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Diabetes: Type 2

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Description

An in-depth report on the causes, diagnosis, treatment, and prevention of type 2 diabetes.

Alternative Names

Maturity Onset Diabetes; Noninsulin-dependent Diabetes Mellitus

Risk Factors

At this time, about 15.6 million Americans have diabetes; up to 95% of these cases are type 2. The prevalence of type 2 diabetes increased from 4.9% in 1990 to nearly 7% in 1999. Historically, type 2 diabetes usually developed after the age of 40, but it is now also increasing in children. Given the current epidemic of obesity, experts are now estimating that over a third of all people born in 2002 will eventually develop diabetes. Furthermore, the dramatic increase in diabetes is occurring worldwide as American lifestyles become global. Evidence strongly suggests that healthy lifestyles can prevent most cases of type 2 diabetes.

Obesity and Metabolic Syndrome

Obesity is the number one risk factor for type 2 diabetes. It is estimated that 80% to 95% of the current dramatic increases in type 2 diabetes are due to obesity. Excess body fat appears to play a strong role in insulin resistance, but the way the fat is distributed is also significant. Weight concentrated around the abdomen and in the upper part of the body (apple-shaped) is associated with insulin resistance and diabetes, heart disease, high blood pressure, stroke, and unhealthy cholesterol levels. Waist circumferences greater than 35 inches in women and 40 inches in men have been specifically associated with a greater risk for heart disease and diabetes. (People with a "pear-shape"--fat that settles around the hips and flank--appear to have a lower risk for with these conditions.) Of note: obesity does not explain all cases of type 2 diabetes. It is also common among people in countries where weights tend to be low, such as Asia or India.

Metabolic Syndrome. A set of conditions referred to as metabolic syndrome (also called syndrome X) is a pre-diabetic condition that is significantly associated with heart disease and higher mortality rates from all causes. The syndrome consists of obesity marked by abdominal fat, unhealthy cholesterol levels, high blood pressure, and insulin resistance. A 2002 study estimated that nearly a quarter of the U.S. population now has this condition. Even worse, according to a 2003 study, nearly a million American teenagers have this syndrome.

Family History

Between 25% and 33% of all type 2 patients have family members with diabetes. Having a first-degree relative with the disease poses a 40% risk of developing diabetes. One study reported that people with positive family histories have a higher risk for developing the disease at an earlier stage with more severe features. Because families share many lifestyle features (eating and exercise habits) it is difficult to determine when genetics or environment play the major role. When clusters of diabetes type 1 and 2 appear within families, genetic factors should be strongly suspected.

Ethnicity

The risk for type 2 diabetes varies among population groups. Diabetes also seems to pose higher or lower risks for specific complications among ethnic groups. Genetic, socioeconomic factors, or both seem to be involved in some ethnic differences, but in most cases the observed increase in ethnic groups in Americans is due to changes in traditional lifestyles.

African Americans. African American men have one and a half times the risk of developing type 2 diabetes and African American women have twice the risk as their Caucasian peers. African Americans with diabetes are also at higher risk for amputations than diabetic Caucasians. This is most likely due to a higher incidence of high blood pressure and smoking as well as poorer health care in African Americans. Genetic factors also play a role. For example, there is some evidence that African Americans process insulin in the liver differently from Caucasians, which may make them more susceptible to diabetes when other risk factors are present.
Native Americans. The Pima tribe in Arizona has an incidence of type 2 diabetes that is 19 times higher than that of the white population. The risk for diabetic complications among young Pima adults is also very high. Other Native American tribes in North America are also at high risk for type 2 diabetes. The association between diet and diabetes among this population remains critical, however, in assessing the reason for their higher risk. For example, in one study, Pimas who lived in Mexico exercised more and ate less fat (but consumed more calories) than Pima tribes in Arizona. Mexican Pimas have a prevalence of diabetes of only 6%, while half of their Arizona Pima neighbors had diabetes.
Hispanic Americans. The rate of type 2 diabetes is also very high among Mexican Americans, approximately double that for Caucasians. This group may also be at higher risk for heart problems than other ethnic groups with diabetes.

Low Birth Weight

Low birth weight is now a recognized risk factor for type 2 diabetes and heart disease in adulthood. The reasons are unclear, although recent studies are suggesting it may represent a genetic factor. Studies in 2002 and 2003 observed that babies of fathers with type 2 diabetes and of women who later developed type 2 diabetes tended to weigh less than babies of parents without diabetes. Such studies suggest that such parents may have some specific gene that affects insulin factors, putting both themselves and their children at risk for future diabetes. Theoretically, such a gene might also affect insulin factors in the developing fetus, causing low birth weight. (Of note, mothers of very high-weight babies are also at risk for diabetes -- although in these cases it is most often associated with gestational diabetes.)

Diabetes in Children and Adolescents

Obesity-Related Type 2 Diabetes in Children. Until recent years, diabetes in children was almost always type 1 (an autoimmune disease). Between 1982 and 1994, however, the incidence of type 2 diabetes in children multiplied by ten, until in 1996, a study reported that a third of all new diabetes cases in children were type 2. This increase parallels the rising epidemic in childhood obesity that has occurred both in the US and worldwide, notably Europe and Japan. In some areas of Japan, type 2 diabetes has now become the dominant form of diabetes in children and adolescents. Obesity in children is also related to abnormalities in cholesterol, blood pressure, and insulin levels in adults. Administering glucose tolerance tests in overweight children may be helpful in identifying those at high risk for diabetes.

Maturity-Onset Diabetes in Caucasian Youth. Maturity-onset diabetes in youth (MODY) is a rare genetic form of type 2 diabetes that develops only in Caucasian teenagers. It accounts for 2% to 5% of type 2 cases. (This form of type 2 diabetes is not associated with obesity.)

Diabetes in the Pregnant Woman (Gestational Diabetes)

An estimated 5% of pregnant women develop a form of type 2 diabetes, usually temporary, in their third trimester called gestational diabetes.

Gestational Diabetes

Gestational diabetes is a diabetic condition (nearly always temporary) that develops during the third trimester. After delivery, blood glucose levels generally return to normal, although between one-third and one-half of these women develop type 2 diabetes within 10 years.

Who Gets Gestational Diabetes?

Estimates for the prevalence of gestational diabetes are generally about 4%. Some studies, however, have suggested significantly higher rates. In one German study, 13% of pregnant women were diagnosed with this form of diabetes, including many who did not have any risk factors.

Risk factors include the following:

Weight gain (11 to 22 pounds) during early adulthood.
Family history of diabetes.
Smoking.
Belonging to African American, Hispanic, or Asian ethnic groups.
Gaining weight before getting pregnant.
Being an older mother.

It should be noted that some studies suggest that women who develop gestational diabetes during pregnancy and take progestin-only contraceptives while breast-feeding are at high risk for developing full-blown type 2 diabetes.

Who Should Be Tested for Gestational Diabetes?

A number of expert groups now recommend that nearly all pregnant women be tested for gestational diabetes between their 24th and 28th week. Pregnant women at high risk for diabetes should be tested earlier. The only women who do not need to be tested are those at very low risk. Generally they have the following characteristics:

Under 25 years old.
Normal weight.
No first-degree relatives with diabetes.
Not belonging to the following ethnic groups: Native American, Hispanic, Asian or African-American.

How Serious Is Diabetes During Pregnancy?

Effect of Diabetes on the Fetus. Because glucose crosses the placenta, a woman with diabetes can pass high levels of blood glucose to the fetus. In response, the fetus secretes high level of insulin. Studies indicate that such conditions may effect the developing fetus as soon as it is conceived, placing the unborn child at risk for the following:

Birth defects. (It should be noted that the risk is significant only in women who had diabetes before they became pregnant. A 2002 study reported no excess risk for infant malformations in women with gestational diabetes.)
Excessive growth of the fetus.
Delayed lung development.
Possibly a higher risk for future diabetes and obesity in the child.

Effect of Diabetes on the Pregnant Woman. In addition to endangering the fetus, diabetes also presents risks to the pregnant woman.

In one German study, 25% of women with gestational diabetes required a cesarean section. (The non-diabetic rate in the study was also high however, 19.6%.)

The most serious potential complications from diabetes are high blood pressure and preeclampsia, a potentially dangerous condition. In one study, blood pressure was abnormally high in 6.5% of women with gestational diabetes compared to 1.7% of pregnant women without diabetes. (Note that one study suggested mortality rates in pregnant women with gestational diabetes vary widely, and normal rates have been reported in some countries, suggesting that good prenatal care can be fully protective.)

How Is Gestational Diabetes Managed?

Some suggestions for preventing complications include the following:

In most cases, increases in glucose levels can be managed with diet and exercise. Aerobic exercise before and during pregnancy may lower glucose levels and may be protective for women at risk or who have gestational diabetes. (Any pregnant woman should check with her physician before embarking on a vigorous exercise regimen.)
If a woman with gestational diabetes cannot keep her glucose under control with lifestyle measures, then she usually is given insulin.
Oral agents commonly used for type 2 diabetes have not been routinely prescribed because of a higher risk for birth defects and severe hypoglycemia in the newborn. Studies suggest that newer agents, such as glyburide, however, may be effective and safe alternatives to insulin.

The placenta provides the fetus with oxygen and nutrients and takes away waste such as carbon dioxide via the umbilical cord.

Other Medical Conditions

Polycystic Ovary Syndrome. Polycystic ovary syndrome (PCO) is a condition that affects about 6% of women and results in the ovarian production of high amounts of androgens (male hormones), particularly testosterone. It appears to be an important cause of many menstrual disorders. Women with PCO are at higher risk for insulin resistance, and about half of PCO patients also have diabetes.

Click the icon to see an image of polycystic ovary syndrome.

Hepatitis C. Patients with hepatitis C have a higher incidence of type 2 diabetes. The reasons for this are unclear.

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