Causal links between socioeconomic status, leisure sedentary behaviours and gastro-oesophageal reflux disease: a multivariable two-sample Mendelian randomisation study.

Introduction: We implemented a two-sample multivariable Mendelian randomisation (MR) analyses to estimate the causal effect of socioeconomic status and leisure sedentary behaviours on gastro-oesophageal reflux disease (GERD).

Methods: Independent single-nucleotide polymorphisms associated with socioeconomic status and leisure sedentary behaviours at the genome-wide significance level from the Medical Research Council Integrative Epidemiology Unit (MRC-IEU) UK Biobank were selected as instrumental variables. Summary-level data for GERD were obtained from a recent publicly available genome-wide association involving 78 707 GERD cases and 288 734 controls of European descent. Univariable and multivariable two-sample MR analyses, using inverse variance weighted method for primary analyses, were performed to jointly evaluate the effect of socioeconomic status and leisure sedentary behaviours on GERD risk.

Results: Three socioeconomic status, including educational attainment (OR 0.46; 95% CI 0.30 to 0.69; p<0.001), average total household income before tax (OR 0.65; 95% CI 0.47 to 0.90; p=0.009) and Townsend Deprivation Index at recruitment (OR 1.60; 95% CI 1.06 to 2.41; p=0.026), were independently and predominately responsible for the genetic causal effect on GERD. In addition, one leisure sedentary behaviour, such as time spent watching television, was independently and predominately responsible for genetic causal effect on GERD (OR 3.74; 95% CI 2.89 to 4.84; p<0.001). No causal effects of social activities and driving on GERD were observed.

Conclusions: Genetically predicted Townsend Deprivation Index at recruitment and leisure watching television were causally associated with increased risk of GERD, and age at completion of full-time education and average total household income before tax were causally associated with decreased risk of GERD.