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Breast Cancer Health Center

Low Vitamin D Levels Common in Breast Cancer

Researchers Suggest Women With Breast Cancer Be Tested, Given Vitamin D Supplements if Needed
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WebMD Health News
Reviewed by Louise Chang, MD

Dec. 14, 2010 (San Antonio) -- More than half of women with breast cancer have low vitamin D levels, British researchers report.

"Women with breast cancer should be tested for vitamin D levels and offered supplements, if necessary," says researcher Sonia Li, MD, of the Mount Vernon Cancer Centre in Middlesex, England. The findings were presented at the San Antonio Breast Cancer Symposium.

Some studies have suggested a link between low vitamin levels and breast cancer risk and progression, but others have not, she says. No studies have proven cause and effect.

Previous research suggests a biologic rationale for vitamin D putting the brakes on breast cancer development and spread, Li says.

Breast cancer cells have vitamin D receptors, and when these receptors are activated by vitamin D, it triggers a series of molecular changes that can slow cell growth and cause cells to die, she says.

Even if it does not have a direct effect on the tumor, vitamin D is needed to maintain the bone health of women with breast cancer, Li says. That's especially important given the increasing use of aromatase inhibitors, which carry an increased risk of bone fractures, she says.

Vitamin D is found in some foods, especially milk and fortified cereals, and is made by the body after exposure to sunlight. It is necessary for bone health.

More Than 50% of Women Tested Have Low Vitamin D Levels

For the study, Li and colleagues collected blood samples from 166 women with breast cancer and measured their levels of vitamin D.

Of the total, 46% had vitamin D insufficiency, defined as levels between 12.5 and 50 nanomoles per liter (nmol/L) of blood. Another 6% had vitamin D deficiency, with levels lower than 12.5 nmol/L.

When ethnicity was considered, vitamin D levels were lower in Asian women than in white or other women: an average of about 36 nmol/L vs. 61 nmol/L and 39 nmol/L, respectively.

The researchers theorized that vitamin D levels would be higher in the summer, when there are more daylight hours, but the study showed no association between vitamin D levels and seasons.

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