Explaining the variability in recommended intake levels of folate, vitamin B12, iron and zinc for adults and elderly people

Recommended intake levels of micronutrients show considerable variation between European countries, causing confusion for policy-makers, health professionals, industry and consumers. We aim to explain the observed variability in recommended intake levels of folate, vitamin B12, iron and zinc for adults and elderly. Methods Recommended intake levels for men and women aged ≥18 years were extracted from nine reports including dietary reference values. We first critically reviewed current recommended intake levels and explored differences between reports and between subpopulations within reports. Methodological aspects and assumptions were compared between reports including the approach used, bioavailability factors, intra-individual variation (CV), reference weights, health indicators, cut-off levels indicating adequacy; and the evidence-base. Results Between reports, the ratio of highest to lowest recommended intake level was 2.0 for folate, vitamin B12 and zinc and 1.3 for iron. Within reports there were minor differences between recommended intake levels for younger and older adults. Recommended intake levels were mostly derived as the average nutrient requirement (ANR) + 2SD. For folate and vitamin B12, selected health indicators for estimating an ANR varied between reports and there was no consensus on criteria indicating adequacy. The observed variation in ANRs of iron and zinc was largely explained by differences in reference weights and bioavailability factors. Although for most micronutrients there were similarities in the consulted body of evidence, the evaluation and integration of evidence by experts was distinct. Conclusion For harmonizing recommended intake levels across Europe, addressed by Network of Excellence EURRECA, alignment and transparency of eminence-based decisions appears to be a key issue.