Studies have confirmed the link between obesity and type 2 diabetes, but less is known about how the duration of obesity influences the development of diabetes. The longer one has an excessive body mass index, the greater the risk of developing type 2 diabetes, but race and young age also are risk factors says a study published in the January 2012 Archives of Pediatrics & Adolescent Medicine.

For this study, researchers used the National Longitudinal Survey of Youth 1979, which comprised participants between 14 and 21 years at the start. Individuals provided self-reported data on height, weight, and onset of diabetes. The retention rate as of 2006 was 81%.Of the 8,446 participants examined, 55% were white, 14% black, and 6% Hispanic. There were equal numbers of men and women. At baseline, 80% had normal weight, 15.8% were overweight, and 4.2% were obese. More blacks and Hispanics than whites were overweight and obese (16.4% versus 19.9% versus 14.9% for overweight, and 5.4% versus 5.7% versus 3.7% for obese).Also, more men than women were overweight and obese.

White men age 40 with 200 cumulative excess BMI-years had an almost threefold higher odds (OR 2.94) of developing diabetes than men of the same age and race with 100 excess BMI-years, reported Joyce M. Lee, MD, MPH, from the University of Michigan in Ann Arbor, and colleagues. However, for those with 200 excess BMI-years, researchers found a higher risk of developing diabetes among 30-year-olds compared with those at 35 and 40 years.

The increased risk among younger individuals and the increasing incidence of obesity among children, adolescents, and young adults in the U.S. mandates that "public health interventions should target younger adults," Lee and colleagues concluded. The investigators also noted that the influence of insulin resistance and beta-cell failure, both required for developing diabetes, may differ by age. Beta-cell failure has been associated with diabetes diagnosed at older ages, whereas insulin resistance is largely associated with obesity and may represent a "more important determinant for individuals diagnosed with diabetes at younger ages".