Research Report: Physical Activity Attenuates Insulin Resistance, by Late Adolescence Effect is Lost
Monday, September 28, 2015
Authors: Brad Metcalf, Joanne Hosking, William Henley, Alison Jeffery, Mohammod Mostazir, Linda Voss and Terence Wilkin, University of Exeter and Plymouth University.
Published by: Diabetologia, August 2015
Childhood obesity levels in the industrialised world are rising, with one in six children in the UK currently classed as obese. This is a concern, as obesity appears to be a factor in the development of type 2 diabetes as well as cardiovascular disease and other conditions.
Most interventions that aim to tackle obesity in children incorporate physical activity, but past research has shown activity-based interventions in children lead to only small reductions in body mass and body fat.
Nevertheless, the research team wanted to study whether activity-based interventions might have an effect on insulin resistance. Insulin resistance is a condition that leads to high blood sugar and is a precursor to type 2 diabetes.
They set out to determine to what extent physical activity in children at different ages has an impact on insulin resistance and other markers of adolescent health in this paper - Physical Activity Attenuates the Mid-adolescent Peak in Insulin Resistance But by Late Adolescence the Effect is Lost: A Longitudinal Study With Annual Measures From 9-16 Years. As part of a 12-year study into diabetes called EarlyBird, they measured insulin resistance in the same 300 children - 151 boys and 149 girls - from the age of nine to 16. The children, all from Plymouth, were fitted with accelerometers - electronic motion sensors - which they wore around their waist. The devices were set to run continuously for seven days at each of the eight annual check times. The children were asked to wear the accelerometer every day from the time they got out of bed in the morning to the time they went to bed at night, removing it only for any water-based activity. Blood samples were taken to measure serum insulin.
The young people were judged "more active" if they spent more than the median amount of time doing moderate and vigorous physical activity, which was 50 minutes a day for boys or 35 minutes a day for girls. The results showed insulin resistance was 17 per cent lower in the more active adolescents at age 12 to 13, no matter what their level of body fat. The researchers also compared young people who engaged in more activity of all kinds - not just moderate to vigorous - with their less active peers, and found these young people's insulin resistance was 14.9 per cent lower at age 12 to 13. However, over the next three years, the difference between insulin resistance in the more active young people and their less active peers diminished progressively and had disappeared completely by age 16, when insulin resistance levels were much lower in all young people. At 14, insulin resistance was 13.6 per cent lower in the more active young people than in their less active peers, at 15 it was 7.6 per cent lower and at 16 it was 1.4 per cent higher.
Implications for practice
The findings have implications for future schemes designed to reduce the insulin resistance of children and thus lower the risk of type 2 diabetes. Insulin resistance rises dramatically from age nine to 13 years, then falls steeply until age 16. The study shows physical activity reduces this early-teenage peak in insulin resistance, but has no impact at age 16. The authors suggest interventions that may seem to have failed when targeted at 16-year-olds could be successful when targeted at 12- to 13-year-olds. However, they point out this does not mean 16-year-olds do not need to be physically active.
Effect of School-based Physical Activity Interventions on Body Mass Index in Children: A Meta-analysis, Kevin Harris, Lisa Kuramoto, Michael Schulzer, Jennifer Retallack, Canadian Medical Association Journal, March 2009. An analysis of 18 studies into the effect of school-based activity programmes that found school-based physical activity interventions do not improve BMI, although they have other beneficial health effects.
Exercise and Insulin Resistance in Youth: A Meta-analysis, Michael Fedewa, Nicholas Gist, Ellen Evans, Rod Dishman, University of Georgia, Pediatrics, December 2013. An analysis of studies estimating the effectiveness of exercise on insulin resistance in children and adolescents