The China Study - T. Colin Campbell and Thomas M. Campbell

ExperimentalDesign of the China Study

SIXTY-FIVE COUNTIES in twenty-four different provinces (out of twenty- seven) were selected for the survey. They represented the full range of mortality rates for seven of the more common cancers. They also provided broad geographic coverage and were within four hours' travel time of a central laboratory. The survey counties represented:
• semitropical coastal areas of southeast China;
• frigid wintry areas in northeast China, near Siberia;
• areas near the Great Gobi desert and the northern steppes;
• and areas near or in the Himalaya Mountains ranging from the far
northwest to the far southwest part of the country.
Except for suburban areas near Shanghai, most counties were located in rural China where people lived in the same place their entire lives and consumed locally produced food. Population densities varied wide- ly, from 20,000 nomadic residents for the most remote county near the Great Gobi desert, to 1.3 million people for the county on the outskirts of Shanghai.
This survey is referred to as an ecological or correlation study design, meaning that we are comparing diet, lifestyle and disease characteristics of a number of sample populations, in this case the sixy-five counties. We determine how these characteristics, as county averages, correlate
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or associate with each other. For example, how does dietary fat relate to breast cancer rates? Or how does blood cholesterol relate to coronary heart disease? How does a certain kind of fatty acid in red blood cells relate to rice consumption? We could also compare blood testosterone levels or estrogen levels with breast cancer risk. We did thousands of different comparisons of this type.
In a study of this kind, it is important to note that only the average values for county populations are being compared. Individuals are not being compared with individuals (in reality, neither does any other epi- demiological study design). As ecological studies go, this study, with its sixy-five counties, was unusually large. Most such studies only have ten to twenty such population units, at most.
Each of the Sixty-five counties provided 100 adults for the survey. One-half were male and one-half female, all aged thirty-five to sixty- four years. The data were collected in the following manner:
• each person volunteered a blood sample and completed a diet and lifestyle questionnaire;
• one-halfofthepeopleprovidedaurinesample;
• the survey teams went to 30% of the homes to carefully measure
food consumed by the family over a three-day period;
• samples of food representing the typical diets at each survey site were collected at the local marketplace and were later analyzed for
dietary and nutritional factors.
One of the more important questions during the early planning stages was how to survey for diet and nutrition information. Estimating consumption of food and nutrients from memory is a common method, but this is very imprecise, especially when mixed dishes are consumed. Can you remember what foods you ate last week, or even yesterday? Can you remember how much? Another even more crude method of estimating food intake is to see how much of each food is sold in the marketplace. These findings can give reasonable estimates of diet trends over time for whole populations, but they do not account for food waste or measure individual amounts of consumption.
Although each of these relatively crude methods can be useful for certain purposes, they still are subject to considerable technical error and personal bias. And the bigger the technical error, the more difficult it is to detect significant cause-effect associations.
We wanted to do better than crudely measure which foods and how

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much of these foods were being consumed. Thus we decided to evaluate nutritional conditions by analyzing blood and urine samples for indica- tors (biomarkers) of multiple nutrient intakes. These analyses would be far more objective than haVing people recall what they ate.
Collecting and analyzing blood, however, was not easy to arrange, at least not in the way that we preferred. The initial problem was getting enough blood. For cultural reasons, rural Chinese were reluctant to pro- vide blood samples. A finger prick seemed to be the only possibility but this was not good enough. A regular vial of blood would give 100 times as much blood and allow for analyses of many more factors.
Dr. Junshi Chen of our team, at the Institute of Nutrition and Food Hygiene in the Ministry of Health, had the unenviable task of convinc- ing these volunteers to give a regular vial of blood. He succeeded. Sir Richard Peto at the University of Oxford of our team then made the very practical suggestion of combining the individual blood samples to make a big pool of blood for each village for each sex. This strategy gave more than 1,200-1,300 times more blood when compared with the finger prick method.
Making big pools of blood had enormous implications and made possible the China Study, as it later became known. It allowed analyses of far more indicators of diet and health. This allowed us to consider relationships in a far more comprehensive manner than would have otherwise been possible. For more detail on the theoretical and practical basis for collecting and analyzing blood in this way the reader is referred to the original monograph of the study.l
After collecting the blood, we then had to decide who would do the many analyses that were pOSSible. We wanted nothing but the best. While some analyses were conducted at our Cornell lab and at Dr. Chen's Beijing lab, the rest of the analyses, especially the more special- ized types, were done in about two dozen laboratories located in six countries and in four continents. Laboratories were selected because of their demonstrated expertise and interest. The laboratory participants
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HOW GOOD IS THIS STUDY?
Because this survey was a one-of-a-kind opportunity, we intended that it be the best of its kind ever undertaken. It was comprehensive; it was high quality; and its uniqueness allowed new opportunities to inves- tigate diet and disease that were never before possible. These features
are listed in the original monograph.