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

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

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University of West London, School of Psychology, Social Work and Human Sciences, Paragon House, Boston Manor Road, Brentford, Middlesex TW8 9GA, UK.


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.

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