title: The effect of vegetarian diets on iron status in adults: A systematic review and meta-analysis.
abstract: BACKGROUND
  Vegetarian diets exclude meat, seafood, and products containing these foods. Although the vegetarian lifestyle could lead to a better health status in adults, it may also bear risks for certain nutritional deficiencies. Cross-sectional studies and narrative reviews have shown that the iron status of vegetarians is compromised by the absence of highly bioavailable haem-iron in meatless diets and the inhibiting effect of certain components present in plant foods on non-haem iron bioavailability.
  
  
  METHODS
  The databases Pubmed, Scopus, Embase, and Cochrane CentralRegister of Controlled Trials were searched for studies comparing serum ferritin, as the major laboratory parameter for iron status of adult vegetarians with non-vegetarian control groups. A qualitative review was conducted as well as an inverse-variance random-effects meta-analysis to pool available data. In addition the effect of vegetarian diets according to gender was investigated with a subgroup analysis. The results were validated using a sensitivity analysis.
  
  
  RESULTS
  A total of 27 cross-sectional studies and three interventional studies were selected for the systematic review. The meta-analysis which combined data of 24 cross-sectional studies showed that adult vegetarians have significantly lower serum ferritin levels than their non-vegetarian controls (-29.71 µg/L, 95% CI [-39.69, -19.73], p < 0.01). Inclusion of semi-vegetarian diets did not change the results considerably (-23.27 µg/L, 95% CI [-29.77, -16.76], p < 0.01). The effects were more pronounced in men (-61.88 µg/L, 95% CI [-85.59, -38.17], p < 0.01) than in both premenopausal women (-17.70 μg/L, 95% CI [-29.80, -5.60], p < 0.01) and all women (-13.50 μg/L, 95% CI [-22.96, -4.04], p < 0.01), respectively.
  
  
  CONCLUSIONS
  In conclusion our results showed that vegetarians are more likely to have lower iron stores compared with non-vegetarians. However, since high iron stores are also a risk factor for certain non-communicable diseases, such as type 2 diabetes, it is recommended that not only vegetarians but also non-vegetarians should regularly control their iron status and improve their diet regarding the content and bioavailability of iron by consuming more plants and less meat.
authors.affiliation: a Department of Environmental Health , Center for Public Health, Medical University of Vienna , Vienna , Austria.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Haider
authors.affiliation: b Department of Epidemiology , German Institute of Human Nutrition , Nuthetal , Germany.
authors.forename: Lukas
authors.initials: L
authors.lastname: Schwingshackl
authors.affiliation: c Department of Nutritional Sciences , University of Vienna , Vienna , Austria.
authors.forename: Georg
authors.initials: G
authors.lastname: Hoffmann
authors.affiliation: a Department of Environmental Health , Center for Public Health, Medical University of Vienna , Vienna , Austria.
authors.forename: Cem
authors.initials: C
authors.lastname: Ekmekcioglu
mesh_terms: D000328:Adult; D014676:Diet, Vegetarian / Q000009:adverse effects*; D005293:Ferritins / Q000097:blood*; D006801:Humans; D007501:Iron / Q000008:administration & dosage*; D012307:Risk Factors
chemical_list: D005293:Ferritins; D007501:Iron
keywords: Vegetarian diets; ferritin; iron; iron status; meta-analysis; systematic review; vegan diet; vegetarians