Patients who went into a mastectomy with low vitamin D were three times more likely to report moderate-to-severe pain in the first 24 hours after surgery, and they needed considerably more opioid medication. The finding comes from a prospective observational study of 184 women published on May 19, 2026 in the journal Regional Anesthesia and Pain Medicine.
The gap showed up most clearly at the 12-hour mark. Among vitamin D deficient patients, 17.4% had moderate-to-severe pain, compared with 2.2% of those with sufficient levels. Across the full 24 hours, the deficient group used about 112 mg more tramadol and received roughly 8 micrograms more fentanyl during surgery.
One important nuance sits behind the headline number. No patient in either group reported severe pain (7 or higher on a 0-10 scale). The three-fold difference was driven entirely by a higher share of moderate pain, in the 4 to 6 range, among those low in vitamin D.
How vitamin D may shape post-surgical pain
Surgery is a controlled form of injury, and the body's inflammatory response to that injury is a major driver of how much pain a patient feels. Researchers point to vitamin D's role in tempering that response. In the BMJ Group release, the authors describe the mechanism through vitamin D's anti-inflammatory effects and action on the immune system, both of which shape how tissue damage translates into pain.
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That biology is plausible, but the current study cannot prove it. The team acknowledged they did not measure inflammatory markers in the blood, so the proposed pathway is inferred rather than shown.
What the study can and cannot tell you
The research was carried out at Fayoum University Hospital in Egypt between September 2024 and April 2025. All 184 participants were women undergoing the same operation, a unilateral modified radical mastectomy, and were split into two groups of 92 based on whether their pre-surgery vitamin D level fell below or above 30 nmol/L, the threshold used by the NIH Office of Dietary Supplements to define deficiency.
Because the study observed patients rather than assigning them a treatment, it cannot establish that vitamin D deficiency caused the extra pain. It was also a single site, one surgery type, and did not collect data on anxiety, depression, cancer stage, prior treatment or pre-surgery sleep, all of which can influence how pain is felt.
Vitamin D deficiency is common in the United States. The NIH ODS estimates that about 1 in 4 adults have levels considered too low for bone and overall health, with older adults, people with darker skin, and those with obesity at higher risk.
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The practical takeaway is modest but concrete. If you have surgery on the calendar, especially a major operation, it is reasonable to ask your doctor whether a 25-hydroxyvitamin D blood test makes sense and whether supplementation is warranted before the procedure. Any decision to start, stop or dose a supplement should be made with a clinician who knows your medical history.
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