Abstract
There are few studies on risk factors for frozen shoulder, and even fewer Mendelian randomization (MR) studies on frozen shoulder. Therefore, we conducted a two-sample MR study to explore whether socioeconomic status (years of schooling, average total household income before tax), obesity (body mass index and waist circumference), individual behaviors (smoking initiation, alcohol intake frequency, coffee intake, nonoily fish intake, tea intake, beef intake, bread intake, cheese intake, oily fish intake, and fresh fruit intake), and diabetes (type 1 and type 2 diabetes) are associated with frozen shoulder. The exposure datasets and the outcome dataset were extracted from the MRC Integrative Epidemiology Unit at the University of Bristol Open genome-wide association studies project (https://gwas.mrcieu.ac.uk/). We conducted MR analyses using the inverse variance weighted (primary method), MR-Egger, and weighted median methods and conducted heterogeneity and pleiotropy analyses. Type 1 diabetes (OR: 1.103; 95% CI: 1.053-1.156; P = .0000410) was associated with an increased risk of frozen shoulder. Cheese intake (OR: 0.490; 95% CI: 0.267-0.899; P = .0213), non-oily fish intake (OR: 0.0993; 95% CI: 0.0220-0.448; P = .00267), years of schooling (OR: 0.453; 95% CI: 0.349-0.588; P = .00000000277), and average total household income before tax (OR: 0.434; 95% CI: 0.253-0.743; P = .00236) were discovered as protective factors. No horizontal pleiotropy was found in all analyzes we performed (P > .05). Our study indicated that type 1 diabetes was a risk factor for frozen shoulder while cheese intake, non-oily fish intake, years of schooling, and average total household income before tax were considered as protective factors for frozen shoulder.