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More Years Obese Equals More Diabetes Risk

Jan 6, 2012

A longitudinal analysis found that, the longer one has an excessive BMI, the greater the risk of developing type 2 diabetes, but race and young age also are risk factors.

Joyce M. Lee, MD, MPH, from the University of Michigan in Ann Arbor, and colleagues reported that, 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.

However, according to the published study, 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.

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. Studies examining this aspect were based on unique populations or used crude measures of duration, researchers noted, limiting their applicability to the broad U.S. population.

The researchers wrote: “Understanding the impact of both degree and duration of obesity on incident type 2 diabetes is critical, given the childhood obesity epidemic.”

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 for this study, 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.

The investigators defined excess BMI for a particular year as the participant’s actual BMI minus the reference BMI. The reference BMI was defined as BMI thresholds for overweight of 25.0 for adults and 85th percentile for adolescents.

“For example,” they explained, “23.4 corresponds to the 85th percentile for a boy aged 15 years; the degree of obesity for a BMI of 25.0 would be 25.0−23.4=1.6.” They then totaled excess BMI for all previous years to calculate excess BMI-years.

By 2006, 4.1% of the participants had developed diabetes, including considerably more Hispanics (7%) and blacks (4.8%) than whites (2.4%), and a slightly higher percentage of women (4.4%) than men (3.8%). However, the average age at onset of diabetes was similar across all categories (between 36 and 37).

Overall, a higher level of excess BMI-years was associated with a greater risk of developing diabetes. For example, white men in their 40s with 200 excess BMI-years had a greater risk of self-reported diabetes (OR 2.94, 95% CI 2.36 to 3.67) than white men in their 40s with 100 excess BMI-years.

However, Hispanics and blacks at age 30 with 200 excess BMI-years had a greater risk than whites with the same level of excess BMI-years. The trend continued for Hispanics at 35 years, but declined slightly for blacks.

Researchers were unsure why an excess of BMI was more detrimental for younger rather than older participants for the onset of diabetes. They hypothesized that “a given amount of excess BMI when carried earlier in the life course may be more diabetogenic than the same amount of weight carried later in the life course.”

In parallel with this finding is the increasing obesity among adolescents, which may result in “steeper increases in diabetes for younger compared with older adults,” they said.

If further studies confirm these findings, it may be more advantageous to aim prevention programs at younger people, Lee and colleagues wrote.

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.”

Practice Pearls:  

  • All data were self-reported, but those with a particular number of excess BMI-years by age 30 had a higher risk of diabetes than individuals who had accumulated the same number of excess BMI-years by age 40.
  • This longitudinal study found that individuals with a higher BMI for a longer period of time had a increased risk of self-reported type 2 diabetes.

Lee JM, et al “Excess body mass index–years, a measure of degree and duration of excess weight, and risk for incident diabetes” Arch Pediatr Adolesc Med 2012; 166(1): 42-48.