title: Subnormal vitamin B12 concentrations and anaemia in older people: a systematic review.
abstract: BACKGROUND
  Pernicious anaemia is undeniably associated with vitamin B12 deficiency, but the association between subnormal vitamin B12 concentrations and anaemia in older people is unclear. The aim of this systematic review was to evaluate the association between subnormal vitamin B12 concentrations and anaemia in older people.
  
  
  METHODS
  Clinical queries for aetiology and treatment in bibliographic databases (PubMed [01/1949-10/2009]; EMBASE [01/1980-10/2009]) were used. Reference lists were checked for additional relevant studies. Observational studies (> or =50 participants) and randomized placebo-controlled intervention trials (RCTs) were considered.
  
  
  RESULTS
  25 studies met the inclusion criteria. Twenty-one observational cross-sectional studies (total number of participants n = 16185) showed inconsistent results. In one longitudinal observational study, low vitamin B12 concentrations were not associated with an increased risk of anaemia (total n = 423). The 3 RCTs (total n = 210) were well-designed and showed no effect of vitamin B12 supplementation on haemoglobin concentrations during follow-up in subjects with subnormal vitamin B12 concentrations at the start of the study. Due to large clinical and methodological heterogeneity, statistical pooling of data was not performed.
  
  
  CONCLUSIONS
  Evidence of a positive association between a subnormal serum vitamin B12 concentration and anaemia in older people is limited and inconclusive. Further well-designed studies are needed to determine whether subnormal vitamin B12 is a risk factor for anaemia in older people.
authors.affiliation: Department of Public Health and Primary Care, Leiden University Medical Center, Leiden, The Netherlands. w.p.j.den_elzen@lumc.nl
authors.forename: Wendy P J
authors.initials: WP
authors.lastname: den Elzen
authors.forename: Gerda M
authors.initials: GM
authors.lastname: van der Weele
authors.forename: Jacobijn
authors.initials: J
authors.lastname: Gussekloo
authors.forename: Rudi G J
authors.initials: RG
authors.lastname: Westendorp
authors.forename: Willem J J
authors.initials: WJ
authors.lastname: Assendelft
mesh_terms: D000367:Age Factors; D000368:Aged; D003430:Cross-Sectional Studies; D003704:Dementia / Q000097:blood* / Q000453:epidemiology* / Q000209:etiology; D006801:Humans; D008137:Longitudinal Studies; D016032:Randomized Controlled Trials as Topic / Q000379:methods; D014805:Vitamin B 12 / Q000097:blood*; D014806:Vitamin B 12 Deficiency / Q000097:blood* / Q000150:complications / Q000453:epidemiology*
chemical_list: D014805:Vitamin B 12