Loneliness and depression: bidirectional mendelian randomization analyses using data from three large genome-wide...

Area of Science:

• Psychiatry
• Genetics
• Epidemiology

Background:

• Major depression (MD) affects nearly 5% of the global population, with loneliness identified as a potential risk factor.
• Correlational studies suggest a link between loneliness and MD, but causal relationships remain unclear due to potential confounding factors.

Approach:

• This study employed Mendelian Randomization (MR) to investigate the causal associations between loneliness and MD.
• Utilized summary statistics from large genome-wide association studies (GWAS) for loneliness and MD from multiple cohorts, including the Psychiatric Genomics Consortium (PGC) and Million Veteran Program (MVP).
• Performed bidirectional analyses, assessing loneliness as a predictor of MD and MD risk variants as predictors of loneliness, using UK Biobank data for loneliness outcomes.

Key Points:

• Robust evidence supports a bidirectional causal relationship between loneliness and major depression.
• The causal link was observed for both depression case status and continuous measures of depressive symptoms.
• Results remained significant across sensitivity analyses, including those accounting for horizontal pleiotropy.

Conclusions:

• This research provides the first genetically-informed evidence that reducing loneliness may causally decrease the risk of developing depressive illness.
• Findings underscore the public health importance of loneliness reduction strategies for preventing or ameliorating major depression, particularly relevant in the context of the SARS-CoV-2 pandemic.