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The study: Researchers looked at the connection between vitamin D levels at the time of breast cancer diagnosis and the occurrence of metastases (areas where the cancer has spread) and survival in 512 women diagnosed with breast cancer between 1989 and 1995. These women were followed for more than 11 years after diagnosis. Vitamin D is found in food and supplements and is made by the body after exposure to ultraviolet rays from the sun. It is necessary for bone health, and some studies have suggested that it may have a protective effect against breast cancer development.
The results: Only a small number of women (24%) had adequate levels of vitamin D when diagnosed with breast cancer. Women with low vitamin D levels at the time of diagnosis were more likely to have aggressive breast cancer (cancer that has a higher risk of spreading). Although these women were more likely to have breast cancer metastases and more likely to die from breast cancer when compared with women with adequate levels of vitamin D, more than two-thirds (69%) of these women did not have breast cancer metastases, and about three-fourths (74%) were still alive after 10 years. After 10 years, cancer did not spread in 83% of women with adequate vitamin D levels and 85% were still alive.
What this means for patients
“This study shows an association between low vitamin D levels and aggressive breast cancer, but we can't say at this time if very low vitamin D levels cause more aggressive cancer or if another factor is causing this association,” said lead author Pamela Goodwin, MD, Professor of Medicine at the University of Toronto, Canada, and holder of the Marvelle Koffler Chair in Breast Research at the Samuel Lunenfeld Research Institute, Mount Sinai Hospital. Dr. Goodwin also expressed concern that vitamin D deficiency was so common for women diagnosed with breast cancer. More studies are needed before any recommendations can be made about the possible breast cancer benefits of vitamin D supplements for women.
What to ask your doctor
- What is the evidence that nutrition affects my risk of breast cancer?
- What changes, if any, should I make to my eating habits? Are there vitamins or supplements I should avoid?
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