TH and Parkinson disease: The brain substantia nigra in PD has a high level of expression of the VD metabolizing enzyme and 1α hydroxylase, and VD can stimulate the expression of tyrosine hydroxylase, a key enzyme of dopamine synthesis in PD, which affects the production and turnover of dopamine, therefore, the role of VD in the development process of PD has received increasing attention (85, 86).