Longer and sustained exposure to obesity, plus the earlier development of obesity, is linked to an increased risk of type 2 diabetes, according to US researchers.
They said that, while obesity was a well-established type 2 diabetes risk factor, little was known about the relationships between it and age of onset of obesity and cumulative exposure to obesity.
To investigate, the study authors used data from the Australian Longitudinal Study on Women’s Health (ALSWH) to identify body mass index (BMI) trends during early adult life.
They then examined the relationship between distinct BMI trajectories and the risk of diabetes and also the associations between timing of obesity onset, obese-years and diabetes.
The Australian study involved 11,192 women aged 18-23 years at the start of the research in 1996 who were followed up about every three years for up to 19 years.
A total of 162 women newly developed 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 of obesity, said the study authors from the school of public health at Indiana University.
Higher initial BMI was associated with an increased risk of diabetes. Increased age at onset of obesity was associated with a lower risk, with a 13% lower risk per one-year delay in onset.
In addition, a higher number of obese-years was associated with increased risk of developing type 2 diabetes.
The authors, led by Dr Juhua Luo, estimated that for each extra 10-obese years, the risk of diabetes increased by 25%.
The researchers also observed that women who became obese during follow-up had a three-fold increased risk of diabetes compared to women who remained not obese.
Having baseline obesity was associated with a seven-times increased risk of developing diabetes, while overweight women had a 2.3 times increased risk compared with women with normal weight.
Analysing how BMI developed through the study, those who were already obese at baseline, but who continued to put on weight rapidly on top of this had 10-times increased risk of developing diabetes, compared with normal weight women who remained stable.
Women who were overweight at baseline, and who put on weight rapidly, had a five-times increased risk of diabetes compared to the normal weight women who remained stable.
The authors said: “More than half of the women experienced a rapid BMI increase from early (18-23 years old) to middle adulthood (37-42 years old).
“Our data confirmed that BMI in young adulthood played an important role in the subsequent risk of developing type 2 diabetes during adulthood,” they said in the journal Diabetologia.
“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: “Our data also indicated that baseline BMI among young women was significantly associated with risk of developing type 2 diabetes.