Romy Slebe1,2, Samantha B.J. Schipper1, Linda J. Schoonmade3, Denis P. Blondin4,5, David J.T. Campbell6, André C. Carpentier4,5, Jean-Pierre Després7, Joris Hoeks8, Andries Kalsbeek1,9,10, Parminder Raina11, Patrick Schrauwen12,13, Mireille J. Serlie1,9,14, Dirk Jan Stenvers1,9, Chun-Xia Yi1,9, Renée de Mutsert12, Joline W.J. Beulens1,2,15, Femke Rutters1,2, on behalf of the TIMED-consortium
1Amsterdam UMC, Amsterdam, The Netherlands; 2Amsterdam Public Health, Amsterdam, The Netherlands; 3University Library, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands; 4Centre de recherche du Centre hospitalier universitaire de Sherbrooke, Sherbrooke, Canada; 5Université de Sherbrooke, Sherbrooke, Canada; 6University of Calgary Cumming School of Medicine, Calgary, Canada; 7Université Laval, Quebec, Canada; 8Maastricht University, Maastricht, The Netherlands; 9Amsterdam Gastroenterology Endocrinology Metabolism, Amsterdam, The Netherlands; 10Netherlands Institute for Neuroscience, Amsterdam, The Netherlands; 11McMaster University, Hamilton, Ontario, Canada; 12Leiden University Medical Center, Leiden, The Netherlands; 13Heinrick Heine University Düsseldorf, Düsseldorf, Germany; 14Yale School of Medicine, New Haven, USA; 15University Medical Centre Utrecht, Utrecht, The Netherlands.
Background: Timing of physical exercise (PE) may be important for glucose metabolism, but no systematic review has combined the effects on various glycemic parameters. Therefore, we synthesize evidence on the effect of PE performed in the morning compared to the afternoon or evening on glycemic parameters in human intervention studies.
Methods: MEDLINE and Embase.com were searched for intervention studies in adults, altering the timing of one or multiple bouts of PE and examining glycemic parameters. Results were meta-analyzed in random-effects models or qualitatively described.
Results: 55,569 publications were screened using ASReview for multiple reviews on the timing of different lifestyle behaviors. 20 studies were included in this review. In acute studies (n=12), including one bout of PE, glucose levels directly after PE were 0.26mmol/L (-0.18;0.70,I2=81%) higher after morning PE, compared to afternoon PE. In studies of 1-12 weeks with repeated PE (n=8), fasting glucose was 0.25mmol/L (0.02;0.47,I2=32%) higher in morning PE, compared to afternoon or evening PE. Other outcomes (e.g. 24h mean glucose, HOMA-IR) could not be meta-analyzed, but narrative synthesis in acute and repeated PE studies showed predominately no associations or results in the same direction as described above.
Conclusions: Glucose directly after PE in acute studies and fasting glucose after repeated PE were higher after morning PE, compared to afternoon or evening PE. Results on other glycemic parameters remained inconclusive. However, our results are based on small, heterogeneous studies with differences in interventions often not taking nutritional status into account. Therefore, larger RCTs, correcting for other lifestyle behaviors, with longer follow-up periods (≥ 24 weeks) and more robust clinically relevant outcomes, such as HbA1c and lipid metabolism are needed.