Association between preoperative vitamin D level and postoperative pain in patients undergoing breast cancer surgery: a prospective observational study

Background This study investigated the relationship between preoperative serum vitamin D levels and acute postoperative pain scores in patients undergoing unilateral breast cancer surgery. Methods The study was conducted at Fayoum University Hospital between September 2024 and April 2025. 184 American Society of Anesthesiologists (ASA) II–III female patients scheduled to undergo elective unilateral modified radical mastectomy were classified into two groups: 92 vitamin D-deficient (<30 nmol/L) and 92 vitamin D-sufficient (≥30 nmol/L). The primary outcome was the occurrence of moderate to severe postoperative pain (Numerical Rating Scale (NRS) >3) at 12 hours. A secondary 24-hour composite outcome (NRS >3 at any time within the first 24 hours) was used for the multivariable logistic regression. Other secondary outcomes included: preoperative serum 25(OH)D level, postoperative NRS, intraoperative fentanyl consumption, postoperative tramadol consumption, sedation scores, intraoperative and postoperative hemodynamics, patient satisfaction, and hospital stay. Results The baseline characteristics were well balanced between the groups, with small standardized mean differences for all variables. Patients with vitamin D deficiency had a higher occurrence of moderate to severe pain at 12 hours. In multivariable analysis, vitamin D deficiency was independently associated with moderate to severe postoperative pain at any time point during the first 24 hours (adjusted OR 3.12, 95% CI 1.58 to 6.13). Vitamin D-deficient patients had higher intraoperative fentanyl consumption (mean difference 8.04 µg, 95% CI 3.21 to 12.88) and postoperative tramadol consumption (mean difference 112.17 mg, 95% CI 101.44 to 122.91). Conclusion Vitamin D deficiency is associated with a higher occurrence of moderate to severe postoperative pain and increased opioid consumption in patients undergoing unilateral modified radical mastectomy.