BANOO PARPIA: So the next question that I'd like to address is why China. What makes China so ideal for an ecologic study such as this one? And there are several features of China that lend itself very well to doing an ecologic study.
First of all, it is a very large population. As we know, China's population, in fact, at the time was 1.2 billion. It's rapidly approaching 1.5 billion. And in fact, the Chinese account for almost 1/3 of the entire world population.
The second feature of China is that there is very little physical mobility. So at the time that the study was conducted, there was a very strict residential registration system in China in place. And if we look at our survey subjects and our study population, over 90% of the survey subjects were born in the county in which they now lived.
The third feature is that there is a highly localized food production and consumption system in China. So unlike the US where there's a very large and developed infrastructure to transport food from one region of the country to another so that meals in California are virtually identical to meals in New York, this is not the case in China.
In China, there these market towns, which essentially are highly regionalized, highly specific to the specific area, and that provide service to maybe a 10 to 15 mile radius where people bicycle in or walk in to buy and sell their foods. And these foods vary enormously from one region of China or one village of China to another village. So that is in the feature that is really important.
But most importantly, we have a very wide range of disease incidence in China and a diversity of diseases across the country of China.
And these four features then allow us to view China as a very vast human laboratory in which such an ecologic study can very effectively be conducted.
Just to give an impression of how diverse and how wide this range of mortality rates is across China, let's look at how cancers range from areas that have very, very low cancer rates to those that have very high cancer rates. For example, for all cancer mortality in males, we see that it ranges from a low of 35 deaths per 100,000 to a high of about 721 deaths per 100,000. This is a 21-fold range. You look at stomach cancer mortality and you see ranges of 64 to 74. Similarly, breast cancer, there's a 20-fold range.
In this country, if we see a twofold difference, let's say, between Long Island Nassau County and Suffolk County, which have higher rates of breast cancer, a red flag goes up, and there's great concern. But in China, here, we have this range which is quite extraordinary and quite large.
An important factor about these ranges is that it increases the statistical sensitivity and allows us to really pick up relationships between nutritional factors and disease risk.
Next, to get an idea of the regionalized pattern of disease occurrence in China, I'd like to look at some maps from this atlas of cancer mortality, which gives us a very good profile of how cancer varies from cancer to cancer and from region to region in China.
But before we do this, let's review and refresh our knowledge on the geographic features of China. And that helps set the context in which we can look at some of these maps. So the topography of China is very diverse and complex. It essentially can be viewed as a series of three steppes going from north to east, starting out in Tibet.
So if we look at Tibet, this is known as the Roof of the World, as we know. And it consists of a series of high mountain ranges and some lakes and then descends down into a plateau, which has some low basins, the Turpan Basin, for example, in Xinjiang Province in Northwestern China, which is 150 meters below sea level. And then it cascades downwards towards a series of plains and finally, down to the coastal plains of rural China.
Now, most of the population in China lives in the East and along the coastal part of China and not in the southwestern, more remote part of China where they have these high mountain ranges and plateaus.
There are two main rivers also in China. One is the Yellow River in the North, and the Yangtze River, or the Long River in the South.
China also has claim to about 5,000 offshore islands, which we typically lose sight of. And those also belong to the geography of China.
The main ethnic group in China is the Han Chinese. And they constitute about 93% of the population of China. But there are also 55 different ethnic minorities in China. And each of these has different ways of eating different foods, primarily animal-based products for a lot of these minorities. And they vary quite distinctly from the majority Han Chinese.
The majority of all cancer deaths in China are from stomach, liver, and esophageal cancer.
This first slide shows that cancer is clearly a regional disease in China. We see the highest occurrence of all malignant neoplasms, which is what this map shows in males, is typically along the eastern coast of China, near Shanghai, in the big cities, Shanghai, Fujian Province, and so on.
But then we also have high rates of cancer in some of these ethnic minority populations and provinces where the ethnic minority populations dominate. And this is in Xinjiang province, in Nei Mongol or the Inner Mongolia province in China.
The next slide shows the pattern for stomach cancer in males. And here, you see a large occurrence of stomach cancer particularly in Central China and along the Eastern Seaboard. Stomach cancer is a cancer that's associated, in China, particularly with the lack of refrigeration of foods and the intake of highly salt-preserved vegetables during the winter months.
This next slide shows us the disease occurrence for colon and rectal cancer amongst males in China. And as we see, this is a completely different pattern to what we saw for stomach cancer. Colon and rectal cancer tend to occur in China along the banks of the two main rivers that I pointed out, the Yellow River and the Yangtze River. And this was a novel association that was first discovered as a result of this study. The link here is between colon cancer and a waterborne parasite known as schistosomiasis, which is thought to play a role in the predisposition towards colon cancer.
Breast cancer has a very low prevalence in China compared to the US. And as you see, it's particularly high amongst some of these ethnic minority populations, the Mongolians and the Kazakh and Uighur populations in Xinjiang Province, which typically eat a diet that is based primarily on dairy foods and animal foods. Very little fresh vegetables or fruits are eaten. No grains are eaten amongst this population. And they have extremely high rates of breast cancer.
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This study room provides a general overview and introduction to the Cornell-China-Oxford project. The project is a large and comprehensive epidemiologic study designed to explore and investigate the relationship between diet and disease.
In addition to the general descriptive findings of the study, the implications of this body of research evidence for prevention of chronic diseases such as heart disease and cancer are discussed.
This video is part 3 of 8 in the The China Project: Studying the Link Between Diet and Disease series.