Study author James P. Smith found that in 1999-2002 about 20 percent of American men who had diabetes did not know they had the disease, in contrast to 25 years ago when about half of the men with diabetes were undiagnosed.
Ethnic disparities among those with undiagnosed diabetes essentially disappeared during the same period, a sign that diabetes programs targeting minority groups have encouraged more people to get tested, according to the study appearing in the August edition of the Proceedings of the National Academy of Sciences.
"While undiagnosed diabetes remains a significant problem, we've done an excellent job of eliminating the disproportionate amount of undiagnosed disease among African-Americans and Hispanics," said James P. Smith, the study's sole author and corporate chair of labor market and demographic studies at RAND, a nonprofit research organization.
On a less positive note, Smith found that while disparities in undiagnosed diabetes disappeared over the past 25 years, new disparities have developed based upon education levels. Less educated American males are now less likely to have their diabetes diagnosed than those men with more schooling.
"If we only target disparities by race and ethnicity, we run the risk of missing other equally important health disparities that affect those least able to deal with them," Smith said.
The study also found the rate of growth of diabetes prevalence is not as high or as dramatic as often projected. Smith found that during the period studied, the proportion of men diagnosed with diabetes jumped from about 3 percent to 7 percent -- a more than doubling of the prevalence rate. However, when undiagnosed cases were considered as well, diabetes prevalence rose overall from 6 percent to 9 percent -- an increase of only 50 percent.
"Diabetes is one of the major health challenges faced across the United States, but these findings suggest that the prevalence of the disease is not growing as rapidly as often claimed," Smith said.
The study examined reasons for the rising rate of diabetes over time. The three most important reasons by far were increases in excessive weight, the transmission of diabetes from parents to children as the disease spreads, and the decline in undiagnosed diabetes. In contrast, rising levels of education actually served to reduce the prevalence of the disease.
Smith examined information from several waves of the federal National Health and Nutrition Examination Surveys conducted periodically from 1976 to 2002. The survey collects information from a nationally representative sample of adults through personal interviews, physical exams and laboratory tests. Blood tests conducted as a part of the survey allow researchers to measure undiagnosed diabetes.
Among the men studied from 1999 to 2002, Smith found that 6 percent of those with a high school diploma or more education were diagnosed with diabetes, while nearly 10 percent of those who did not obtain a high school diploma were diagnosed with the disease.
Smith found that those in the lowest education group were more likely to be Latino or African-American, less likely to engage in vigorous physical exercise and more likely to be overweight or smoke cigarettes.
Even after diagnosis, people with less education had more difficulty successfully managing the complex regimes of medicines and making the lifestyle changes needed to reduce the consequences of the illness, according to the study.
Smith said one troubling finding from the study was that people who were obese were more likely to have undiagnosed diabetes, despite the fact that obesity is the second largest risk factor for the disease following family history.
It may be that since the link between obesity and diabetes has received wide attention only in recent years, it may take more time for physicians to routinely test the obese for the disease, Smith said.
Diabetes is a serious illness that occurs when the body cannot properly produce or regulate insulin, which controls the level of glucose in the blood. The disease can cause many severe problems, including heart and kidney disease, circulatory ailments and vision problems. The illness was the sixth leading cause of death in the United States in 2002.