Association of vitamin D deficiency with incident depression in patients with hearing impairment: an observational retrospective cohort study

Background Hearing impairment is associated with an elevated risk of depression, yet modifiable risk factors in this population remain poorly characterized. Although vitamin D deficiency (VDD) has been linked to depression in general populations, no large-scale study has examined this association among adults with hearing impairment. Methods This retrospective cohort study used the TriNetX Global Collaborative Network. Adults aged ≥18 years with hearing impairment who underwent serum 25-hydroxyvitamin D [25(OH)D] testing between 2010 and 2023 were classified into VDD (< 20 ng/ml) and sufficiency (≥30 ng/ml) cohorts. Thus, the study population represented a selected healthcare-utilizing cohort with available vitamin D measurements. After propensity score matching (48,184 per group), Cox models estimated hazard ratios (HRs) for incident depression over 12 years using a 1-year landmark design. Results For the primary outcome, VDD was associated with a significantly higher risk of overall depression ( HR , 1.57; 95% CI , 1.51–1.64; P < 0.001). For secondary outcomes, significant associations were observed for depressive episode ( HR , 1.60), recurrent depression ( HR , 1.62), suicidal behavior/self-harm ( HR , 1.47), and all-cause mortality ( HR , 1.40; all P < 0.001). The associations remained robust across sensitivity analyses ( HRs , 1.55–1.65). Subgroup analyses showed consistent associations across sex, age, and comorbidity strata, with significant effect modification by age, obesity, and chronic pain. Vitamin D insufficiency (20.0–29.9 ng/ml) showed a smaller but significant association ( HR , 1.37), consistent with an exposure-gradient pattern across predefined vitamin D categories. The negative control outcome (acute appendicitis) was non-significant ( P = 0.267). Conclusions VDD was associated with increased long-term depression risk among adults with hearing impairment who underwent serum 25(OH)D testing. Vitamin D status may represent a potential risk marker for depression in this selected healthcare-utilizing population; however, the observational design does not establish that vitamin D correction reduces depression risk.