Serum 25(OH)D levels significantly increased after treatment in TAK patients, and an increase of ≥ 8.45 µg/L was predictive of disease remission, especially in individuals with normal baseline ESR and/or CRP levels. Key Points • Following treatment, there was a significant increase in serum 25(OH)D levels among TAK patients. • The elevated changes in 25(OH)D levels before and after treatment demonstrated a positive correlation with the reduction in disease activity scores. • In patients with TAK before and after treatment, an elevation in serum 25(OH)D levels exceeding 8.45 µg/L serves as an indicator for disease remission, particularly prominent in individuals with normal baseline ESR and/or CRP levels.