Is vitamin D powerful enough to go head-to-head with cancer?

Yes, according to a growing body of evidence. High levels of vitamin D have been found to protect against several kinds of cancer, particularly those of the digestive system: mouth, throat, stomach, and colon. While many of us think we get plenty of vitamin D from milk or a multivitamin, it turns out that the best source is the sun. Its rays trigger your body to produce the nutrient, and a 10-20 minute stroll each day yields an abundant dose.

The resulting cancer protection is impressive. Study participants with high vitamin D levels had 43 percent fewer digestive-tract cancers, 29 percent fewer cancer deaths, and 17 percent fewer cancers overall. Although vitamin D is readily found in salmon, mackerel, herring, tuna, and sardines, as well as fortified milk and supplements, sun exposure won hands-down as the best source, because just a little light produces so much D.

How much of the sunshine vitamin do you need? About 1,500 IU each day to reap the protective rewards seen in the study, which is about how much a daily 10-20 minute walk produces. By contrast, a glass of milk has only 100 IU of D, and 3.5 ounces of salmon has 360 IU. Even the recommended daily dose is comparatively low: just 400-600 IU. But many public health experts are calling for the recommendation to be raised to 1,000-2,000 IU, the current upper limit considered safe for adults.

To get your daily dose of sun while minimizing skin risks -- you don't want to trade one cancer for another -- walk in the morning or afternoon, when the rays are less intense. And try applying a sunscreen just before you leave the house. Because it takes about 15-30 minutes for chemical sunscreens to kick in, by the time it starts working, you'll have gotten your daily D.