2.4. Intervention
At their first outpatient postoperative follow-up visit, patients who had been enrolled in the study were subjected to random assignment. They were instructed to take either the vitamin D3 supplement (2000 IU/day) or placebo orally daily, beginning on the same day, until the conclusion of the trial. Both the vitamin D3 supplements and placebos were procured from Zenyaku Pharmaceutical Co., Ltd., Tokyo, Japan.