New York, Dec 23 (IANS): Researchers have found that longer and sustained exposure to obesity is linked to an increased risk of type 2 diabetes.

For the findings, published in the journal Diabetologia, the research team from Indiana University in the US, used data from the Australian Longitudinal Study on Women's Health (ALSWH) to identify body mass index (BMI) trajectories over the early adult life course.

They then examined the relationship between distinct BMI trajectories and risk of type 2 diabetes. Also investigated were the associations between timing of obesity onset, obese-years and type 2 diabetes.

"Our data also indicated that baseline BMI among young women was significantly associated with risk of developing type 2 diabetes," said the study researchers from Indiana University in the US.

"The results highlight the importance of overweight or obesity in early adulthood as risk factors for adult diabetes, indicating that weight control starting before early adulthood is critical for reducing type 2 diabetes risk in later life," they added.

Women aged 18-23 years at baseline (number of participants was 11,192) enrolled in the ALSWH in 1996 were followed up about every three years via surveys for up to 19 years. Self-reported weights were collected up to seven times.

New cases of type 2 diabetes were self-reported. A total of 162 (1.5 per cent) women newly developed type 2 diabetes over an average of 16 years of follow-up.

Six distinct BMI trajectories were identified, varying by different initial BMI and different rates of increase in obesity.

Higher initial BMI was associated with an increased risk of diabetes. Increased age at onset of obesity was associated with a lower risk of diabetes, with a 13 per cent lower risk of developing type 2 diabetes per one-year delay in onset.

A higher number of obese-years was associated with increased risk of developing type 2 diabetes.

Obese years is calculated by person's BMI minus the BMI for obesity (30), then multiplying by the number of years of exposure.

The authors estimate that for each extra 10-obese years, the risk of diabetes increased by 25 per cent.

Among 10,521 women who were not obese at baseline, the researchers observed that women who became obese during follow-up had a 3-fold increased risk of type 2 diabetes compared to women who remained not obese.

More specifically, compared with women who did not become obese during the follow-up, women who became obese and had obese-years of <10, 10 to under 30, and 30 or more had increased risks of developing type 2 diabetes of two, three and six times, respectively.

Results of analysis using only the women's initial (baseline) BMI found that having baseline obesity (a BMI of 30 or more) was associated with a 7-times increased risk of developing diabetes, while overweight women (BMI 25.0 to 29.9) had a 2.3 times increased risk compared with women with normal weight.

"Our data confirmed that BMI in young adulthood played an important role in the subsequent risk of developing type 2 diabetes during adulthood," the researchers said.

"We also observed that women who were non-obese at baseline, but became obese during follow-up had a higher risk of type 2 diabetes relative to women who stayed non-obese; the younger the age at onset of obesity or the greater the obese-years, the higher the risk of type 2 diabetes," they added.