title: Effect of physical activity on sex hormones in women: a systematic review and meta-analysis of randomized controlled trials.
abstract: BACKGROUND
  Exposure to high levels of endogenous estrogens is a main risk factor for breast cancer in women, and in observational studies was found to be inversely associated with physical activity. The objective of the present study is to determine the effect of physical activity interventions on sex hormone levels in healthy women.
  
  
  METHODS
  Electronic databases (MEDLINE, EMBASE, CENTRAL), from inception to December 2014, and reference lists of relevant reviews and clinical trials were searched, with no language restrictions applied. Randomized controlled trials (RCTs) were included if they compared any type of exercise intervention to no intervention or other interventions, and assessed the effects on estrogens, androgens or the sex hormone binding globulin (SHBG) in cancer-free women. Following the method described in the Cochrane Handbook for Systematic Reviews of Interventions, data on populations, interventions, and outcomes were extracted, and combined using the inverse-variance method and a random-effects model. A pre-established protocol was drawn up, in which the primary outcome was the difference in circulating estradiol concentrations between the physical activity (experimental) and the control groups after intervention. Pre-specified subgroup analyses and sensitivity analysis according to the risk of bias were conducted.
  
  
  RESULTS
  Data suitable for quantitative synthesis were available from 18 RCTs (1994 participants) for total estradiol and from 5 RCTs (1245 participants) for free estradiol. The overall effect of physical activity was a statistically significant decrease of both total estradiol (standardized mean difference [SMD] -0.12; 95 % confidence interval [CI] -0.20 to -0.03; P = 0.01; I (2) = 0 %) and free estradiol (SMD -0.20; 95 % CI -0.31 to -0.09; P = 0.0005; I (2) = 0 %). Subgroup analyses suggest that this effect is independent of menopausal status and is more noticeable for non-obese women and for high intensity exercise. Meta-analysis for secondary outcomes found that physical activity induces a statistically significant decline of free testosterone, androstenedione, dehydroepiandrosterone-sulfate and adiposity markers, while a significant increase of SHBG was observed.
  
  
  CONCLUSIONS
  Although the effect is relatively modest, physical activity induces a decrease in circulating sex hormones and this effect is not entirely explained by weight loss. The findings emphasize the benefits of physical activity for women.
authors.affiliation: Axe Oncologie, Centre de recherche du CHU de Québec-Université Laval, St-Sacrement Hospital, 1050 chemin Sainte-Foy, Quebec City, QC, Canada, G1S 4L8. kaoutar.ennour-idrissi.1@ulaval.ca.|Centre de recherche sur le cancer, Université Laval, St-Sacrement Hospital, 1050 chemin Sainte-Foy, Quebec City, QC, Canada, G1S 4L8. kaoutar.ennour-idrissi.1@ulaval.ca.|Département de médecine sociale et préventive, Faculté de médecine, Pavillon Ferdinand-Vandry, Loc 2428, Université Laval, 1050 avenue de la Médecine, Quebec City, QC, Canada, G1V 0A6. kaoutar.ennour-idrissi.1@ulaval.ca.
authors.forename: Kaoutar
authors.initials: K
authors.lastname: Ennour-Idrissi
authors.affiliation: Axe Oncologie, Centre de recherche du CHU de Québec-Université Laval, St-Sacrement Hospital, 1050 chemin Sainte-Foy, Quebec City, QC, Canada, G1S 4L8. elizabeth.maunsell@fmed.ulaval.|Centre de recherche sur le cancer, Université Laval, St-Sacrement Hospital, 1050 chemin Sainte-Foy, Quebec City, QC, Canada, G1S 4L8. elizabeth.maunsell@fmed.ulaval.|Département de médecine sociale et préventive, Faculté de médecine, Pavillon Ferdinand-Vandry, Loc 2428, Université Laval, 1050 avenue de la Médecine, Quebec City, QC, Canada, G1V 0A6. elizabeth.maunsell@fmed.ulaval.|Centre des Maladies du Sein Deschênes-Fabia, St-Sacrement Hospital, 1050 chemin Sainte-Foy, Québec City, QC, Canada, G1S 4L8. elizabeth.maunsell@fmed.ulaval.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Maunsell
authors.affiliation: Axe Oncologie, Centre de recherche du CHU de Québec-Université Laval, St-Sacrement Hospital, 1050 chemin Sainte-Foy, Quebec City, QC, Canada, G1S 4L8. Caroline.Diorio@crchudequebec.ulaval.ca.|Centre de recherche sur le cancer, Université Laval, St-Sacrement Hospital, 1050 chemin Sainte-Foy, Quebec City, QC, Canada, G1S 4L8. Caroline.Diorio@crchudequebec.ulaval.ca.|Département de médecine sociale et préventive, Faculté de médecine, Pavillon Ferdinand-Vandry, Loc 2428, Université Laval, 1050 avenue de la Médecine, Quebec City, QC, Canada, G1V 0A6. Caroline.Diorio@crchudequebec.ulaval.ca.|Centre des Maladies du Sein Deschênes-Fabia, St-Sacrement Hospital, 1050 chemin Sainte-Foy, Québec City, QC, Canada, G1S 4L8. Caroline.Diorio@crchudequebec.ulaval.ca.
authors.forename: Caroline
authors.initials: C
authors.lastname: Diorio
mesh_terms: D000728:Androgens / Q000097:blood*; D004967:Estrogens / Q000097:blood*; D005260:Female; D006801:Humans; D009043:Motor Activity; D016032:Randomized Controlled Trials as Topic
chemical_list: D000728:Androgens; D004967:Estrogens