To review systematically all publications of the effects of exercise on endogenous insulin-like growth factor (IGF) to clarify the nature of this association.
We reviewed 115 research studies in humans by subgroup of population (age; sex; athletic training status), physical activity exposure (resistance vs. aerobic activity; duration of activity) and study design.
Fifty percent of studies reviewed found no difference in total circulating IGF-1 as a result of exercise; 37% showed an increase, and 13% observed decreases in IGF-1 levels with exercise. Age influenced the effects of exercise on IGF levels. Exercise appeared to decrease IGF-1 levels in children, but to increase levels in young adults. Similar results were found for IGFBP-3.
It is not yet possible to determine if exercise affects IGF levels. Important methodologic differences among studies, as well as concerns about study quality, limit the ability to draw firm conclusions.
The authors are with the Division of Population Health & Information, Alberta Cancer Board, Calgary, AB T2N 4N2.