Plant-based diets, including vegan diets, are associated with significant health benefits but can also increase the risk of certain nutritional deficiencies, particularly vitamin B12deficiency (Reference Bakaloudi, Halloran and Rippin1). Pregnant and lactating vegan women are at an even more elevated risk of B12 deficiency due to increased demand from the mother and foetus which, if not met(Reference Obeid, Murphy and Solé-Navais2), can have severe health implications across the life course(Reference Rogne, Tielemans and Chong3). We carried out a systematic review and meta-analysis to develop a consensus on vitamin B12 status among vegans and, more specifically, vegan women of childbearing age, using functional and static biomarkers.
A comprehensive search strategy of PubMed, Web of Science and Scopus was undertaken to identify studies comparing B12 Status among vegans versus non-vegan controls. After removing duplicates, two independent reviewers used Rayyan software to screen articles based on a comprehensive set of inclusion and exclusion criteria. Specific study characteristics and outcomes, including static - serum B12 & holotranscobalamin - and functional indicators of B12 status - concentrations of methylmalonic acid and/or homocysteine – of participants who supplemented with B12 were extracted. We conducted a random-effects meta-analysis framework for each outcome and undertook subgroup analyses to evaluate the influence of
B12 supplementation on B12 status among vegans.
A total of 1,894 records were identified. Only 13 studies were eligible and included in the systematic review & meta-analysis. Only one study provided gender-specific results for vitamin B12 status. Our meta-analysis of B12 status showed a significant trend towards lower serum B12 and holotranscobalamin concentrations (mean difference: -158 pmol/L | p = 0.05 & -13.1 pmol/L | p = 0.08, respectively) and higher methylmalonic acid and homocysteine (mean difference: +148 nmol/L | p = 0.01 & +3.76 umol/L | p = 0.03, respectively) among vegan participants compared to omnivores. Sub-group analysis showed significant, consistent, and physiologically relevant improvements in all B12 biomarkers between supplemented and non-supplemented vegan participants.
This is the first meta-analysis to highlight a significant and physiologically relevant decrease in vitamin
B12 status between vegans and non-vegans using static and functional biomarkers. Furthermore, the findings suggest that B12 supplementation can improve B12 status, as evidenced by both static and functional biomarkers of B12 status. Alarmingly, in light of B12 deficiency rates of 62% among pregnant vegetarian women (Reference Pawlak, Parrott and Raj4), only one study presented results for functional vitamin B12 status among vegan women of childbearing age. These findings underscore the importance of urgent research among this at-risk group, regularly monitoring B12 status and the need for appropriate use of B12 supplements among vegans, particularly those of child-bearing age. Further research is underway to explore the knowledge, attitudes and practices of B12 and supplementation among UK-dwelling vegan women of child-bearing age.
