Breast cancer surgery patients with low vitamin D levels reported more postoperative pain and used substantially more opioid painkillers in the first 24 hours after mastectomy than patients with sufficient levels, according to a study in Regional Anesthesia Pain Medicine. The research followed 184 patients at a single hospital in Egypt between September 2024 and April 2025, and offers a concrete, testable angle for surgical teams looking to reduce opioid exposure.
What the study measured
The prospective observational study enrolled 184 women scheduled for unilateral modified radical mastectomy at Fayoum University Hospital in Egypt. Half had preoperative vitamin D levels below 30 nmol/L, classified as deficient, and half had levels above that threshold. The deficient group’s average age was 44, compared with 42 in the sufficient group.
All patients received the same standardized care: fentanyl during surgery, intravenous paracetamol every eight hours after surgery, and patient-controlled tramadol with a maximum dose of 50 milligrams per hour. Clinical staff did not know each patient’s vitamin D status, which the study authors identified as a methodological strength because it limits bias in pain assessment and medication decisions.
Patients rated their pain on a 0-10 scale immediately after surgery and again at six-hour intervals through 24 hours. Researchers also tracked nausea, vomiting, sedation levels, and length of hospital stay.
The pain and opioid findings
Vitamin D deficient patients were three times more likely to report moderate to severe pain at any point during the first 24 hours compared with patients who had sufficient vitamin D. No patient in either group reported severe pain rated 7 or above, so the entire gap between groups came from moderate pain rated 4 to 6.
The opioid gap was larger. Patients in the deficient group received an average of 8 micrograms more fentanyl during surgery, a difference the study authors described as modest. After surgery, the same group used an average of 112 milligrams more tramadol than patients with sufficient vitamin D. Because patients controlled their own tramadol through a patient-controlled system, the researchers could measure exactly how much additional opioid each person required.
Postoperative nausea was more common among deficient patients, and vomiting occurred only in the deficient group, though the study noted the difference was small and not statistically significant. Greater opioid use matters in this setting because these drugs can cause nausea, vomiting, drowsiness, and confusion, and carry risks of dependency and addiction.
Why vitamin D status might matter for surgical pain
Vitamin D is best known for its role in bone health, but the study points to growing evidence that it may also influence how the body senses and processes pain. The mechanism may run through inflammation and immune function, both of which can shape pain responses. Other research has linked vitamin D deficiency to chronic pain conditions, including fibromyalgia. A separate study of more than 561,000 adults found that people with vitamin D levels below 20 ng/mL were 63% more likely to develop fibromyalgia than those with levels of 30 ng/mL or higher.
Vitamin D deficiency is frequently reported among people with breast cancer, which is part of why researchers are examining whether low levels might affect pain after surgery. A 2026 report found that 29% of U.S. adults are clinically deficient in vitamin D and another 42% have insufficient levels, a gap linked to indoor lifestyles that limit sun exposure. The nutrient can also be obtained through certain foods and supplements.
What the study cannot show
Because the study was observational and conducted at a single center, it cannot prove that vitamin D deficiency directly caused patients to experience more pain or use more opioids. The researchers did not measure inflammatory markers, so they could not investigate the biological mechanisms that might explain the link. The study also lacked data on factors that can influence postoperative pain, including anxiety, depression, cancer stage, cancer treatment, and sleep disturbance before surgery.
The authors concluded that preoperative vitamin D supplementation may have a role in modulating postoperative pain, but they stopped short of recommending routine supplementation for this purpose. Randomized controlled trials would be needed to test whether correcting deficiency before mastectomy actually reduces postoperative pain and opioid requirements.
What this means for surgical teams and patients
For clinicians, the study adds to a case for checking vitamin D status before major breast surgery. A simple blood test before the operating date could flag patients who may need more pain control and who might benefit from preoperative supplementation. For patients, the practical takeaway is that addressing a known deficiency in the weeks before surgery is a low-risk step that may pay off in less pain and fewer opioids during recovery.
FAQ
Does low vitamin D cause more pain after breast cancer surgery?
The study found an association, not a cause. Vitamin D deficient patients reported more moderate pain and used more tramadol after mastectomy, but the observational design cannot prove that low vitamin D directly caused the difference.
How much more opioid did deficient patients use?
Vitamin D deficient patients received an average of 8 micrograms more fentanyl during the operation and used an average of 112 milligrams more tramadol in the first 24 hours after surgery, compared with patients who had sufficient vitamin D.
Could vitamin D supplements reduce pain after mastectomy?
The study authors said preoperative vitamin D supplementation may have a role in postoperative pain, and called for randomized trials to test whether correcting deficiency before surgery actually lowers pain scores and opioid requirements.
