Breast cancer patients who were vitamin D deficient before a mastectomy were about three times as likely to report moderate to severe pain in the first 24 hours after surgery, and they used more opioid medication, according to a 184-patient study published online in May in Regional Anesthesia & Pain Medicine.
The study's design sets clear limits on what it can show. It was observational and conducted at a single hospital, so it cannot prove that low vitamin D caused patients to feel more pain or use more opioids. The researchers acknowledged that limitation.
For someone facing breast surgery, the practical takeaway is narrow. The findings raise a simple question to discuss before an operation. They do not justify starting high-dose supplements without medical advice.
Inside the Study Design and Findings
Researchers conducted the prospective observational study at Fayoum University Hospital in Egypt between September 2024 and April 2025, according to a press release from BMJ Group, which publishes the journal. The study was registered on ClinicalTrials.gov. It included 184 breast cancer patients scheduled to have one entire breast removed. Half had vitamin D levels below 30 nmol/L and were classified as deficient. The other half had levels above that cutoff and were classified as sufficient.
The two groups had similar characteristics. The average age was 44 in the deficient group and 42 in the sufficient group. The clinical staff caring for the patients did not know their vitamin D levels, which reduced the chance that this information affected pain treatment.
All patients received the opioid fentanyl during surgery and intravenous acetaminophen (called paracetamol outside the United States) every eight hours afterward. They could also give themselves doses of the opioid tramadol by pressing a button. Patients rated their pain right after surgery and again at 6, 12, 18, and 24 hours.
One detail helps explain the main finding. No patient in either group reported severe pain, defined as 7 or higher on a 0-to-10 scale. The difference between the groups came entirely from moderate pain, scored 4 to 6.
The difference in opioid use was clearer after surgery than during it. Patients in the deficient group received an average of 8 micrograms more fentanyl during surgery, a difference the researchers described as modest. After surgery, they used about 112 mg more tramadol. Nausea after surgery was more common in the deficient group, and vomiting occurred only in that group, although the difference in vomiting was small and not statistically significant.
The Gaps That Limit What This Means
Beyond the observational design, the authors noted important missing data. They did not measure inflammatory markers, so they could not explore how vitamin D might affect pain. They also did not collect information on anxiety, depression, cancer stage, cancer treatment, or sleep problems before surgery.
Those gaps matter because each of those factors can affect how much pain a person reports after surgery. Low vitamin D may also reflect other differences, such as sun exposure, body weight, diet, or chronic illness, and any of these could explain part of the pain difference.
The study's cutoff also needs context. A level below 30 nmol/L, or about 12 ng/mL in the units most U.S. labs use, is the threshold commonly used to define risk of deficiency. Levels from 30 to 49 nmol/L are generally considered at risk of inadequacy. That means the study's "sufficient" group likely included some people whom U.S. standards would consider low. Deficiency at this level is not common in the United States. A national analysis of U.S. survey data from 2011 to 2014 found that about 5% of people were at risk of deficiency.
The findings also come from one hospital in Egypt, where typical vitamin D levels and pain management practices may differ from those in U.S. hospitals.
The published paper concludes that vitamin D deficiency is associated with more moderate to severe pain and higher opioid use after this type of mastectomy. The authors suggest that vitamin D supplements before surgery may help reduce pain in patients with levels below 30 nmol/L. That idea still needs to be tested.
The Conversation Worth Having Before Surgery
The practical step is a conversation, not a supplement purchase. Anyone scheduled for a mastectomy or another major operation can ask the surgical team whether checking vitamin D makes sense and whether correcting a deficiency beforehand would be worthwhile.
There are good reasons to ask rather than self-treat. Vitamin D is stored in the body, and very high doses over time can raise blood calcium to dangerous levels. Correcting a deficiency also typically takes weeks, so starting a supplement just before surgery is unlikely to change vitamin D levels in time.
People who are more likely to have low vitamin D include those with darker skin or limited sun exposure, people with obesity, people with conditions that affect fat absorption such as celiac disease or inflammatory bowel disease, and people who have had gastric bypass surgery. Vitamin D deficiency is also commonly reported among patients with breast cancer, which helped prompt this research.
Pain planning is the more important part of the pre-surgery conversation. Patients can ask about regional nerve blocks, scheduled non-opioid pain relievers, and a clear plan for the first few days at home. These approaches are already part of standard pain management and do not depend on this study. Patients can also ask whether vitamin D testing would be covered in their case.
Anyone recovering from surgery whose pain is getting worse instead of better, or who develops fever, spreading redness, wound drainage, or sudden shortness of breath, should contact the surgical team promptly.
A randomized trial giving vitamin D to deficient patients before surgery and then measuring pain would be needed to answer the question. Until then, this is a reasonable topic to raise with a surgical team, not a reason to change treatment on your own. MedicalDaily has also reported on research linking vitamin D supplements to faster cognitive decline, another association that does not prove cause and effect.
Key Questions Answered
What did the study find? Patients with vitamin D levels below 30 nmol/L before mastectomy were about three times as likely to report moderate to severe pain in the first 24 hours and used about 112 mg more tramadol after surgery.
Does this prove vitamin D reduces pain? No. The study was observational and took place at one hospital, so it cannot establish cause and effect.
Was anyone in severe pain? No. No patient in either group scored 7 or higher on the 0-to-10 pain scale. The difference came entirely from moderate pain.
Should I start vitamin D before surgery? Ask your surgical team rather than self-treating. Vitamin D is stored in the body, and very high doses can raise calcium to dangerous levels.
Who is most likely to have low vitamin D? People with darker skin or limited sun exposure, obesity, conditions that affect fat absorption, or a history of gastric bypass surgery.
Has surgical guidance changed? No. This single study has not changed anesthesia or surgical guidelines.
What can help with pain after surgery? Ask your surgical team about regional nerve blocks, scheduled non-opioid pain relievers, and a clear plan for the first days at home.
