Vitamin D deficiency is associated with dry eye syndrome: a systematic review and meta‐analysis

A systematic review and meta‐analysis was conducted to determine the association between the serum vitamin D level and dry eye. A systematic literature search was performed using the PubMed, Embase, Web of Science and Cochrane Library databases to identify clinical studies evaluating the association between vitamin D levels and dry eye. The random‐effect model was used to combine the results. Possible sources of heterogeneity across studies were determined by meta‐regression and sensitivity analysis. Overall, 10 studies ( n  = 18 919) were included. Patients with dry eye had a mean serum vitamin D level that was lower than that in healthy controls by 3.99 ng/ml (95% CI −6.57, −1.40; p = 0.002). The mean Ocular Surface Disease Index score was higher (mean difference 10.70, 95% CI 1.55–19.86; p = 0.02) and Schirmer’s test without anaesthesia result was lower (mean difference 6.38 mm/5 min, 95% CI −10.48, −2.28; p = 0.002) in patients with vitamin D deficiency than in controls. Tear break‐up time was comparable in the vitamin D deficiency and control groups (p = 0.15). Sensitivity analyses indicated that the results obtained were robust. This meta‐analysis suggested that vitamin D deficiency is associated with worse subjective symptoms and less tear production in patients with dry eye. Vitamin D deficiency may be a risk factor for dry eye syndrome. Prospective cohort and intervention studies are warranted to determine if vitamin D has a protective role in the development of dry eye.