Zuo-Feng Zhang was 16 when he arrived on the Nantong Farm one chilly spring day in 1969. His native China was in the midst of Mao Tse-tung's Cultural Revolution, and he had been sent to the countryside for "reeducation." He was then chosen by farmers as a "barefoot doctor." "The farmers would choose a student they trusted, then the student would go to a mid-level hospital for three months of training and come back as a doctor," he explained.

More than three decades later, Zhang is a professor in the School of Public Health and a member of the Jonsson Cancer Center. But his goal is still preventing disease, and as a cancer molecular epidemiologist, his work affects far more people.

A case in point is his recent finding -- publicized around the world -- that green tea has a protective effect against stomach cancer and chronic gastritis. Zhang conducted a population-based, case-control study on the small island of Yangzhong, China, where the incidence of mortality from stomach cancer is the highest in the world. He found that green tea drinkers had a 48% lower risk of stomach cancer than nondrinkers, and a 51% lower risk of chronic gastritis.

"Green tea seems to have several important anti-cancer properties," Zhang said. "All tea comes from the same plant -- Camellia sinensis. Certain chemicals in that plant, known as polyphenols, appear to have antioxidative activities."

The results of the study have set Zhang and colleagues on a hunt for so-called tumor markers -- early genetic changes that foreshadow cancer development.

Zhang was also lead author of a recent research article that reported that researchers from the Jonsson Cancer Center found, for the first time, that smoking marijuana may increase the risk of head and neck cancers.

How did a former barefoot doctor get to this point? After four years at Nantong Farm, Zhang earned a diploma in public health and then worked as an infectious-disease epidemiologist. In 1978 he began five years of medical school at Shanghai Medical University, followed by two years of an M.P.H. program in cancer epidemiology and two years toward his Ph.D.

Zhang came to the U.S. in 1988 and obtained his Ph.D. from the State University of New York at Buffalo in 1991. He arrived at UCLA in 1997.

"Prevention is what I've always done, even when I was a barefoot doctor. It's just that now the techniques look different, and my patients are entire populations."

-- Adapted from a story in Public Health magazine