14 DAY TRIAL // A paper published in the latest issue of Journal of Psychiatric Research demonstrates that people who smoke tobacco are three times more likely to develop symptoms related to major depression disorder than those who do not smoke.
The study was conducted on heavy smokers, a subgroup of the population that was demonstrated to be statistically more likely to become depressed than their peers. However, the correlation has never been proven entirely. This study doesn't settle the debate, but it does bring some evidence to support the link.
One of the most interesting conclusions in the new study is that current smokers are also 300 percent more likely to develop MDD than former heavy smokers. This suggests that smoking is an ongoing risk factor, which can be eliminated by simply quitting the habit.
The correlation between smoking and depression is nothing new. What is new is the shift from the “shared-vulnerability” hypothesis to a causal relationship between the two.
“Under the shared-vulnerability hypothesis, ever-heavy smokers may be expected to have similar elevated risk for major depressive episode irrespective of their smoking status during follow-up. Our results point to the contrary,” Salma Khaled, PhD, explains.
She conducted the investigation while based at the Mental Health Center for Research and Teaching. Her team used data from the Canadian National Population Health Survey for this research. This information covered 3,824 adults, PsychCentral reports.
“Ever-heavy smokers (current and former) may share similar genetic, behavioral, and environmental vulnerabilities, at least for heavy smoking initiation,” Khaled adds. She is now based at the University of Calgary, in Canada.
“Our findings are consistent with the view that the heavy smoking-to-major depression pathway is causal in nature, rather than mainly due to confounding by shared vulnerability factors,” the researcher goes on to say.
A statistical analysis of the study data revealed that former heavy smokers' risk of developing MDE decreased proportionally to the amount of time that had passed since they quitted the habit. This further contributed to strengthening the case for a causal relationship between the two.