A new study shows that the timing of onset of obesity is linked to the risk of type 2 diabetes. The paper, published in the journal Diabetologia, examines how the direction of BMI change, as well as the age when obesity began and the number of years a person is obese (obese-years, the product of degree and duration of obesity) over the period of early adult life are reflected in diabetes risk.
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Generally defined as a body mass index of 30 kg/m2 or more, obesity is a growing problem in the current world. Similarly, type 2 diabetes has become a hugely more common problem today than in the past decades, till there are about 500 million adults living with this condition. Obesity or overweight affects about 2.1 billion, nearly a third of the population of the world. Coming to Australian adults, about 63% have an excessive body mass index, and almost 28% are obese.
The researchers looked at over 11 000 women aged 18-23 years, who participated in the Australian Longitudinal Study on Women’s Health (ALSWH) in 1996. During the long follow-up period of up to 19 years, the women were asked to record their weights every 3 years or so. The incidence of type 2 diabetes was also calculated from self-reports.
About 162 women developed type 2 diabetes over about 16 years of follow-up, on average. The researchers also found that this group showed 6 different kinds of BMI trajectory, depending on the initial body weight and the rate of increase of BMI. On average, the BMI went up from about 22.8 to 26.9 kg/m2 at the last survey. Obesity became more prevalent, from 6.5% to 25.7% at the time of the last survey. Among the 2008 women who became obese, the mean number of obese-years was 8.4.
About 27% of women showed a stable BMI trajectory with time, while 21% showed a small increase, and over 50% had a rapid increase. Among these, those who were normal weight at the beginning but then showed rapid increase composed the largest percentage at 28%.
Those who had higher BMI at baseline were more at risk for a sedentary, high-stress, lifestyle, with more unacceptable drinking patterns, lower education and less contentment with one’s income, as well as gestational diabetes.
If a woman was normal weight at baseline, the occurrence of obesity in the follow up period tripled the risk of development of diabetes compared to those who maintained a normal weight.
The higher the BMI at baseline, the greater was the subsequent risk of diabetes. Moreover, the later the age at which the individual became obese for the first time, the lower the risk of developing diabetes was. For each one-year delay, the risk was decreased by 13%.
Lastly, the longer the duration of cumulative obesity, in terms of increased obese-years, the higher was the risk of diabetes. That is, those who became obese had a 2.18-fold increased risk of diabetes with less than 10 obese-years. With 10-29 obese-years, the risk went up by 3 times, while it increased to almost 6 times with 30 or more obese-years, compared with that of a woman who remained non-obese throughout the follow-up period.
The greatest risk of diabetes was with women who were high-BMI at baseline and showed rapid increase in weight thereafter, at 10-fold compared to 7-fold in those who were obese at baseline but did not increase rapidly. Overweight women whose weight increased rapidly had 4.75 times the risk of diabetes compared to normal weight women, compared to the 2.33 times increased risk of those who were overweight but remained at the same trajectory.
The study thus shows that the risk of type 2 diabetes varies with respect to the timing of obesity in early adult life, and the overall build-up of obesity duration during this period, in young women. This could be related to either the increased duration of obesity, or the ill-effects of obesity of early onset on insulin metabolism at an early age. If obesity persists for a long period, it causes excess fat tissue to build up. This can further alter the metabolism, leading to a pro-inflammatory state and increased insulin resistance in the peripheral tissues, predisposing to diabetes.
Simply delaying the onset of obesity and the total number of years when obesity is present could effectively reduce the risk of diabetes. Early prevention of diabetes via proper management of adolescent obesity is thus very important.
Luo, J., Hodge, A., Hendryx, M. et al. Age of obesity onset, cumulative obesity exposure over early adulthood and risk of type 2 diabetes. Diabetologia (2019) doi:10.1007/s00125-019-05058-7, https://link.springer.com/article/10.1007%2Fs00125-019-05058-7