The science of large numbers pg. 5
The Shanghai Women’s Study has already begun to shed light on a number of areas.
Among the findings: “Women who are non-smokers but who are exposed to the cigarette smoking of their husbands have an increased risk of dying of stroke,” Zheng says. “We also learned that soy food intake reduces the risk of fractures, hypertension, coronary heart disease and diabetes.”
Simply adopting Asian eating habits may not yield the same benefits in the United States, Shu cautions.
“Even though lots of people in the South eat rice and greens, as do people in Shanghai, the specific type of vegetables and the way the food is prepared is very different,” she says.
In addition, “the ways soy foods are consumed in the U.S. are quite different from how they are consumed in China,” Shu adds. “For example, many soy products in the U.S. contain a large amount of sugar, while most soy products are consumed in China without the addition of any sugar.”
As for the Shanghai Men’s Study, which recently completed recruitment, Shu notes that the smoking rate in this cohort is high—67 percent.
“We found that smokers have a lower body-mass index than their non-smoking counterparts,” she says, “but more centralized obesity or beer belly, meaning they gain more weight around their torso. This can more be harmful to health than less centralized obesity and may increase the risk of cardiovascular disease and cancer.”
Cohort studies can yield conflicting results. For example, a 2003 study of California residents that found no relationship between environmental tobacco smoke and tobacco-related deaths contrasts sharply with a more recent finding from the Shanghai Women’s Health Study, which linked second-hand smoke to an increased incidence of cardiovascular disease, stroke and lung cancer.
While conflicting results can sometimes delay effective prevention and treatment strategies, they can also lead to new insights, says Walter Willett, M.D., MPH, Dr.P.H., professor of Epidemiology and Nutrition at the Harvard School of Public Health who launched the second Nurses’ Health Study in 1989.
“Efforts to understand the differences (between studies) can result in new knowledge,” Willett explains. “Sometimes the questions being asked are really different questions.”
Margaret Hargreaves, Ph.D., co-principal investigator of the Southern Community Cohort Study and professor of Internal Medicine at Meharry, is all too familiar with conflicting study results.
“One reason you may see conflicting findings from studies is that people may not have large enough samples when they do their research,” she notes. “That’s why we’re going for large numbers of enrollees.”
Hargreaves recalls that for a long time researchers thought obesity was closely associated with breast cancer. “Then somebody came out and said no it wasn’t, based on their findings. Now, there’s another wave of studies saying that maybe it is,” she says.
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