Scientists discover strange link between vitamin D and pain

The findings suggest that breast cancer patients with vitamin D deficiency (below 30 nmol/L) might benefit from taking vitamin D supplements before undergoing a radical mastectomy.

Researchers say growing evidence points to vitamin D playing an important role in how the body senses and regulates pain. Scientists believe this may be connected to the vitamin's anti inflammatory properties and its effects on the immune system. Vitamin D deficiency is also frequently seen in people with breast cancer.

Study Examined Pain After Breast Cancer Surgery

To explore the connection, researchers carried out a prospective observational study at Fayoum University Hospital in Egypt between September 2024 and April 2025.

The study included 184 women with breast cancer who were preparing to have surgery to remove one breast. Half of the participants had vitamin D deficiency (below 30 nmol/L), while the other half had vitamin D levels above 30 nmol/L. The two groups were otherwise similar, with average ages of 44 and 42.

Doctors and nurses caring for the patients did not know their vitamin D status. All participants received the hospital's standard treatment before, during, and after surgery.

During the operation, patients were given fentanyl to control acute pain. After surgery, everyone received intravenous paracetamol every eight hours. Patients were also able to self administer tramadol, another opioid pain medication, by pressing a control button.

Patients With Low Vitamin D Needed More Opioids

Pain levels were recorded immediately after surgery and again at 6, 12, 18, and 24 hours later. Researchers also tracked nausea, vomiting, sedation levels, and length of hospital stay.

Patients with vitamin D deficiency were three times more likely to experience moderate to severe pain during the first 24 hours after surgery compared with patients who had adequate vitamin D levels.

Researchers noted that none of the patients in either group reported severe pain of 7 or higher on the standard 0 to 10 pain scale. The difference was entirely related to a higher number of patients experiencing moderate pain levels between 4 and 6.

The vitamin D deficient group also required more opioid medication. On average, these patients received 8 μg more fentanyl during surgery, which researchers described as a modest increase.

However, after surgery, the difference became much larger. Patients with low vitamin D used an average of 112mg more tramadol than those with sufficient vitamin D levels. The medication was patient controlled, with doses capped at 50mg per hour.

Vitamin D and Recovery Complications

Opioid medications can lead to side effects such as nausea, vomiting, drowsiness, and confusion. They also carry risks of dependence and addiction.

The study found postoperative nausea occurred more often among patients with vitamin D deficiency. Vomiting was only reported in the deficient group, although researchers said the difference was too small to be considered statistically significant.

The researchers acknowledged several limitations. Because the study was observational and conducted at a single medical center, it cannot prove that low vitamin D directly caused the increase in pain. The team also did not measure inflammatory markers that might explain how vitamin D influences pain. In addition, information about anxiety, depression, cancer stage, previous treatments, and sleep problems before surgery was not collected.

Even with those limitations, the researchers concluded, "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."

They added, "Preoperative vitamin D supplementation in breast cancer patients with vitamin D levels below 30 nmol/L may have a role in modulating postoperative pain."