**Summary**
A new study from Aarhus University reveals a direct link between smoking and an increased risk of mental illnesses like depression and bipolar disorder. The research, based on data from 350,000 individuals from the UK Biobank, shows that smoking increases the risk of hospitalization for mental illness by 250%. Importantly, the study finds that smoking typically precedes mental illness, often by a significant time gap. The research not only clarifies the role of smoking in mental illness but also raises questions about raising the legal age for cigarette purchase.
**Key Facts**
– Smoking increases the risk of being hospitalized for a mental illness by a staggering 250%.
– People generally start smoking around the age of 17 but are not hospitalized for mental disorders until after 30, indicating that smoking likely precedes mental illness.
– Genetic data suggests that certain “smoking-related genes” may increase the risk of both smoking and mental disorders, although the precise biological mechanism remains unclear.
**Introduction**
In recent years, research has indicated a strong correlation between smoking and mental illness. However, researchers have not been able to agree on whether smoking causes depression or other mental disorders, or whether we smoke because we need to lessen the symptoms of a latent mental disorder. Together with two colleagues from Canada, Doug Speed from the Center for Quantitative Genetics and Genomics at Aarhus University has shown that smoking can lead to depression and bipolar disorder.
**Research Methodology**
To answer whether smoking causes mental disorders, researchers needed a large volume of data. They gained access to the UK Biobank, which contains genetic data on more than half a million people. The genetic data was paired with other health information and lifestyle answers provided by the participants. The researchers fed the data into a computer and looked for patterns. They found that people typically start smoking before the age of 20 but are not admitted to the hospital with a mental disorder until they’re between 30 and 60 on average.
**Genetic Factors and Smoking**
As many as 90% of the people in the data set who were still smokers or former smokers started before the age of 20. Twin studies show that genes can explain 43% of the risk of becoming a smoker. People who carried the genetic variants associated with smoking but did not smoke were less likely to develop mental disorders.
**Possible Biological Mechanisms**
The study does not provide a definitive explanation for how smoking causes mental disorders. One theory is that nicotine inhibits the absorption of the neurotransmitter serotonin in the brain, and people with depression do not produce enough serotonin. Another theory suggests that smoking causes inflammation in the brain, which can damage parts of the brain and lead to mental disorders.
**Raising the Age Limit for Buying Cigarettes**
The study shows that people rarely start smoking after the age of 20. Therefore, raising the age limit for buying cigarettes may prevent people from starting smoking. The researchers suggest that changing the law and raising the age limit might have an effect on reducing smoking rates.
**Conclusion**
The study provides evidence for a direct link between smoking and an increased risk of mental illnesses like depression and bipolar disorder. The research shows that smoking typically precedes mental illness, often by a significant time gap. Genetic factors also play a role in both smoking and mental disorders, with certain “smoking-related genes” increasing the risk for both. The study raises questions about raising the legal age for cigarette purchase as a potential strategy to reduce smoking rates. Further research is needed to understand the biological mechanisms through which smoking leads to mental illness.
Dr Megan Johnson, MD, Cure of Mind
