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Sunday, July 4, 2004

Diabetes explosion: What does it really mean?



By Dr. Daniel W. Nebert
Guest columnist

Scientists at the Centers for Disease Control and Prevention recently warned that one of every three U.S. children who were born in 2000 will become diabetic. Obesity and type-2 diabetes go hand-in-hand.

This country needs to become serious about eating less and exercising more; from age 3 or younger, the child of today is exposed to more television and computer games, less exercise and outdoor activities, and far more fast food. But, is there something beyond this simple solution that we are not appreciating?

Type 1 diabetes is insulin-dependent and associated with autoimmune disease (in which a person's antibodies destroy the pancreas insulin-producing beta cells) and maybe with viral infections. If you don't make insulin, your blood sugar goes sky-high. These patients are thin and prone to hyperglycemia (elevated blood sugar).

Type 2 diabetes is non-insulin-dependent (altered insulin secretion and insulin resistance). Your insulin levels can be normal, but the insulin is unable to gain access to the pathways that lower blood sugar. These patients are overweight, and the disease is brought on more quickly (at an earlier age) by obesity. But why are we now having an epidemic of type 2 diabetes in the United States?

In 1962, professor James V. Neel of the University of Michigan presented his "thrifty gene" hypothesis, which is directly relevant to this epidemic. Neel's theory suggests that advantageous mutations in genes can "evolve," over several generations, in response to selective pressures.

Having children, propagation of the species, is the most important factor for each family; adults having a reproductive disadvantage (i.e. those not responding favorably to selective pressures, such as diet) are less likely to contribute children to the next generation. For example, humans of long ago who lived as peasants in 15th-century Europe or Africa experienced conditions of predictably alternating feast-and-famine, which became the traditional lifestyle. What would happen if such people were suddenly given a modern world where food is abundant all the time and exercise is avoided?

Last year, professor Jared Diamond of the UCLA Medical Center offered a hypothesis as to why the United States is seeing this explosion in type 2 diabetes today. The lowest prevalence (practically zero) of type 2 diabetes in the world is in rural Third World areas. The highest prevalence (37 percent to 50 percent) is seen among Nauru Islanders of the tropical Pacific, Pima Indians in Arizona, and urban Wanigela people in Papua New Guinea. Each of the latter three populations has undergone a sudden change, in just one to three generations, from famine to a sedentary life with plentiful food.

In contrast, European populations have undergone a gradual change (from less eating/more exercise to more eating/less exercise), over at least 25 generations, between the 1400s and 1800s.

The U.S. population presents almost completely a melting pot of ethnic groups arriving from various other parts of the world. European Americans have emigrated from their society, which has undergone four to five centuries of gradual change from high activity to less activity. African-Americans largely came to the United States as a population that has undergone a sudden change, in just a few generations, from famine to a sedentary life with plentiful food. Hispanic-Americans are the latest ethnic group to have emigrated in large numbers to the United States from a rural Third World region to a sudden change to sedentary lifestyle.

What do these ethnic differences, among the various populations that now make up the United States, have to do with the CDC's recent prediction that one of every three U.S. children born in 2000 will become overweight and diabetic? It is likely that, of children born in 2000, 8 percent of European-Americans, more than 50 percent of African-Americans, and more than 60 percent of Hispanic-Americans will develop obesity and type 2 diabetes. Combined, the total will be one of every three children born in 2000.

Each of us in the community - parents, teachers, school administrators, athletic coaches, law-enforcement officers, practicing physicians - should be aware, and be tolerant, that some children are more prone than others to developing obesity and type 2 diabetes. The problem is sort of "in our genes" or, at least, passed down by the genes from our grandparents and great-great-great-grandparents.

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Dr. Daniel W. Nebert is a professor at the University of Cincinnati Medical Center and is board-qualified in pediatrics and human genetics. He directs a lab studying whyindividuals respond differently to the same dose of a drug, cigarette smoke or other environmental chemical.




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