Since sunlight is responsible for producing vitamin D in the human body, researchers have wondered if this could be the connection. Some test-tube studies have shown that vitamin D inhibits the growth of cancer cells, including those in the breast and prostate. Last year a research team at the Northern California Cancer Center analyzed statistics from a survey of a large group of American women and found that women with higher sun exposure and those with a high dietary intake of vitamin D had a lower risk of breast cancer. This was backed up by a study from the University of North Carolina at Chapel Hill. Any news that might help unravel cancer mysteries is welcome, but this is very preliminary research.
Some evidence also points to a link between vitamin D and reduced risk of colon cancer.
But all this does not mean you should move south or start sunbathing. Unique among the vitamins, vitamin D is a hormone, and like other hormones it is manufactured in the body. It helps the body utilize calcium and phosphorus and builds bones and teeth. Like many other nutrients, it probably has a beneficial effect on the immune system. You don't actually need to consume vitamin D, provided you get a minimal amount of sunlight, which causes your skin cells to manufacture the vitamin.