Previous large-scale surveys reported that magnitudes of increase in type 2 diabetes and obesity are more remarkable among young adults than older ones, whereas prevalences of these are lower in young adults (1,2). These epidemiological findings have very important implications in clinical practice and public health policies. Despite its significance, however, there are few reports on the effects of obesity on the risk of disease in younger generations compared with older people.

We investigated the effects of BMI on the development of type 2 diabetes according to age-group in a large-scale, 10-year follow-up cohort, the Korea National Health Insurance Corporation (KNHIC) study. The KNHIC provides medical insurance to public servants, teachers, and their dependents. Of KNHIC members, 883,697 men and women aged 25–64 years in 1992 were selected as study subjects. All of the subjects were required to complete a medical questionnaire and have their general health status assessed every 2 years by the KNHIC. A more detailed description of the subjects has been published (3).

Type 2 diabetes was diagnosed when the fasting plasma glucose level is ≥126 mg/dl or subjects were treated for type 2 diabetes. BMI was categorized by 1-unit increments to examine the overall disease risks in detail with regard to the degree of obesity. In the analyses, the reference point was set as a BMI of 21 kg/m2.

We found a significant linear dose-dependent relationship between BMI and type 2 diabetes in all age-groups (all P < 0.05 for the linear trend), and these trends were more pronounced in the younger groups. The interaction between BMI and age-group was statistically significant (P = 0.003). With the reference BMI level of 21 kg/m2, subjects with a BMI of 25 kg/m2 who were between 20 and 29 years old had a relative risk of 2.24 (95% CI 1.95–2.49), while subjects aged 30–39, 40–49, and ≥50 years with this BMI had relative risks of 2.28 (2.13–2.43), 1.90 (1.78–2.02), and 1.80 (1.65–1.95), respectively. Subjects with a BMI of 30 kg/m2 who were between 20 and 29 years old had a relative risk of 6.69 (4.52–8.33), while subjects aged 30–39, 40–49, and ≥50 years with this BMI had relative risks of 4.90 (4.11–5.58), 4.09 (3.47–4.62), and 2.67 (2.05–3.17), respectively. The discrepancy between these risks increased with BMI. We found steeper dose-dependent relationships between BMI and type 2 diabetes in the younger age-groups than in the older groups.

Because type 2 diabetes leads to long-term morbidity, the prevention of obesity in younger generations and the early identification of overt disease need to be considered as critical public health issues. Therefore, public effort is needed to control weight problems and obesity in young people to prevent future health problems before it is too late.

1
Mokdad AH, Ford ES, Bowman BA, Nelson DE, Engelgau MM, Vinicor F, Marks JS: Diabetes trends in the U.S.: 1990–1998.
Diabetes Care
23
:
1278
–1283,
2000
2
Mokdad AH, Serdula MK, Dietz WH, Bowman BA, Marks JS, Koplan JP: The spread of the obesity epidemic in the United States 1991–1998.
JAMA
282
:
1519
–1522,
1999
3
Oh SW, Shin SA, Yun YH, Yoo T, Huh BY: Cut-off point of BMI and obesity-related comorbidities and mortality in middle-aged Koreans.
Obes Res
12
:
2031
–2040,
2004