Suboptimal Vitamin D Levels as a Peripheral Biomarker for Suicide Outcomes: Analysis of the UK Biobank Cohort

Suicide is a major global public health concern, with higher rates at higher latitudes. Vitamin D, a neuroactive steroid synthesized through sunlight exposure, has immunomodulatory effects and may influence neuroinflammatory pathways implicated in suicidal ideation and behaviour. We analysed UK Biobank data from participants who completed the 2016 (N=156,070) and 2022 (N=168,632) mental health questionnaires and had serum vitamin D levels and suicide outcomes data. Multinomial logistic regression examined associations between vitamin D and passive suicidal ideation, self-harm ideation, self-harm behaviour, and suicide attempt, adjusting for covariates. Suboptimal vitamin D levels were associated with increased risk across all outcomes. The strongest associations were observed for suicide attempt among deficient individuals (relative risk ratios [95% confidence intervals]: 1.25[1.08-1.44] and 1.30[1.13-1.49] in MHQ1 and MHQ2). Associations were present in both sexes, stronger in males, and persisted after excluding severe mental illness. These findings suggest potential public health relevance for suicide prevention.