Smoking Could Raise Risk of Developing Depression and Schizophrenia

Smoking could raise the risk of developing depression and schizophrenia, according to research.

The study involved 462,690 people of European descent with an average age of 56, who were taking part in the U.K. Biobank study. Of the total, 8 percent said they currently smoked, 22 percent were former smokers, and 30 percent had smoked at some point in their lives.

By looking at the participants' genes, researchers found smoking tobacco appeared to increase their risk of developing depression and schizophrenia. In addition, the results revealed those with these mental conditions are also more likely to smoke in the first place.

Study co-author Robyn Wootton, a researcher at the University of Bristol School of Psychological Science, told Newsweek that smoking is already known to be bad for our physical health.

"But this study shows that smoking also has detrimental effects on mental health, further stressing the importance that individuals should not smoke," she said.

"For individuals already suffering with a mental illness, it is a commonly held belief that smoking is a form of 'self-medication' and therefore individuals with mental health problems are often not helped to quit as much as they should be," explained Wootton.

Asked whether similar links have been found in other conditions, such as anxiety or OCD, Wootton said the team has yet to explore the potential associations, but said they "would be really interesting analyses to do in the future."

Earlier this year, the researchers similarly found a link between smoking and bipolar disorder, but no clear evidence that the risk for bipolar disorder increases smoking behaviour. The findings were published in the British Journal of Psychiatry.

Next, the team hopes to uncover the mechanism linking smoking and poor mental health.

"We think it could be due to nicotine leading to disregulation of pathways in the brain that are also involved in mental illness. But we would like to explore this in more detail," said Wootton.

Explaining the methodology of both studies, Wootton said much research has explored the link between smoking and mental health, but it's unclear whether smoking exacerbates such conditions or if those with them are more likely to smoke.

"The method of Mendelian randomisation can get around the issue of these group differences by using genetic variants that predispose some individuals to smoke more and others to smoke less. These genetic variants are specific to smoking (not alcohol or diet, etc.) and therefore this is a kind of natural experiment where we can look at the effect of smoking independent of other behaviours," she said.
Wootton continued: "Being the first to apply this method to understand the link between smoking and mental health, we found evidence for causal effects in both directions such that smoking increased risk of developing depression and or schizophrenia and also that having depression and or schizophrenia increased smoking behaviour."