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Disentangling the effects of nicotine versus non-nicotine constituents of tobacco smoke on major depressive disorder: A multivariable Mendelian randomisation study

  • 0School of Psychological Science, University of Bristol, Bristol, UK.
Addiction +

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February 11, 2025

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February 11, 2025

View abstract on PubMed

Summary

This summary is machine-generated.

Smoking heaviness, not nicotine, appears to be the primary driver of depression risk. This study used Mendelian randomization to analyze the causal link between smoking and depression, suggesting alternative pathways beyond nicotine exposure.

Area Of Science

  • Genetics
  • Psychiatry
  • Epidemiology

Background

  • Growing evidence links tobacco smoking to depression, but the specific causative agents remain unclear.
  • Investigating whether nicotine or other tobacco smoke constituents drive depression risk is crucial for public health.
  • Mendelian randomization (MR) offers a method to assess the independent effect of nicotine, adjusting for smoking heaviness.

Purpose Of The Study

  • To determine the independent causal effect of nicotine exposure on major depressive disorder (MDD) risk.
  • To differentiate the impact of nicotine metabolite ratio (NMR) from cigarettes per day (CPD) on MDD.
  • To explore alternative causal pathways between smoking and depression beyond nicotine.

Main Methods

  • Employed univariable and multivariable Mendelian randomization (MVMR) analyses.
  • Utilized genome-wide association study (GWAS) summary statistics for CPD (n=143,210) and NMR (n=5,185) in European ancestry individuals.
  • Analyzed individual-level MDD GWAS data from UK Biobank (n=35,871-194,881) using inverse variance weighted (IVW) regression.

Main Results

  • Univariable MR showed a causal effect of CPD on MDD (OR=1.13, P=0.003) but no clear effect of NMR (P=0.134).
  • MVMR confirmed a causal effect of CPD on MDD when accounting for NMR (IVW OR=1.19, P=0.017).
  • Weak evidence suggested a small effect of NMR on MDD when accounting for CPD (IVW OR=0.98, P=0.057).

Conclusions

  • The causal effect of smoking on depression risk appears largely independent of nicotine exposure.
  • Alternative causal pathways, not solely nicotine, likely contribute to the smoking-depression link.
  • While nicotine's role cannot be entirely dismissed, other tobacco constituents or mechanisms are more significant drivers.

Keywords:

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