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Breast Cancer Health Center

Vitamin D Deficiency Worsens Breast Cancer?

Inadequate Levels of Vitamin D Linked to Sharply Increased Odds of Cancer Spread, Death
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Vitamin D Deficiency Linked to Poor Breast Cancer Prognosis

After 10 years, 83% of women with adequate levels were alive without signs of cancer spread (metastasis) vs. only 69% of women with vitamin D deficiency. Most of the deaths were from breast cancer.

For women with insufficient levels of vitamin D, there was a slightly increased risk of cancer spread compared to women with sufficient levels, but the difference was so small it could have been due to chance. "And their risk of death was the same," Goodwin says. "So the majority of the [negative] effect is in women with a deficiency."

But there was a point above which there seemed to be too much of a good thing, Goodwin says. If vitamin D blood levels were too high, the risk of dying appeared to rise, although the number of women with very high levels was so small that the finding could be due to chance.

"Our concern is that women may think, if some is good, more must be better, and increase vitamin D intake beyond what's optimal," she says.

So just what is optimal? A reading of 80 to 120 nanomoles per liter, according to Goodwin. That range has also been shown to be optimal for bone and heart health, she says.

Vitamin D Testing

If you don't know your vitamin D level, you're not alone: Doctors don't routinely order it as part of the blood tests taken for an annual physical, Goodwin says.

Julie Gralow, MD, chairwoman of ASCO's Cancer Communications Committee and associate professor of medicine at the University of Washington in Seattle, suggests that women with breast cancer take the initiative and ask about having their vitamin D levels measured.

"We now have a reliable test, and we know to safely correct deficiencies," she tells WebMD.

Goodwin says there is evidence to suggest that for women with a deficiency, taking 800 international units (IU) of vitamin D a day can raise levels to the optimal range.

For healthy people without a deficiency, current recommendations call for people between ages 0-50 to get 200 IU of vitamin D daily, with 400 IU recommended for those between the ages of 51 and 70. After age 70, 600 IU of vitamin D are recommended each day.

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