Fig. 2. Type 1 diabetes incidence rates per 100,000/yr in the US Virgin Islands.
clearly demonstrate that the incidence of type 1 diabetes is rising, bringing with it a large public health problem. Moreover, these findings indicate that something in our environment is changing to trigger a disease response.
Perhaps an even more interesting pattern is the epidemic nature of type 1 diabetes. Epidemics, which are rarely observed for chronic diseases, have been reported for type 1 diabetes. The first epidemic that appeared was in midwest Poland in 1984 (12). Then, the epidemic moved east. During 1985-1986, similar trends were observed in Latvia, Lithuania, and Estonia (13). If one examined the descriptive epidemiology of type 1 diabetes without knowing that it was a chronic disease, it would appear to be an infectious disorder.
In the 1980s, we reviewed all of the available temporal trend data for type 1 diabetes (14). The results were striking. More than 30% of the population-based registries worldwide exhibited epidemic trends. Most remarkable was a global pandemic of childhood diabetes that occurred between 1983 and 1984 in geographically distant populations, including Hokkaido, Japan, Auckland, New Zealand, and Poznan, Poland. Thus, epidemics of type 1 diabetes were not only focal, but they also were global.
Figure 2 presents a classic epidemic pattern from the US Virgin Islands, where the incidence of type 1 diabetes rose almost fourfold during a 1-yr period of time (15). Before the epidemic, the incidence of type 1 diabetes among these African-American children was similar to the rates observed in low-incidence populations. Then suddenly, the incidence rose to that of one of the highest rates in the world, for reasons which are not known. The following year, the incidence returned to the baseline rate. Epidemics have received little attention because they appear in retrospect. However, the locations of epidemics are likely the best places to evaluate the environmental etiology of type 1 diabetes.
Migrant studies are one of the purest designs for examining the contribution of the environment to chronic diseases. Migrant studies are based on groups of individuals that move from a source population to a host population. The magnitude and speed at
Fig. 3. Type 1 diabetes incidence rates per 100,000/yr among Chinese migrants.
which the disease incidence patterns among migrants become similar to those observed for the host population provide insight regarding potential environmental risk factors for the disease. Migrant studies have been very beneficial for studying the etiology of chronic disorders, such as cardiovascular disease and breast cancer.
The most dramatic effect of migration on type 1 diabetes incidence rates has been observed among the Chinese. There is an approximate fourfold difference in the incidence of type 1 diabetes among Chinese children living in the People's Republic of China, Taiwan, Singapore, and Hong Kong (see Fig. 3) (6). This variation may even be greater if data for Chinese migrants to the United States, the United Kingdom, or Australia were available. Similar, but less dramatic, patterns were reported for Jewish and French children living in Israel and France, respectively, compared to those who migrated to Canada (16). Interestingly, Japanese children do not appear to have been affected by migration; rates in host and source populations are similar. Thus, barring this example, temporal trend and migration data suggest that, at a minimum, 75% of all newly diagnosed type 1 diabetes cases might be prevented by modifying the environmental risk factors for the disease. If the factors contributing to the migratory effects for type 1 diabetes could be identified, the development of disease prevention strategies would be greatly facilitated.
There is now a critical need to integrate the findings of basic research into epidemio-logic research. A primary reason for this is that the missions of both basic science and epidemiology are the prevention of disease. Prevention is defined by Last as "a reduction in the incidence of a disease" (1). We also need to have epidemiologists develop systems for monitoring disorders such as type 1 diabetes. Without these approaches, we will never know whether any attempts at prevention are successful. What is even more important is that we will never know whether purported prevention strategies are doing harm.
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Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...