Vitamin B 12 deficit is one of the most common vitamin deficiencies. However, there is no consensus on the cut-off points for vitamin B 12 and its co-markers, such as folate, holotranscobalamin, methylmalonic acid and homocysteine. In order to establish the state of the art about cut-off points used to determine vitamin B 12 deficiency in the last decades, the database MEDLINE was used for searching studies published in adults between December 1992 and May 2014 (69 articles), using search terms like 'vitamin B 12 ', 'cobalamin', 'cut-off', 'deficiency' alone or in combinations. Broad ranges of cut-off points for vitamin B 12 and its biomarkers were identified: vitamin B 12 ranged between 100 pmol/L and 350 pmol/L, holotranscobalamin 20-50 pmol/L, methylmalonic acid 0.210-0.470 μmol/L, homocysteine 10-21.6 μmol/L, serum folate 3.7-15.9 nmol/L and red blood cell 124-397 nmol/L. For the majority of studies, the potential influence of age, analytical methods, gender and fortified food consumption was not taken in account when choosing cut-off values. This could explain the discrepancies between studies on vitamin B 12 and folate deficiency prevalences. We conclude that there is inconsistency in the literature regarding vitamin B 12 cut-offs. It would be necessary to establish different reference cut-offs according to age, considering the analytical methods used.

There is a high prevalence of vitamin B deficiency and hyperhomocysteinemia in the studied population. Our data confirm the influence of these vitamins, especially folate, on tHcy levels, but hyperhomocysteinemia cannot be used as the only diagnostic criterion to detect subclinical vitamin deficiency in elderly people, especially to detect vitamin B12 deficiency.