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 B 12 can elevate homocysteine. Vegetarians are a group of the population who are potentially at greater risk of vitamin B 12 deficiency than omnivores. This is the first systematic review and meta-analysis to appraise a range of studies that compared the homocysteine and vitamin B 12 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 B 12 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 B 12 did not differ from omnivores. The present study confirmed that an inverse relationship exists between plasma tHcy and serum vitamin B 12 , from which it can be concluded that the usual dietary source of vitamin B 12 is animal products and those who choose to omit or restrict these products are destined to become vitamin B 12 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.

The long-term health of vegetarians and vegans

“…Overall, these have shown that a wellplanned vegetarian or vegan diet can supply all the nutrients required for good health (6) . However, some concern remains over the possibility of low intakes of some nutrients such as vitamin B 12 , vitamin D, calcium and n-3 fatty acids in poorly selected and/or unfortified vegetarian or vegan diets (7,8) ; in particular, vitamin B 12 status has been widely observed to be relatively low in vegetarians and especially in vegans, and this is associated with relatively high plasma homocysteine (9) . Many studies have assessed health-related factors such as BMI, plasma cholesterol concentrations and blood pressure in vegetarians, but relatively few studies have been of sufficient magnitude and duration to examine the long-term health of vegetarians and vegans.…”

Analytical performance and method comparison study of the total homocysteine immunoassay on the AIA 600II analyser

“…Since homocysteine (Hcy) metabolism is catalysed by enzymes requiring B vitamins as cofactors, tHcy can also be considered a marker for folate and cobalamin deficiency [3,4].…”

Diet and Lifestyle Role in Homocysteine Metabolism in Turner Syndrome

“…Hyperhomocysteinemia is well established as an independent risk factor for coronary heart disease and arteriosclerosis. Studies have shown that coronary heart disease is linked to plasma Hcy levels, with a substantial risk occurring at > 10 μmol/L plasma Hcy; furthermore, each 5 μmol/L increase in plasma Hcy is associated with a 20% increased risk of coronary heart disease events [17]. The etiological factors for atherosclerosis raise conversion of methionine to Hcy thiolactone, which is the reactive cyclic internal lactone of Hcy, leading to a consequent thiolation reaction of amine-containing low-density lipoprotein.…”

“…It has been demonstrated that plasma tHcy levels correlate with the intake of animal source foods, the only natural abundant source of vitamin B 12 [17], while low intake of fruit and vegetables, natural folate sources, may be associated with inadequate folate intake [12, 25]. …”