Purpose: The main aim of the present study (FITFATTWIN) was to investigate how physical activity level is associated with body composition, glucose homeostasis, and brain morphology in young adult male monozygotic twin pairs discordant for physical activity.
Methods: From a population-based twin cohort, we systematically selected 10 young adult male monozygotic twin pairs (age range, 32–36 yr) discordant for leisure time physical activity during the past 3 yr. On the basis of interviews, we calculated a mean sum index for leisure time and commuting activity during the past 3 yr (3-yr LTMET index expressed as MET-hours per day). We conducted extensive measurements on body composition (including fat percentage measured by dual-energy x-ray absorptiometry), glucose homeostasis including homeostatic model assessment index and insulin sensitivity index (Matsuda index, calculated from glucose and insulin values from an oral glucose tolerance test), and whole brain magnetic resonance imaging for regional volumetric analyses.
Results: According to pairwise analysis, the active twins had lower body fat percentage (P = 0.029) and homeostatic model assessment index (P = 0.031) and higher Matsuda index (P = 0.021) compared with their inactive co-twins. Striatal and prefrontal cortex (subgyral and inferior frontal gyrus) brain gray matter volumes were larger in the nondominant hemisphere in active twins compared with those in inactive co-twins, with a statistical threshold of P < 0.001.
Conclusions: Among healthy adult male twins in their mid-30s, a greater level of physical activity is associated with improved glucose homeostasis and modulation of striatum and prefrontal cortex gray matter volume, independent of genetic background. The findings may contribute to later reduced risk of type 2 diabetes and mobility limitations.
1Department of Health Sciences, University of Jyväskylä, Jyväskylä, FINLAND; 2Department of Applied Physics, University of Eastern Finland, Kuopio, FINLAND; 3Department of Psychology, University of Jyväskylä, Jyväskylä, FINLAND; 4Department of Public Health, Hjelt Institute, University of Helsinki, Helsinki, FINLAND; 5Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä, FINLAND; 6Department of Mental Health and Substance Abuse Services, National Institute for Health and Welfare, Helsinki, FINLAND; and 7Institute for Molecular Medicine, University of Helsinki, Helsinki, FINLAND
Address for correspondence: Urho M. Kujala, M.D., Ph.D., Department of Health Sciences, Sports and Health Laboratory, Rautpohjankatu 8, University of Jyväskylä, PO Box 35 (LL), FI-40014 Jyväskylä, Finland; E-mail: firstname.lastname@example.org.
Submitted for publication February 2014.
Accepted for publication June 2014.
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