weight is a really bad idea. On
one hand, you might weigh a couple of pounds less, but this weight
reduction might come from lean muscles and not fat," Popova said.
Also, research shows that smokers, while having lower BMI, tend to
have more fat around their abdomens than non-smokers, which is worse
for health than simply having a high BMI, she said.
"On the other hand, smoking causes cancers, heart diseases, stroke,
bad breath, yellow teeth, and all sorts of other negative
consequences, including death. Smokers also have a harder time
exercising due to the shortness of breath, so this makes losing
weight even more difficult," Popova noted.
SOURCE: https://bit.ly/2KAirHd The BMJ, online May 16, 2018.
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