BMI history and risk of type 2 diabetes
Evidence from several epidemiologic studies indicates that obesity and weight gain are causally related to type 2 diabetes. Many studies have reported a higher diabetes risk in men(1-5) and women(4,6,7) with increasing BMI (kg/m2) and weight gain in adolescence(1,6). The duration of overweight seems to be another significant risk factor for diabetes independent of the current degree of obesity(8,9). Although considerable scientific work has been done on the association between overweight and diabetes, no study has explicitly quantified whether or how body weight changes during different periods in adult life are related to risk of type 2 diabetes. The topic is even more interesting since the prevalence of obesity and diabetes have increased substantially over the last decades(10) and large segments of the population are starting to gain weight early in adult life, after settling into an occupation or family life. Data from adults in westernized countries show that the largest increase in the prevalence of obesity in men and women is seen in younger life, between age 20 and 40 years(11-13).
Observations from the EPIC Study
An investigation was conducted to compare two different periods in adult life with regard to the association between weight change and risk of diabetes(14). The study population included 7,720 men and 10,371 women from the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam cohort(15), a population sample of 27,548 participants contributing to the (EPIC)-Potsdam Study, a large multicenter cohort to study the association between nutrition and chronic disease(16). The baseline examinations included anthropometric measurements and face-to-face interviews on sociodemographic characteristics. Follow-up questionnaires for information on incident diseases were collected every two to three years and self-reported diabetes cases were verified by the treating physician. The mean percentage of BMI change between ages 25 and 40 y was highest (10%) in men and women with a BMI less than 23.0kg/m2 at age 25 years. For a BMI between 23.0 and 25.0 the mean percentage change of BMI was 7%-8%, and for overweight men and women it was 5.5%. Women had higher percentages of BMI change between 40 to 55 y in all categories of BMI at age 25 y (12%-14%) whereas the percentage of BMI change for men increased slightly by 8%-10% compared with the earlier period. Using a multivariate model, the relative risk of diabetes for men and women was slightly higher for a BMI change between 25 and 40 y (about 25% higher risk for a 1-unit increase in BMI) than for a BMI change between 40 and 55y (12% higher risk). The stronger association of risk with weight gain in early adulthood than in later life might be explained by the longer duration of exposure to excessive body fat. Previous studies already identified that obesity lasting 5 y and longer is an important risk factor for type 2 diabetes(8,9).
Effect of weight history
To determine risk related to different weight change histories, the BMI changes were categorized into three groups: ”loss or stable” (loss or gain of less than 1 BMI unit over 15 y), “moderate gain” (gain of 1.0-4.0 kg/m2) and “severe gain” (gain of more than 4.0 kg/m2). Severe weight gain between age 25 and 40 y and stable weight management between 40 and 55 y was associated with a 1.5-times higher risk for diabetes in men and a 4.3-times higher risk in women compared with those of stable management in early adulthood and severe gains later in life. An explanation for the higher risks among women than men with moderate or severe BMI gain during early adulthood could be the relation between parity and obesity. The childbearing years have been identified as a critical period for substantial excess weight gain and development of obesity, which cannot be explained by behavioural changes(17). Risk was not increased for those who were overweight at age 25 y and had lost weight or maintained weight during the same periods compared with normal weight people whose weight was stable until age 55 y. However, even modest weight gain in adult life is associated with a substantial risk of developing type 2 diabetes, and moderate or severe weight gain in early life is a stronger risk factor for diabetes than is weight gain after age 40 y. This stresses the importance of maintaining a healthy body weight throughout life.
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