Marin County, California has one of the highest rates of breast cancer in the world, a fact that scientists know has nothing to do with the land itself but with some other, unknown factor

A new study that analyzed mouth buccal cell samples stored frozen at the University of California, San Francisco (UCSF) suggests what this factor may be: a genetic trait present among women within the county's predominantly white population. Scientists found that, in a small, retrospective pilot study involving buccal cells from 338 women living in Marin, slight variations within the DNA of a human gene for vitamin D receptor were associated with breast cancer risk. Researchers found that women who were at high risk for breast cancer were 1.9 times more likely to have a specific vitamin D receptor variation than the general population.