Harvard Women's Health Watch

Higher vitamin D may help prevent breast cancer

It's probably time to revise official advice about how much is enough.

We've known for a long time that vitamin D is crucial to bone health. Research is now showing that it's active in many other tissues and may offer some protection against a range of diseases, including certain cancers. To get this benefit, though, we likely need more than the current recommended amounts.

At the American Association for Cancer Research meeting in April 2006, researchers offered compelling evidence that boosting vitamin D intake could help reduce the risk of breast cancer. In a study of 1,760 women, California scientists found that risk fell steadily with increasing blood levels of vitamin D. The highest levels (more than 52 nanograms per milliliter, or ng/mL) correlated with a 50% reduced risk of breast cancer, compared with the lowest amounts (less than 12 ng/mL). To reach a blood level of 52 ng/mL, you would need several times the recommended intake, which is 400 international units (IU) of vitamin D per day for women ages 50–70.

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