Aims: To systematically review the literature on daily losses and bioavailability of vitamin B12. These estimates could be used for deriving recommendations on vitamin B12 intake for adults and elderly. Methods: We identified publications on daily vitamin B12 losses (July 2011) and publications on the bioavailability of vitamin B12 from foods or diets (June 2010) in MEDLINE, EMBASE and the Cochrane Library. Results: A pooled analysis of five studies (52 subjects) showed that 0.13 ± 0.03% of the total body store is lost per day. Absorption of vitamin B12 ranged from 4.5 (dose of 38 µg from consumption of liver) to 83% (dose of 3.0 µg from consumption of mutton meat). Data from eight studies including 83 subjects suggested that the amount of vitamin B12 absorbed from food (Ai) increased with increasing doses of vitamin B12 (Di) as described by the equation: ln(Ai) = 0.7694 * ln(Di) - 0.9614. Conclusion: Daily vitamin B12 losses in apparently healthy adults and elderly probably range from 1.4 to 5.1 µg. Vitamin B12 intakes needed to compensate for these losses seem to range from 3.8 to 20.7 µg. More evidence is needed on the relationships between biochemical markers of vitamin B12 status, vitamin B12 body store and long-term health outcomes to evaluate whether current recommendations on vitamin B12 intake (1.4-3 µg) need to be changed.

Current recommendations on vitamin B₁₂ intake vary from 1.4 to 3.0 μg per day and are based on the amount needed for maintenance of hematologic status or on the amount needed to compensate obligatory losses. This systematic review evaluates whether the relation between vitamin B₁₂ intake and cognitive function should be considered for underpinning vitamin B₁₂ recommendations in the future. The authors summarized dose-response evidence from randomized controlled trials and prospective cohort studies on the relation of vitamin B₁₂ intake and status with cognitive function in adults and elderly people. Two randomized controlled trials and 6 cohort studies showed no association or inconsistent associations between vitamin B₁₂ intake and cognitive function. Random-effects meta-analysis showed that serum/plasma vitamin B₁₂ (50 pmol/L) was not associated with risk of dementia (4 cohort studies), global cognition z scores (4 cohort studies), or memory z scores (4 cohort studies). Although dose-response evidence on sensitive markers of vitamin B₁₂ status (methylmalonic acid and holotranscobalamin) was scarce, 4 of 5 cohort studies reported significant associations with risk of dementia, Alzheimer's disease, or global cognition. Current evidence on the relation between vitamin B₁₂ intake or status and cognitive function is not sufficient for consideration in the development of vitamin B₁₂ recommendations. Further studies should consider the selection of sensitive markers of vitamin B₁₂ status.

Objective: To signal key issues for harmonising approaches for establishing micronutrient recommendations by explaining observed variation in recommended intakes of folate, vitamin B₁₂, Fe and Zn for adults and elderly people.Design: We explored differences in recommended intakes of folate, vitamin B₁₂, Fe and Zn for adults between nine reports on micronutrient recommendations. Approaches used for setting recommendations were compared as well as eminence-based decisions regarding the selection of health indicators indicating adequacy of intakes and the consulted evidence base.Results: In nearly all reports, recommendations were based on the average nutrient requirement. Variation in recommended folate intakes (200–400 μg/d) was related to differences in the consulted evidence base, whereas variation in vitamin B₁₂recommendations (1·4–3·0 μg/d) was due to the selection of different CV (10–20 %) and health indicators (maintenance of haematological status or basal losses). Variation in recommended Fe intakes (men 8–10 mg/d, premenopausal women 14·8–19·6 mg/d, postmenopausal women 7·5–10·0 mg/d) was explained by different assumed reference weights and bioavailability factors (10–18 %). Variation in Zn recommendations (men 7–14 mg/d, women 4·9–9·0 mg/d) was also explained by different bioavailability factors (24–48 %) as well as differences in the consulted evidence base.Conclusions: For the harmonisation of approaches for setting recommended intakes of folate, vitamin B₁₂, Fe and Zn across European countries, standardised methods are needed to (i) select health indicators and define adequate biomarker concentrations, (ii) make assumptions about inter-individual variation in requirements, (iii) derive bioavailability factors and (iv) collate, select, interpret and integrate evidence on requirements.