Can Smoking Cause Depression?
Researchers have made bold claims about cigarette smoking leading to depression. It has long been known that smokers have higher rates of depression than nonsmokers, but researchers from the University of Otago in New Zealand investigated the link further, and say they have found a causal relationship.
The team took figures from over 1,000 men and women aged 18, 21 and 25 years. Smokers had more than twice the rate of depression. Using a computer modeling approach, their analysis supported a pathway in which nicotine addiction leads to increased risk of depression.
In the British Journal of Psychiatry, the researchers wrote, “The best-fitting causal model was one in which nicotine dependence led to increased risk of depression.” They suggest two possible routes, one involving common risk factors, and the second a direct causal link.
According to the researchers, “this evidence is consistent with the conclusion that there is a cause and effect relationship between smoking and depression in which cigarette smoking increases the risk of symptoms of depression.”
Professor David Fergusson, the study’s lead researcher, said, “The reasons for this relationship are not clear. However, it’s possible that nicotine causes changes to neurotransmitter activity in the brain, leading to an increased risk of depression.” But he adds that the study “should be viewed as suggestive rather than definitive.”
Writing in the same journal, Marcus Munafo, PhD of Bristol University, UK, reports that cigarette smokers often talk about the antidepressant benefits of smoking. “But evidence suggests that cigarette smoking may itself increase negative affect [emotion], so the causal direction of this association remains unclear,” he writes.
As Munafo points out, the role of nicotine in depression is complex, because smokers often feel emotionally uplifted following a cigarette. Bonnie Spring, PhD, at Hines Hospital, VA Medical Center, Illinois, looked at the link. Spring explains that depression-prone smokers are thought to self-administer nicotine to improve mood. But little evidence supports this view, so she examined nicotine’s effect on depression.
Her team recruited 63 regular smokers with no history of diagnosed depression, 61 with past but not current depression, and 41 with both current and past depression. All were given either a “nicotinized” or a “denicotinized” cigarette following a positive mood trigger.