Vitamin D Levels May Be Reason Some Women Benefit from Zometa Added to Chemo

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Zometa (chemical name: zoledronic acid) is used to strengthen bones and lower the risk of breaking a bone and other bone complications in women diagnosed with metastatic breast cancer that has spread to the bones.

Earlier research suggested that Zometa also might help stop breast cancer from spreading to the bones by making it harder for breast cancer cells to grow in bones and might help reduce the risk of the cancer coming back (recurrence) in women diagnosed with early-stage breast cancer.

New results from a large study suggest that postmenopausal women diagnosed with early-stage breast cancer who had adequate vitamin D levels got more benefits from Zometa combined with chemotherapy than women who had low vitamin D levels.

The research was presented at the 2012 San Antonio Breast Cancer Symposium.

The AZURE trial (Adjuvant Zoledronic Acid to Reduce Recurrence) included more than 3,355 women diagnosed with stage II or stage III hormone-receptor-positive breast cancer. The women were both pre- and postmenopausal. After surgery, all the women were treated with hormonal therapy and/or chemotherapy to reduce the risk of recurrence. Half the women were randomly assigned to also get Zometa; the other half didn’t get Zometa.

Overall, women who got Zometa were just as likely to have a recurrence as women who didn’t get Zometa. But when the researchers looked only at postmenopausal women, they found that postmenopausal women who got Zometa were less likely to have the cancer recur in the bones or other place away from the breast. This difference was significant, which means that it was probably because of the Zometa and not just due to chance. They wanted to know why.

Vitamin D helps the body absorb calcium, which is essential for good bone health. Vitamin D also helps the immune, muscle, and nervous systems function properly. Research suggests that women with low levels of vitamin D have a higher risk of breast cancer. Vitamin D may play a role in controlling normal breast cell growth and may be able to stop breast cancer cells from growing.

So the researchers analyzed the vitamin D levels in stored blood samples given by 872 women in the study before they started treatment:

  • 606 of the blood samples were from postmenopausal women
  • 266 of the blood samples were from premenopausal women

They found that only about 10% of the women had adequate vitamin D levels.

By comparing vitamin D levels to recurrence information, the researchers found:

  • low vitamin D levels were linked to recurrence in bones; this association was significant, which means that it was likely due to the low vitamin D levels and not just to chance
  • low vitamin D levels also were linked to the cancer recurring someplace in the body away from the breast, but this association wasn’t significant, which means it could have been due to chance

The women in the AZURE trial were given vitamin D supplements when the study started, but the supplements were 10 times lower than current recommended levels.

Right now, it’s not clear how or why vitamin D levels affect breast cancer spread. It may be that adequate vitamin D levels affect how breast cancer behaves; so when vitamin D levels are low, breast cancer is more likely to develop and if it does develop, it's more aggressive, harder to treat, and more likely to spread. It's also possible that low vitamin D levels are caused by other factors such as diet, exercise, and lifestyle choices that also affect breast cancer risk and prognosis.

Getting enough vitamin D, as well as calcium, is important for your overall good health -- especially the health of your bones. This study and other research suggest that getting enough vitamin D also might be important if you're being treated for breast cancer. Still, more research is needed to better understand the link between vitamin D and breast cancer. Checking vitamin D levels as part of routine healthcare might make sense. Still, it’s important to know that taking too much vitamin D can be harmful. Vitamin D supplements should be taken only when a blood test shows your vitamin D level is low.

Getting more direct sunlight exposure can also help boost your vitamin D levels. Even short periods of direct peak sun exposure – 15 minutes 3 times a week, for example – can give you more than the recommended daily amount of vitamin D. It’s also impossible to overdose on vitamin D from the sun. While sun exposure offers vitamin D benefits, it does have risks. Sun exposure increases your risk of skin cancer, including melanoma, the most dangerous type. In general, most experts recommend you continue to use sun protection when ultraviolet (UV) radiation levels are moderate or high.

If you're being treated for breast cancer, you might want to talk to your doctor about the results of this study. Ask if checking your vitamin D level makes sense for you. If it's low, you and your doctor can decide if a vitamin D supplement is right for you.

For more information on vitamin D, including the most reliable ways to ensure you have adequate vitamin D levels, visit the Low Vitamin D Levels page in the Breastcancer.org Lower Your Risk section.

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