Women with breast cancer often experience severe joint pain as a consequence of treatment with aromatase inhibitors like Tamoxifen. Researchers in Barcelona suggest that vitamin D supplementation can prevent or at least reduce the pain.

This is important because severe arthralgias often limit a woman’s willingness to complete tamoxifen treatment.

Daniel Prieto-Alhambra and colleagues at the Hospital del Mar, studied a cohort of 290 breast cancer patients undergoing treatment with Tamoxifen or another of the aromatase inhibitors (AIs). At baseline, 90% had serum vitamin D levels under 30 ng/ml, which is considered deficient in sunny Spain.

All the patients were given 800 IU/d vitamin D, but those who were deficient also got an additional 16,000 oral boost every two weeks.

Among the women who were pain-free at baseline, those who reached serum levels of 40 ng/ml were 50% less likely to experience drug-associated joint pain than those who remained vitamin D deficient.
The authors note, however, that it is challenging to get the blood levels up to this protective level. At 3 months, 50% of the women treated with the booster doses were still deficient (Prieto-Alhambra D, et al. Breast Ca Res Treat. 2010; DOI: 10.1007/s10549-010-1075-9)

“We conclude that most women requiring AI therapy have low concentrations of vitamin D at baseline, and the appearance of AI-induced arthralgias in women with early breast cancer is associated with their plasma concentrations of Vitamin D,” said Dr. Prieto-Alhambra.

The relationship between vitamin D, breast cancer, and aromatase inhibitors is complex. The Barcelona group had previously shown that vitamin D deficiency is extremely common in women treated with these drugs. The question is whether drugs like Tamoxifen can cause the deficiency.
There is some evidence that aromatase inhibitors compromise vitamin D metabolism by competing with cytochrome P3A4 enzymes in the liver. The clinical significance of this has not yet been determined.

Dr. Prieto-Alhambra and colleagues recommend routinely assessing serum vitamin D levels in any woman considering aromatase inhibitor therapy, and supplementing if she is deficient. Not only might the vitamin reduce the odds of drug-associated joint pain, it might actually reduce risk of recurrence.