Smoking and the risk for bipolar disorder: evidence from a bidirectional Mendelian randomisation study.

Abstract

BACKGROUND:

There is increasing evidence that smoking is a risk factor for severe mental illness, including bipolar disorder. Conversely, patients with bipolar disorder might smoke more (often) as a result of the psychiatric disorder.

AIMS:

We conducted a bidirectional Mendelian randomisation (MR) study to investigate the direction and evidence for a causal nature of the relationship between smoking and bipolar disorder.

METHOD:

We used publicly available summary statistics from genome-wide association studies on bipolar disorder, smoking initiation, smoking heaviness, smoking cessation and lifetime smoking (i.e. a compound measure of heaviness, duration and cessation). We applied analytical methods with different, orthogonal assumptions to triangulate results, including inverse-variance weighted (IVW), MR-Egger, MR-Egger SIMEX, weighted-median, weighted-mode and Steiger-filtered analyses.

RESULTS:

Across different methods of MR, consistent evidence was found for a positive effect of smoking on the odds of bipolar disorder (smoking initiation ORIVW = 1.46, 95% CI 1.28-1.66, P = 1.44 × 10-8, lifetime smoking ORIVW = 1.72, 95% CI 1.29-2.28, P = 1.8 × 10-4). The MR analyses of the effect of liability to bipolar disorder on smoking provided no clear evidence of a strong causal effect (smoking heaviness betaIVW = 0.028, 95% CI 0.003-0.053, P = 2.9 × 10-2).

CONCLUSIONS:

These findings suggest that smoking initiation and lifetime smoking are likely to be a causal risk factor for developing bipolar disorder. We found some evidence that liability to bipolar disorder increased smoking heaviness. Given that smoking is a modifiable risk factor, these findings further support investment into smoking prevention and treatment in order to reduce mental health problems in future generations.

• Authors: Jentien M Vermeulen, Robyn E Wootton, Jorien L Treur, Hannah M Sallis, Hannah J Jones, Stanley Zammit, Wim van den Brink, Guy M Goodwin, Lieuwe de Haan, Marcus R Munafò
• Journal: The British journal of psychiatry : the journal of mental science (Br J Psychiatry) Vol. 218 Issue 2 Pg. 88-94 (02 2021) ISSN: 1472-1465 [Electronic] England
• PMID: 31526406 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Topics

• Bipolar Disorder (etiology, genetics)
• Genome-Wide Association Study
• Humans
• Mendelian Randomization Analysis
• Polymorphism, Single Nucleotide
• Smoking
• Smoking Cessation