Health: Risk factors
Isolated in rural China, the ethnic Yi don't suffer from
cardiovascular diseases. But when they move to the city, leaving
their traditional life styles and diets at home in exchange for
life in the faster lane where higher fat diets and less physical
activity are the rule, they often develop higher blood pressure
and hypertension and may become overweight.
According to School of Public Health researcher Jiang He, these conclusions from a two-year study of Yi farmers and migrants have implications for making life-style dietary changes to lowering cardiovascular disease risks.
The study was jointly conducted by researchers from the Welch Center for Prevention, Epidemiology and Clinical Research at the School of Public Health and researchers in the People's Republic of China.
The study, which will appear in the Nov. 1 issue of the American Journal of Epidemiology, suggests that diets higher in fat that increase serum lipid levels--high cholesterol--when coupled with less physical activity, are leading the urban Yi not only down the path toward greater sophistication, but to cardiovascular diseases as well.
"In the 1950s, Yi farmers, who live on potatoes, rice, corn, oats and buckwheat, began to migrate to Xichang City," Jiang He said. "At home, the Yi only eat meat for celebrations, for weddings and funerals. Animal and vegetable fat are not used for cooking."
With an early interest in the health and diet of remote peoples, Jiang He began his research on the Yi when studying at Peking Union Medical College with Guan-Qing He, a co-researcher in this study and a 1940s alumnus of the School of Public Health. After coming to the school, Jiang He went back to the isolated Yi villages, 3,000 meters above sea level, to gather more data before making the connection to urban, migrant Yi.
Backpacking into the mountainous villages, Jiang He took blood pressures and drew blood to measure serum total and high density lipoprotein cholesterol and serum triglyceride levels. After testing more than 500 Yi farmers with the help of local physicians, similar tests were conducted with 300 migrants in their new urban setting. The data on the urban Yi, of Mongolian descent, were then compared with ethnic Han peoples, non-Mongolians who are the most prominent ethnic group in China and live in the same city. Information on age, cigarette smoking, alcohol consumption, nutrition and physical activity was obtained by questionnaire. Across the board, Yi migrants had higher blood pressure, higher cholesterol and engaged in less physical activity than their stay-at-home relatives. As a result, their cholesterol and other health profiles were much more like those of their new urban neighbors, the Han. According to Jiang He, the data tend to dispel the notion of a strong genetic link to higher cholesterol in favor of an environmental, life-style correlation.
"This study gave us an unusual opportunity to compare the effects of environment and ethnic heritage on serum lipid levels," said Jiang He. "Most people talk about high cholesterol as a genetic problem, running in families. This study confirmed that dietary fat and cholesterol intake--life-style eating patterns--are important in high cholesterol. The diets of the migrants were higher in fats and lower in fiber. Their cigarette smoking, alcohol consumption and lack of physical activity suggests that their new life-styles can lead to hyperlipidemia and cardiovascular diseases."
Looking at the data on cardiovascular risk and serum cholesterol levels, the cholesterol-related life-style changes put the Yi migrants at a 76 percent greater chance of developing cardiovascular illness than their relatives at home, according to Michael J. Klag, also of The Welsh Center and co-author of the study. In earlier studies, Jiang He and Klag looked at the oat and buckwheat diet of the rural Yi and found that their diet correlated with their low prevalence of cardiovascular diseases.
"Because oats and buckwheat are associated with low serum cholesterol, these foods may be useful in life-style modifications to reduce or prevent cardiovascular diseases," said Jiang He. "The lives of the rural Yi are changing because they are more in touch with the urban areas. I would like to go back to see how changes are affecting their diet and health," Jiang He added.
Go back to Previous Page