title: Plasma total homocysteine status of vegetarians compared with omnivores: a systematic review and meta-analysis.
abstract: There is strong evidence indicating that elevated plasma total homocysteine (tHcy) levels are a major independent biomarker and/or a contributor to chronic conditions, such as CVD. A deficiency of vitamin B₁₂ can elevate homocysteine. Vegetarians are a group of the population who are potentially at greater risk of vitamin B₁₂ deficiency than omnivores. This is the first systematic review and meta-analysis to appraise a range of studies that compared the homocysteine and vitamin B₁₂ levels of vegetarians and omnivores. The search methods employed identified 443 entries, from which, by screening using set inclusion and exclusion criteria, six eligible cohort case studies and eleven cross-sectional studies from 1999 to 2010 were revealed, which compared concentrations of plasma tHcy and serum vitamin B₁₂ of omnivores, lactovegetarians or lacto-ovovegetarians and vegans. Of the identified seventeen studies (3230 participants), only two studies reported that vegan concentrations of plasma tHcy and serum vitamin B₁₂ did not differ from omnivores. The present study confirmed that an inverse relationship exists between plasma tHcy and serum vitamin B₁₂, from which it can be concluded that the usual dietary source of vitamin B₁₂ is animal products and those who choose to omit or restrict these products are destined to become vitamin B₁₂ deficient. At present, the available supplement, which is usually used for fortification of food, is the unreliable cyanocobalamin. A well-designed study is needed to investigate a reliable and suitable supplement to normalise the elevated plasma tHcy of a high majority of vegetarians. This would fill the gaps in the present nutritional scientific knowledge.
authors.affiliation: University of West London, School of Psychology, Social Work and Human Sciences, Paragon House, Boston Manor Road, Brentford, Middlesex              TW8 9GA, UK.
authors.forename: Derek
authors.initials: D
authors.lastname: Obersby
authors.forename: David C
authors.initials: DC
authors.lastname: Chappell
authors.forename: Andrew
authors.initials: A
authors.lastname: Dunnett
authors.forename: Amalia A
authors.initials: AA
authors.lastname: Tsiami
mesh_terms: D000328:Adult; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D004032:Diet; D014676:Diet, Vegetarian / Q000009:adverse effects*; D019587:Dietary Supplements; D005260:Female; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D020138:Hyperhomocysteinemia / Q000209:etiology; D008297:Male; D008875:Middle Aged; D014805:Vitamin B 12 / Q000008:administration & dosage / Q000097:blood; D014806:Vitamin B 12 Deficiency / Q000097:blood / Q000150:complications
chemical_list: D006710:Homocysteine; D014805:Vitamin B 12