The science of large numbers

Cohort studies shed light on cancer

Stephen Doster
Published: February, 2007

Every year, 50 modern-day gumshoes fan out across Shanghai, China, hot on the trail of some of the worst miscreants that afflict the human race.

Armed with survey forms, they question the inhabitants of thousands of homes. Their goal: to find out why some people develop cancer and other diseases, and others don’t.

Begun a decade ago by researchers now at Vanderbilt University Medical Center, the Shanghai Women’s Health Study has yielded important clues to the mysterious connections between environment, genetics and disease.

For example:

  • Women who have never smoked but whose husbands are heavy smokers are at greatly increased risk of dying from stroke.
  • High intake of soy foods lowers blood pressure and decreases the risk of both coronary heart disease and bone fractures.

“Sometimes the associations between lifestyle and disease are so striking it surprises us,” says Wei Zheng, who directs the Shanghai study with his wife and colleague, Xiao Ou Shu. “We are conducting additional studies to get more definitive answers.”

The Shanghai investigation is known as an epidemiological “cohort” study. It is designed to track the development of disease in a large group of people over an extended period of time—usually decades.

Cohort studies can help reveal the impact that diet, exercise and other lifestyle factors can have on health and longevity. More recently, they’ve been used to explore the disproportional impact of disease on different ethnic groups.

An example is the landmark Southern Community Cohort Study, which is attemptng to explain why African-Americans are more likely than other groups to develop and die from cancer.

The study is a collaboration of the Vanderbilt-Ingram Cancer Center, Meharry Medical College and the International Epidemiology Institute (IEI), a biomedical research firm based in Rockville, Md.

Since it was launched in 2001, about 63,000 adults aged 40 to 79 have been enrolled through community health centers in 12 Southeastern states, including Tennessee. The goal is to recruit 90,000 participants.

“Historically, the home of the African-American population in the United States has been in the South,” explains William Blot, Ph.D., IEI chief executive officer and the study’s principal investigator. “There had never been an investigation in the South on this order of magnitude.

“When you start getting up in numbers of people with a particular type of cancer that approaches 1,000, that gives you pretty good power to start looking at environmental and genetic factors,” says Blot, who also is a professor of Medicine at Vanderbilt.

Focus on the good

Zheng got the idea for the Shanghai Women’s Health Study in the early 1990s while working at the University of Minnesota.

He and his wife met at Shanghai Medical University, where they both earned medical degrees and master’s degrees in public health before coming to the United States in 1989 and 1990 for Ph.D. training at Johns Hopkins University and Columbia University in New York, respectively.

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