Background: Vitamin D has been extensively studied for its role in immune modulation, especially in the process of tolerance induction. The loss of tolerance towards self-antigens is the basis of several autoimmune disorders, this seems to be related to lower levels of Vitamin D. A neurological autoimmune disorder due to the loss of tolerance to compounds at the neuromuscular junction is known as Myasthenia Gravis (MG). Objective: To assess the possible correlation between altered Vitamin D levels and MG. Methods: In this systematic review, all recruited studies compared Vitamin D levels in MG patients and healthy controls. Five studies fulfilled selection criteria and were included for the quantitative synthesis. Methods: The meta-analysis involved data of a total population size of 450 individuals, quite equally divided in 219 cases and 231 controls, respectively. Results: The results showed a statistically significant mean difference between cases and controls. The overall mean Vitamin D levels in MG patients were 4.69 ng/ml lower than control levels (95%CI -6.17; -3.22), by applying a random-effects model this mean difference was estimated at -3.79 (95%CI -7.24; -0.33), after exclusion of data source of heterogeneity and through applying a fixed-effect model, resulted in a mean difference -5.39 (95%CI -6.91; -3.88). The p-value was lower than 0.05. Conclusion: Based on the current data, there are statically significant lower levels of Vitamin D in MG patients, so routine checking and possible correction should be advised in MG patients.

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