Because of its acute onset and obvious symptoms, type I diabetes is readily identified and, therefore, permits a more accurate picture of worldwide prevalence. Type II DM is a chronic disease with generalized symptoms; therefore, many cases are not diagnosed. However, rates of type II do appear to be increasing in developing nations. Generally, investigators have been cautious in interpreting an actual increase in the incidence of insulin-dependent DM. Prevalence rates continue to rise because of increased longevity of individuals with type I diabetes. Incidence rates for type II diabetes vary extensively by age and sex for different populations. In general, the incidence increases with age for both males and females until the sixth or seventh decade of life.
Diabetes is among the top 10 causes of death in developed countries. In Western countries, DM ranks seventh as a cause of death. Data since the early twentieth century document a decrease in early diabetes mortality because of increasing sophistication in therapeutic approaches, particularly the wide-scale use of insulin.
Migrant populations have been prone to high rates of diabetes. For example, Jews have shown increased susceptibility to diabetes in European enclaves as well as in migrant groups. Jews in New York City had rates 10 times higher than other U.S. ethnic groups. Studies from the early 1900s show high rates of diabetes among Jews in Budapest, Bengal, Boston, and Cairo. Others have shown that Sephardic Jews in Zimbabwe and Turkey have high rates of diabetes.
Early reports for Chinese populations indicate a very low prevalence of diabetes, and one researcher in 1908 observed that none of his colleagues had ever seen a case of diabetes in a Chinese patient. In modern China, rates remain very low. Most authors conclude that the Chinese have a reduced susceptibility to diabetes, although rates are somewhat higher in immigrant Chinese populations outside China. The Japanese also show a very low prevalence of diabetes in their native country, but their rates of DM increase with migration.
Amerindians, in particular, have very high rates of diabetes. The highest rates occur among the southwestern Indian groups. Yet high rates among Amerindians appear to be recent. Early reports indicated very low prevalence of diabetes among North American Indian groups at the turn of this century. Moreover, rates among South American Indian groups still tend to be low.
Other aboriginal groups also seem to be particularly prone to diabetes, among them Polynesians and Micronesians. Rates are somewhat lower among Melanesians. Hawaiians have a diabetes rate seven times higher than Caucasians in Hawaii. Among New World black populations in the West Indies and in the United States, there is a high prevalence of type II diabetes, particularly among women. Studies have also found high rates of diabetes among Mexican Americans.
One explanation of the high frequency of type II DM among these populations is that they developed a highly efficient carbohydrate metabolism under traditional lifestyles of a feast and famine cycle. The thrifty mechanisms of carbohydrate metabolism, however, became detrimental with rapidly changing lifestyles associated with a decrease in physical activity, an increase in energy in the diet, a reduction of dietary fiber, an increase of refined carbohydrates, and an increase in psychosocial stress.
Among Asian Indians, diabetes rates are low. Diabetes is more prevalent among urban populations, the rich, and the professional classes. In Indian men there also is a north-to-south gradient of diabetes prevalence, with thrice the prevalence in the south. Yet like other migrants, Asian Indians migrating to other countries show high prevalence rates compared to indigenous populations. Indians in South Africa, in particular, were brought over as indentured servants and had a lifestyle not dissimilar to that of New World black populations. A diabetes-thrifty genotype may have developed in these populations as well.
Among black Africans, DM is still comparatively rare. Nevertheless, increased prevalence has been noted for urban Africans. Apparently, for susceptible genotypes, the lifestyle changes associated with rural-to-urban migration result in higher relative risks for type II diabetes.
The foregoing data indicate that we may anticipate an increase in the worldwide prevalence of DM. The focus has been and remains on treatment of hyperglycemia and the vascular complications of long-term diabetes. Using epidemiological data and historical perspectives, we are beginning to develop better programs aimed at early intervention and prevention.
Leslie Sue Lieberman
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