Low Vitamin D Levels Found in Irish Women Diagnosed With Breast Cancer

Low Vitamin D Levels Found in Irish Women Diagnosed With Breast Cancer

A small study found that more than half of Irish women being treated with chemotherapy for breast cancer had lower-than-recommended levels of vitamin D.
Oct 14, 2019.

A small study found that many Irish women being treated with chemotherapy for early-stage breast cancer had levels of vitamin D that were lower than recommended.

The research was presented on Sept. 29, 2019, at the European Society for Medical Oncology 2019 Congress. Read the abstract of “Prevalence of vitamin D3 deficiency among women with early breast cancer receiving chemotherapy in an oncology dayward.


Vitamin D and breast cancer

Vitamin D, also known as vitamin D3, helps the body absorb the calcium that is essential for good bone health.

Studies looking at links between low vitamin D levels and cancer, including breast cancer, have offered mixed results. Still, we do know that vitamin D deficiency is common in women being treated for breast cancer, and some research suggests that low vitamin D levels increase the risk of breast cancer or the risk of breast cancer growing.


About the study

The Irish Longitudinal Study on Ageing estimated that 13.1% of the Irish population has lower-than-recommended vitamin D levels, compared to less than 6% of the U.S. population. So the researchers who did this study wanted to see how common low vitamin D levels were in women being treated with chemotherapy for early-stage breast cancer in one chemotherapy center.

To do the study, the researchers looked at the records of women being treated with chemotherapy to find women who had recorded vitamin D levels before they started chemotherapy. Overall, 41 women were included in the study.

The researchers defined lower-than-recommended vitamin D levels as less than 50 nmol/L (nanomoles/liter).

Before chemotherapy started, 66% of the women were considered to have lower-than-recommended vitamin D levels. The researchers also noted that the women’s vitamin D levels varied by season:

  • 88% of the women had lower-than-recommended vitamin D levels in the winter months

  • 0% of the women had lower-than-recommended vitamin D levels in the summer months

Women who had low levels of vitamin D tended to be:

  • younger

  • diagnosed with a higher-stage cancer

“We know from a national study that 13% of the Irish population are vitamin D deficient, but we found a much higher rate of deficiency — 66% — in our women with early-stage breast cancer starting chemotherapy in the dayward,” said Conleth Murphy, M.D., oncologist at Bon Secours Cork Cancer Center in Ireland, who presented the research. “We saw a marked seasonal variance. We don’t know whether this is causal, meaning women with vitamin D deficiency are more at risk of breast cancer, or an effect of the breast cancer diagnosis. I don’t start vitamin D replacement until women are finished their chemotherapy however, in case of a potential negative interaction.”


What this means for you

While the results of this study are interesting, more research is needed before vitamin D supplements routinely become part of breast cancer treatment. It’s very important to talk to your doctor before you start taking any vitamin D supplements. Taking too much vitamin D can be harmful. Vitamin D supplements should be taken only when your vitamin D levels are too low based on blood work done by a medical professional.

You might want to ask your doctor about the results of this study and whether checking your vitamin D levels makes sense for your unique situation. If your vitamin D level is low, you and your doctor can decide whether a vitamin D supplement is right for you. You also can ask your doctor about getting more direct sunlight exposure. Even short periods of direct peak sun exposure — 15 minutes three 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. Still, while sun exposure offers vitamin D benefits, it does have risks. Sun exposure can increase your risk of skin cancer, including melanoma, the most dangerous type.

For more information on vitamin D levels and how they can affect breast cancer, visit the Low Vitamin D Levels page in the Breastcancer.org Lower Your Risk section.

Written by: Jamie DePolo, senior editor

— Last updated on September 15, 2022, 7:39 PM

Reviewed by 1 medical adviser
Brian Wojciechowski, MD
Crozer Health System, Philadelphia area, PA
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