New research suggests that taking vitamin D, preferably D3, may prevent up to half of the cases of breast cancer and two-thirds of the cases of colorectal cancer in the United States. Vitamin D3 is produced by your body when your skin is exposed to sunlight. (You can also get it from fatty fish, egg yolks, fortified milk and other products, and supplements. D3 supplements are usually produced from lanolin, so vegans will prefer D2.) This doesn't mean you should stop wearing sunscreen entirely - white people exposed to summer sunlight in a bathing suit will produce all the vitamin D they need in only 15 to 20 minutes, while darker-skinned people will need longer exposures (which might explain why black men have a higher incidence of prostate cancer). Health Canada now recommends all adults over the age of 50 take a daily vitamin D supplement of 10 micrograms (400 IU), and, because "vitamin D synthesis in the skin is absent during the winter months (October to March)," they note that Canadians (and, one assumes, other people in northern climates) must rely on dietary intake of vitamin D to maintain adequate levels of vitamin D in the body.