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.