Understanding Factors That Cause Tinnitus: A Mendelian Randomization Study in the UK Biobank

Objectives: To investigate the causal role of established risk factors and associated conditions to tinnitus and tinnitus severity in the UK Biobank. Design: The prospective cohort study with large dataset of >500,000 individuals. The analytical sample of 129,731 individuals in the UK Biobank of European descent. Participants were recruited from National Health Service registries, baseline age range between 37 and 73 years, response rate to baseline survey 6%. Participants were asked subjective questions about tinnitus and its severity. Previously observed associations (n = 23) were confirmed in the UK Biobank using logistic and ordinal regression models. Two-sample Mendelian randomization approaches were then used to test causal relationships between the 23 predictors and tinnitus and tinnitus severity. The main outcome measures were observational and genetic association between key demographics and determinants and two tinnitus outcomes (current tinnitus and tinnitus severity). Results: Prevalence of tinnitus was 20% and severe tinnitus 3.8%. The observational results are consistent with the previous literature, with hearing loss, older age, male gender, high BMI, higher deprivation, higher blood pressure, smoking history, as well as numerous comorbidities being associated with higher odds of current tinnitus. Mendelian randomization results showed causal correlations with tinnitus. Current tinnitus was predicted by genetically instrumented hearing loss (odds ratio [OR]: 8.65 [95% confidence interval (CI): 6.12 to 12.23]), major depression (OR: 1.26 [95% CI: 1.06 to 1.50]), neuroticism (OR: 1.48 [95% CI: 1.28 to 1.71]), and higher systolic blood pressure (OR: 1.01 [95% CI:1.00 to 1.02]). Lower odds of tinnitus were associated with longer duration in education (OR: 0.74 [95% CI: 0.63 to 0.88]), higher caffeine intake (OR: 0.89 [95% CI: 0.83 to 0.95]) and being a morning person (OR: 0.94 [95% CI: 0.90 to 0.98]). Tinnitus severity was predicted by a higher genetic liability to neuroticism (OR: 1.15 [95% CI: 1.06 to 1.26]) and schizophrenia (OR: 1.02 [95% CI: 1.00 to 1.04]). Conclusions: Tinnitus data from the UK Biobank confirm established associated factors in the literature. Genetic analysis determined causal relationships with several factors that expand the understanding of the etiology of tinnitus and can direct future pathways of clinical care and research.