title: Independent and combined effects of physical activity and body mass index on the development of Type 2 Diabetes - a meta-analysis of 9 prospective cohort studies.
abstract: BACKGROUND
  The aim of this harmonized meta-analysis was to examine the independent and combined effects of physical activity and BMI on the incidence of type 2 diabetes.
  
  
  METHODS
  Our systematic literature review in 2011 identified 127 potentially relevant prospective studies of which 9 fulfilled the inclusion criteria (total N = 117,878, 56.2 % female, mean age = 50.0 years, range = 25-65 years). Measures of baseline physical activity (low, intermediate, high), BMI-category [BMI < 18.4 (underweight), 18.5-24.9 (normal weight), 25.0-29.9 (overweight), 30+ (obese)] and incident type 2 diabetes were harmonized across studies. The associations between physical activity, BMI and incident type 2 diabetes were analyzed using Cox regression with a standardized analysis protocol including adjustments for age, gender, educational level, and smoking. Hazard ratios from individual studies were combined in a random-effects meta-analysis.
  
  
  RESULTS
  Mean follow-up time was 9.1 years. A total of 11,237 incident type 2 diabetes cases were recorded. In mutually adjusted models, being overweight or obese (compared with normal weight) and having low physical activity (compared with high physical activity) were associated with an increased risk of incident type 2 diabetes (hazard ratios 2.33, 95 % CI 1.95-2.78; 6.10, 95 % CI: 4.63-8.04, and 1.23, 95 % CI: 1.09-1.39, respectively). Individuals who were both obese and had low physical activity had 7.4-fold (95 % CI 3.47-15.89) increased risk of type 2 diabetes compared with normal weight, high physically active participants.
  
  
  CONCLUSIONS
  This harmonized meta-analysis shows the importance of maintaining a healthy weight and being physically active in diabetes prevention.
authors.affiliation: National Institute for Public Health and the Environment, Bilthoven, The Netherlands. Laura.Cloostermans@rivm.nl.
authors.forename: Laura
authors.initials: L
authors.lastname: Cloostermans
authors.affiliation: National Institute for Public Health and the Environment, Bilthoven, The Netherlands. Wanda.Vos@rivm.nl.
authors.forename: Wanda
authors.initials: W
authors.lastname: Wendel-Vos
authors.affiliation: National Institute for Public Health and the Environment, Bilthoven, The Netherlands. Gerda.Doornbos@rivm.nl.
authors.forename: Gerda
authors.initials: G
authors.lastname: Doornbos
authors.affiliation: Baker IDI Heart and Diabetes Institute, Melbourne, VIC, Australia. Bethany.Howard@bakeridi.edu.au.
authors.forename: Bethany
authors.initials: B
authors.lastname: Howard
authors.affiliation: Canadian Fitness and Lifestyle Research Institute, Ottawa, Canada. ccraig@cflri.ca.
authors.forename: Cora Lynn
authors.initials: CL
authors.lastname: Craig
authors.affiliation: Department of Epidemiology and Public Health, University College London, London, UK. m.kivimaki@ucl.ac.uk.
authors.forename: Mika
authors.initials: M
authors.lastname: Kivimäki
authors.affiliation: Department of Epidemiology and Public Health, University College London, London, UK. a.tabak@ucl.ac.uk.
authors.forename: Adam G
authors.initials: AG
authors.lastname: Tabak
authors.affiliation: Department of Primary Care and Population Health, University College London, London, United Kingdom. b.jefferis@ucl.ac.uk.
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Jefferis
authors.affiliation: Institute of Public Health and Clinical Nutrition, University of Eastern Finland, Kuopio, Finland. kimmo.ronkainen@uef.fi.
authors.forename: Kimmo
authors.initials: K
authors.lastname: Ronkainen
authors.affiliation: School of Human Movement and Nutrition Sciences, University of Queensland, Brisbane, Australia. wbrown@hms.uq.edu.au.
authors.forename: Wendy J
authors.initials: WJ
authors.lastname: Brown
authors.affiliation: National Institute for Public Health and the Environment, Bilthoven, The Netherlands. Susan.piavet@rivm.nl.
authors.forename: Susan H S J
authors.initials: SH
authors.lastname: Picavet
authors.affiliation: Department of Clinical Epidemiology, School of Social and Community Medicine, University of Bristol, Bristol, UK. Y.Ben-Shlomo@bristol.ac.uk.
authors.forename: Yoav
authors.initials: Y
authors.lastname: Ben-Shlomo
authors.affiliation: Institute of Public Health and Clinical Nutrition, University of Eastern Finland, Kuopio, Finland. Jari.laukkanen@uef.fi.|Department of Internal Medicine, Lapland Central Hospital, Rovaniemi, Finland. Jari.laukkanen@uef.fi.
authors.forename: Jari Antero
authors.initials: JA
authors.lastname: Laukkanen
authors.affiliation: Institute of Public Health and Clinical Nutrition, University of Eastern Finland, Kuopio, Finland. Jussi.kauhanen@uef.fi.
authors.forename: Jussi
authors.initials: J
authors.lastname: Kauhanen
authors.affiliation: National Institute for Public Health and the Environment, Bilthoven, The Netherlands. Wanda.bemelmans@rivm.nl.
authors.forename: Wanda J E
authors.initials: WJ
authors.lastname: Bemelmans
mesh_terms: D000328:Adult; D000368:Aged; D015992:Body Mass Index; D001835:Body Weight; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D038622:Internationality; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology; D050177:Overweight / Q000453:epidemiology; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012306:Risk; D013851:Thinness