A new study has reported that vitamin D deficiency is common in postmenopausal breast cancer survivors using aromatase inhibitors, even among those taking vitamin D suplements. Aromatase inhibitors (including Arimidex, Aromasin and Femara) are a type of first-line hormonal treatment for postmenopausal estrogen receptor positive (ER+) breast cancer. Breast cancer patients treated with aromatase inhibitors are at risk for decreased bone density and fractures. Given that vitamin D plays an important role in bone metabolism, vitamin D deficiency may put these patients at an additional risk. The study included 391 postmenopausal women with stage I to III breast cancer undergoing aromatase inhibitor therapy.

Study participants had an average vitamin D level of 35 ng/mL; 35% of the women were found to be deficient, defined as having a level below 30 ng/mL. Most (73.4%) of the participants were taking vitamin D supplements (as documented in their medical charts), yet 26.8% of these women were still vitamin D deficient. Non-white patients were twice as likely to be vitamin D deficient, and overweight and obese women were approximately three times as likely to be deficient as normal weight women. When adjusting for vitamin D supplementation, the discrepancy between normal weight patients and obese patients became even more pronounced, suggesting that standard vitamin D supplementation may not be sufficient for these patients. The authors conclude that vitamin D deficiency is common among breast cancer survivors, and those who are non-white or have a body mass index (BMI) greater than 25 are at a higher risk of deficiency. In light of data linking vitamin D deficiency and bone health, oncologists should consider routine testing (with particular attention to non-white or overweight patients) and repleting those patients who are deficient.

Comments regarding the study

As the study authors suggest, breast cancer patients probably would benefit from having their vitamin D levels tested and working with their primary care physicians and oncologists to bring the level up to a more optimal level if a deficiency is found. Several studies have reported that women deficient in vitamin D may have a worse breast cancer prognosis than those who are not. Please see our article on vitamin D for an in depth discussion of the relationship between vitamin D and breast cancer.