More than three decades later, Zhang's base of operations has moved to UCLA's School of Public Health. More than just time and distance separate what he does today from what he was doing 30 years ago. But his primary 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 where the incidence of mortality from stomach cancer is highest - on the small island of Yangzhong, China, situated on the Yangtze River in Jiangsu Province. After adjusting for age, gender, education, body mass index, and levels of smoking and alcohol consumption, green tea drinkers had a 48% lower risk of stomach cancer than non-drinkers, and a 51% lower risk of chronic gastritis.
"Green tea seems to have several important anti-cancer properties," Zhang says. "All tea comes from the same plant - Camellia sinensis. Certain chemicals in that plant, known as polyphenols, appear to have antioxidative activities." (Zhang notes that black tea loses many of its polyphenols in the fermentation process.)
The results of the study set Zhang and colleagues on a hunt for so-called tumor markers - early genetic changes that would foreshadow cancer development. Understanding these molecular changes would help researchers intervene at a more curable stage, or before malignancy ever takes hold.
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 another two years toward his Ph.D., all at Shanghai.
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 has been on the UCLA School of Public Health faculty since 1997.
"Using this new genetic knowledge for public health and environmental health science is very important," he says. "We're interested in using molecular genetics to prevent the disease.
"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."