Plasma total homocysteine status of vegetarians compared with omnivores: a systematic review and meta-analysis

Br J Nutr. 2013 Mar 14;109(5):785-94. doi: 10.1017/S000711451200520X. Epub 2013 Jan 8.

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.

Publication types

  • Comparative Study
  • Meta-Analysis
  • Review
  • Systematic Review

MeSH terms

  • Adult
  • Cohort Studies
  • Cross-Sectional Studies
  • Diet
  • Diet, Vegetarian / adverse effects*
  • Dietary Supplements
  • Female
  • Homocysteine / blood*
  • Humans
  • Hyperhomocysteinemia / etiology
  • Male
  • Middle Aged
  • Vitamin B 12 / administration & dosage
  • Vitamin B 12 / blood
  • Vitamin B 12 Deficiency / blood
  • Vitamin B 12 Deficiency / complications

Substances

  • Homocysteine
  • Vitamin B 12