Becoming obese earlier in life linked to increased risk of type 2 diabetes

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New research has found that the number of years an individual is obese may be linked to a higher risk of developing type 2 diabetes.

Carried out by researchers at Indiana University, USA, along with the University of Melbourne and University of Newcastle, Australia, the new study looked at 11,192 women taking part in the Australian Longitudinal Study on Women's Health (ALSWH).

The women were aged between 18 and 23 at the start of the study, and followed for a period of 19 years. During this time, the women self-reported their weight up to seven times, and self-reported any diagnosis of type 2 diabetes.

The findings, published in Diabetologia, showed that a higher body mass index (BMI) was associated with an increased risk of diabetes. More specifically, being obese at the start of the study (defined as having a BMI of 30 or more) was associated with a 7-times increased risk of developing diabetes, while overweight women (defined as having a BMI of 25.0 to 29.9) had a 2.3 times increased risk, compared with women of normal weight.

In addition, the women who were not obese at the start of the study but who became obese during the follow-up had a 3-fold increased risk of type 2 diabetes compared to women who did not become obese. Those who were already obese at the start and continued to put on weight rapidly had a 10-times increased risk of developing diabetes compared with normal-weight women who remained stable.

Women who had a higher number of obese-years also had an increased risk of developing type 2 diabetes. The researchers explained that the obese-years figure is calculated by taking a person's BMI, subtracting the BMI for obesity (which is 30), and multiplying that by the number of years spent being obese. The authors estimated that for every extra 10-obese years, the risk of diabetes increased by 25 percent.

Becoming obese at an older age was also associated with a lower risk of diabetes; the study found a 13 percent lower risk of developing the condition per one-year delay in onset.

The researchers noted that the findings held true even after accounting for factors such as the number of children the women had and their diet. They added that their study highlights "the importance of preventing or delaying the onset of obesity and reducing cumulative exposure to obesity to substantially lower the risk of developing diabetes. We recommend that people self-monitor weight change over time, and that health care providers look at weight change in addition to current weight as another risk factor for diabetes."