title: Arachidonic acid and cancer risk: a systematic review of observational studies.
abstract: BACKGROUND
  An n-6 essential fatty acid, arachidonic acid (ARA) is converted into prostaglandin E2, which is involved in tumour extension. However, it is unclear whether dietary ARA intake leads to cancer in humans. We thus systematically evaluated available observational studies on the relationship between ARA exposure and the risk of colorectal, skin, breast, prostate, lung, and stomach cancers.
  
  
  METHODS
  We searched the PubMed database for articles published up to May 17, 2010. 126 potentially relevant articles from the initial search and 49,670 bibliographies were scrutinised to identify eligible publications by using predefined inclusion criteria. A comprehensive literature search yielded 52 eligible articles, and their reporting quality and methodological quality was assessed. Information on the strength of the association between ARA exposure and cancer risk, the dose-response relationship, and methodological limitations was collected and evaluated with respect to consistency and study design.
  
  
  RESULTS
  For colorectal, skin, breast, and prostate cancer, 17, 3, 18, and 16 studies, respectively, were identified. We could not obtain eligible reports for lung and stomach cancer. Studies used cohort (n = 4), nested case-control (n = 12), case-control (n = 26), and cross-sectional (n = 12) designs. The number of subjects (n = 15 - 88,795), ARA exposure assessment method (dietary intake or biomarker), cancer diagnosis and patient recruitment procedure (histological diagnosis, cancer registries, or self-reported information) varied among studies. The relationship between ARA exposure and colorectal cancer was inconsistent based on ARA exposure assessment methodology (dietary intake or biomarker). Conversely, there was no strong positive association or dose-response relationship for breast or prostate cancer. There were limited numbers of studies on skin cancer to draw any conclusions from the results.
  
  
  CONCLUSIONS
  The available epidemiologic evidence is weak because of the limited number of studies and their methodological limitations, but nonetheless, the results suggest that ARA exposure is not associated with increased breast and prostate cancer risk. Further evidence from well-designed observational studies is required to confirm or refute the association between ARA exposure and risk of cancer.
authors.affiliation: Department of Social and Preventive Epidemiology, School of Public Health, The University of Tokyo, Tokyo, Japan. Mai_Sakai@suntory.co.jp
authors.forename: Mai
authors.initials: M
authors.lastname: Sakai
authors.forename: Saki
authors.initials: S
authors.lastname: Kakutani
authors.forename: Chika
authors.initials: C
authors.lastname: Horikawa
authors.forename: Hisanori
authors.initials: H
authors.lastname: Tokuda
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kawashima
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Shibata
authors.forename: Hitomi
authors.initials: H
authors.lastname: Okubo
authors.forename: Satoshi
authors.initials: S
authors.lastname: Sasaki
mesh_terms: D016718:Arachidonic Acid / Q000009:adverse effects* / Q000032:analysis; D001943:Breast Neoplasms / Q000139:chemically induced; D015179:Colorectal Neoplasms / Q000139:chemically induced; D004032:Diet / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008297:Male; D009369:Neoplasms / Q000139:chemically induced*; D011471:Prostatic Neoplasms / Q000139:chemically induced; D012307:Risk Factors; D012878:Skin Neoplasms / Q000139:chemically induced
chemical_list: D016718:Arachidonic Acid