Table 3. Summaries of studies on vitamin D and Bell's palsy and hemifacial spasm.

BP: Bell's palsy; HFS: Hemifacial spasm

Article	Study design	Study characteristics	Main findings
Uysal et al. [32]	Retrospective case-control study	Sample size = 102 containing 52 BP cases and 50 controls	Vitamin D deficiency in BP patients was lower compared to controls. Similarly, high-grade BP patients had lower vitamin D levels compared to low-grade BP patients
Ocak et al. [35]	Prospective case-control study	Sample size = 91 with 43 BP cases and 48 normal individuals	No significant difference in vitamin D between both groups; however, poor outcome was observed in vitamin D-deficient individuals.
Ulusoy [37]	Prospective case-control study	Sample size = 160 with 80 BP cases and 80 normal individuals	Low vitamin D levels in HFS compared to controls. But no effect of vitamin D on the severity of the disease