title: Obesity and cancer: the role of vitamin D.
abstract: BACKGROUND
  It is estimated that 20% of all cancer cases are caused by obesity. Vitamin D is thought to be one of the mechanisms underlying this association. This review aims to summarise the evidence for the mediating effect of vitamin D on the link between obesity and cancer.
  
  
  METHODS
  Three literature searches using PubMed and Embase were conducted to assess whether vitamin D plays an important role in the pathway between obesity and cancer: (1) obesity and cancer; (2) obesity and vitamin D; and (3) vitamin D and cancer. A systematic review was performed for (1) and (3), whereas a meta-analysis including random effects analyses was performed for (2).
  
  
  RESULTS
  (1) 32 meta-analyses on obesity and cancer were identified; the majority reported a positive association between obesity and risk of cancer. (2) Our meta-analysis included 12 original studies showing a pooled relative risk of 1.52 (95% CI: 1.33-1.73) for risk of vitamin D deficiency (<50 nmol/L) in obese people (body mass index>30 kg/m2). (3) 21 meta-analyses on circulating vitamin D levels and cancer risk were identified with different results for different types of cancer.
  
  
  CONCLUSIONS
  There is consistent evidence for a link between obesity and cancer as well as obesity and low vitamin D. However, it seems like the significance of the mediating role of vitamin D in the biological pathways linking obesity and cancer is low. There is a need for a study including all three components while dealing with bias related to dietary supplements and vitamin D receptor polymorphisms.
authors.affiliation: King's College London, School of Medicine, Division of Cancer Studies, Cancer Epidemiology Group, London, UK. thurkaa.t.shanmugalingam@kcl.ac.uk.
authors.forename: Thurkaa
authors.initials: T
authors.lastname: Shanmugalingam
authors.forename: Danielle
authors.initials: D
authors.lastname: Crawley
authors.forename: Cecilia
authors.initials: C
authors.lastname: Bosco
authors.forename: Jennifer
authors.initials: J
authors.lastname: Melvin
authors.forename: Sabine
authors.initials: S
authors.lastname: Rohrmann
authors.forename: Simon
authors.initials: S
authors.lastname: Chowdhury
authors.forename: Lars
authors.initials: L
authors.lastname: Holmberg
authors.forename: Mieke
authors.initials: M
authors.lastname: Van Hemelrijck
mesh_terms: D005260:Female; D006801:Humans; D008297:Male; D009369:Neoplasms / Q000453:epidemiology / Q000378:metabolism*; D009765:Obesity / Q000453:epidemiology / Q000378:metabolism*; D016017:Odds Ratio; D012306:Risk; D014807:Vitamin D / Q000378:metabolism*
chemical_list: D014807:Vitamin D