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Does vitamin D fight cancer?

    • Vitamin D helps prevent cancer cells from growing and spreading, a study says
    • Rates of breast and colon cancers tended to fall as average vitamin D levels rose
    • The U.S. government recommends 5 to 10 micrograms of vitamin D daily
  • Bottom Line: There's a growing body of evidence that vitamin D is good for fighting cancer, but studies are not sufficient to make a recommendation
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The American Cancer Society says best way to get vitamin D is from food and a daily supplement.

The American Cancer Society says best way to get vitamin D is from food and a daily supplement.

Overview

Researchers at the University of California, San Diego found that vitamin D intake is correlated with decreased rates of breast and colon cancers in 15 countries. The American Cancer Society says further study is needed. The study was published in January 2008 in the Journal of Steroid Biochemistry and Molecular Biology.

Questions and answers

What did the study find?

Dr. Sanjay Gupta, chief medical correspondent: Research has shown that vitamin D helps prevent cancer cells from growing and spreading, and some clinical trials have shown people given high doses of vitamin D had lower cancer risks. In this new study, researchers at the University of California, San Diego used data on average wintertime blood levels of vitamin D and rates of breast and colon cancers in 15 countries. They found that rates of the diseases tended to fall as average vitamin D levels went up.

People who live above 37 degrees latitude are considered especially at risk. This includes the northern U.S. and Canada because vitamin D levels in the winter are not enough. Study authors say, judging from their data, if Americans were able to maintain vitamin D levels, 60,000 cases of colon cancer and 85,000 cases of breast cancer could be prevented every year. Study authors recommended adults get 2,000 IU (international units) of vitamin D per day. That's about 50 micrograms -- which is the "tolerable upper intake level" set by the U.S. government. Do we all need to go out and get that much vitamin D? Well, probably not until further research proves as much.

What's the best way to get the right amount of vitamin D?

The government recommends 5 to 10 micrograms as an adequate amount of vitamin D for most people -- that's about two cups of milk for an average adult.

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The biggest source of vitamin D is sun exposure. Sunlight stimulates skin to make the vitamin. But this has its own set of problems with skin damage and skin cancer. A cup of vitamin D milk has about 2.5 micrograms. Other milk products such as yogurt and cheese are usually not fortified. So you have to put forth an effort to get enough vitamin D each day. The American Cancer Society says best way to get vitamin D is from food and a daily supplement, not the sun.

Can you get too much vitamin D? What are the risks?

You can get too much vitamin D and it leads to a buildup of calcium in the blood which can lead to kidney, heart and bone problems. Also there's such a thing as vitamin D toxicity, which can cause nausea, vomiting, poor appetite, constipation, weakness, and weight loss. So it's all about maintaining a balance. The American Cancer Society recommends talking to your doctor before adding any vitamin D supplements to what you actually need.

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Background
CNN spoke to Dr. Cedric Garland, D.P.H., adjunct professor of family and preventive medicine at the University of California, San Diego, about vitamin D. Below are excerpts from the interview.

CNN: Does the source of the vitamin D change how much you benefit in terms of lowering cancer risks?

Garland: It doesn't matter: supplements, food or sun or a combination of all.

CNN: What's a good amount of vitamin D to get?

Garland: The U.S. government recommends between 600 and 1000 IU.

CNN: How does color of your skin affect your vitamin D exposure?

Garland: For fair-skinned people, the researchers estimate that just three minutes in the sun can be adequate, while darker-skinned people may need about 15 minutes.

CNN: How much skin needs to be exposed?

Garland: No one is recommending that people bake in the sun to reach high vitamin D blood levels. Spending a matter of minutes in the midday sun, with 40 percent of the skin exposed, is enough.

CNN: How does location affect vitamin D exposure?

Garland: Above 37 degrees latitude seems to be the cutoff [where] wintertime levels of sun are not enough to provide enough vitamin D.

Read how to get vitamin D

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