Green, R. & Miller, J. W. in Handbook of Vitamins 5th edn (eds Zempleni, J. et al.) 447–489 (Taylor & Francis, 2014). A comprehensive review of B12 biochemistry, nutrition and metabolism.
Nielsen, M. J. et al. Vitamin B12 transport from food to the body's cells — a sophisticated, multistep pathway. Nat. Rev. Gastroenterol. Hepatol. 9, 345–354 (2012). A thorough review of B12 absorption, cellular uptake and intracellular metabolism in health and disease.
Allen, L. H. How common is vitamin B-12 deficiency? Am. J. Clin. Nutr. 89, 693S–696S (2009).
Stabler, S. P. Clinical practice. Vitamin B12 deficiency. N. Engl. J. Med. 368, 149–160 (2013). An authoritative review of B12 deficiency from the clinical perspective.
Green, R. Vitamin B12 deficiency from the perspective of a practicing hematologist. Blood 129, 2603–2611 (2017). A recent and authoritative up-to-date summary of the clinical aspects of B12 deficiency with emphasis on the haematological perspective.
Lindenbaum, J. et al. Neuropsychiatric disorders caused by cobalamin deficiency in the absence of anemia or macrocytosis. N. Engl. J. Med. 318, 1720–1728 (1988).
Carmel, R. Subtle and atypical cobalamin deficiency states. Am. J. Hematol. 34, 108–114 (1990).
Green, R. Metabolite assays in cobalamin and folate deficiency. Baillieres Clin. Haematol. 8, 533–566 (1995).
Green, R. Screening for vitamin B12 deficiency: caveat emptor. Ann. Intern. Med. 124, 509–511 (1996).
Carmel, R. Subclinical cobalamin deficiency. Curr. Opin. Gastroenterol. 28, 151–158 (2012). A detailed description of the puzzling but common entity of B12 inadequacy without frank manifestations of deficiency.
Carmel, R. Cobalamin, the stomach, and aging. Am. J. Clin. Nutr. 66, 750–759 (1997).
Carmel, R. & Sarrai, M. Diagnosis and management of clinical and subclinical cobalamin deficiency: advances and controversies. Curr. Hematol. Rep. 5, 23–33 (2006).
Carmel, R. et al. Update on cobalamin, folate, and homocysteine. Hematology Am. Soc. Hematol. Educ. Program 2003, 62–81 (2003).
Carmel, R. Prevalence of undiagnosed pernicious anemia in the elderly. Arch. Intern. Med. 156, 1097–1100 (1996).
Yajnik, C. S. et al. Vitamin B12 deficiency and hyperhomocysteinemia in rural and urban Indians. J. Assoc. Physicians India 54, 775–782 (2006).
Premkumar, M. et al. Cobalamin and folic acid status in relation to the etiopathogenesis of pancytopenia in adults at a tertiary care centre in north India. Anemia 2012, 707402 (2012).
James, J. S. Low vitamin B-12 blood levels associated with faster progression to AIDS. AIDS Treat. News 264, 3–4 (1997).
Allen, L. H. Causes of vitamin B12 and folate deficiency. Food Nutr. Bull. 29 (Suppl. 2), S20–S34 (2008).
Bailey, R. L. et al. Monitoring of vitamin B-12 nutritional status in the United States by using plasma methylmalonic acid and serum vitamin B-12. Am. J. Clin. Nutr. 94, 552–561 (2011).
Yang, Q. et al. Folic acid source, usual intake, and folate and vitamin B-12 status in US adults: National Health and Nutrition Examination Survey (NHANES) 2003–2006. Am. J. Clin. Nutr. 91, 64–72 (2010).
Pennypacker, L. C. et al. High prevalence of cobalamin deficiency in elderly outpatients. J. Am. Geriatr. Soc. 40, 1197–1204 (1992).
Clarke, R. et al. Vitamin B12 and folate deficiency in later life. Age Ageing 33, 34–41 (2004).
Carmel, R. et al. Serum cobalamin, homocysteine, and methylmalonic acid concentrations in a multiethnic elderly population: ethnic and sex differences in cobalamin and metabolite abnormalities. Am. J. Clin. Nutr. 70, 904–910 (1999).
Stabler, S. P., Lindenbaum, J. & Allen, R. H. Vitamin B-12 deficiency in the elderly: current dilemmas. Am. J. Clin. Nutr. 66, 741–749 (1997).
Naurath, H. J. et al. Effects of vitamin B12, folate, and vitamin B6 supplements in elderly people with normal serum vitamin concentrations. Lancet 346, 85–89 (1995).
van Asselt, D. Z. et al. Cobalamin-binding proteins in normal and cobalamin-deficient older subjects. Ann. Clin. Biochem. 40, 65–69 (2003).
Johnson, M. A. et al. Vitamin B12 deficiency in African American and white octogenarians and centenarians in Georgia. J. Nutr. Health Aging 14, 339–345 (2010).
Murphy, M. M. et al. Longitudinal study of the effect of pregnancy on maternal and fetal cobalamin status in healthy women and their offspring. J. Nutr. 137, 1863–1867 (2007).
Greibe, E. et al. Uptake of cobalamin and markers of cobalamin status: a longitudinal study of healthy pregnant women. Clin. Chem. Lab Med. 49, 1877–1882 (2011).
Milman, N. et al. Cobalamin status during normal pregnancy and postpartum: a longitudinal study comprising 406 Danish women. Eur. J. Haematol. 76, 521–525 (2006).
Bae, S. et al. Vitamin B-12 status differs among pregnant, lactating, and control women with equivalent nutrient intakes. J. Nutr. 145, 1507–1514 (2015).
Obeid, R. et al. The cobalamin-binding proteins transcobalamin and haptocorrin in maternal and cord blood sera at birth. Clin. Chem. 52, 263–269 (2006).
McLean, E., de Benoist, B. & Allen, L. H. Review of the magnitude of folate and vitamin B12 deficiencies worldwide. Food Nutr. Bull. 29 (Suppl. 2), S38–S51 (2008).
Barnabe, A. et al. Folate, vitamin B12 and homocysteine status in the post-folic acid fortification era in different subgroups of the Brazilian population attended to at a public health care center. Nutr. J. 14, 19 (2015).
Yusufji, D., Mathan, V. I. & Baker, S. J. Iron, folate, and vitamin B12 nutrition in pregnancy: a study of 1 000 women from southern India. Bull. World Health Organ. 48, 15–22 (1973).
Koc, A. et al. High frequency of maternal vitamin B12 deficiency as an important cause of infantile vitamin B12 deficiency in Sanliurfa province of Turkey. Eur. J. Nutr. 45, 291–297 (2006).
Yajnik, C. S. et al. Vitamin B12 and folate concentrations during pregnancy and insulin resistance in the offspring: the Pune Maternal Nutrition Study. Diabetologia 51, 29–38 (2008).
Tucker, K. L. et al. Plasma vitamin B-12 concentrations relate to intake source in the Framingham Offspring study. Am. J. Clin. Nutr. 71, 514–522 (2000).
Monsen, A. L. et al. Cobalamin status and its biochemical markers methylmalonic acid and homocysteine in different age groups from 4 days to 19 years. Clin. Chem. 49, 2067–2075 (2003).
Fokkema, M. R. et al. Plasma total homocysteine increases from day 20 to 40 in breastfed but not formula-fed low-birthweight infants. Acta Paediatr. 91, 507–511 (2002).
Greibe, E. et al. Cobalamin and haptocorrin in human milk and cobalamin-related variables in mother and child: a 9-mo longitudinal study. Am. J. Clin. Nutr. 98, 389–395 (2013).
Molloy, A. M. et al. Effects of folate and vitamin B12 deficiencies during pregnancy on fetal, infant, and child development. Food Nutr. Bull. 29 (Suppl. 2), S101–S111 (2008).
Bjorke-Monsen, A. L. et al. Common metabolic profile in infants indicating impaired cobalamin status responds to cobalamin supplementation. Pediatrics 122, 83–91 (2008).
Hay, G. et al. Folate and cobalamin status in relation to breastfeeding and weaning in healthy infants. Am. J. Clin. Nutr. 88, 105–114 (2008).
Torsvik, I. et al. Cobalamin supplementation improves motor development and regurgitations in infants: results from a randomized intervention study. Am. J. Clin. Nutr. 98, 1233–1240 (2013).
Cobayashi, F. et al. Genetic and environmental factors associated with vitamin B12 status in Amazonian children. Public Health Nutr. 18, 2202–2210 (2015).
Hine, B. et al. Transcobalamin derived from bovine milk stimulates apical uptake of vitamin B12 into human intestinal epithelial cells. J. Cell. Biochem. 115, 1948–1954 (2014).
Chanarin, I. Cobalamins and nitrous oxide: a review. J. Clin. Pathol. 33, 909–916 (1980).
Green, R. & Kinsella, L. J. Current concepts in the diagnosis of cobalamin deficiency. Neurology 45, 1435–1440 (1995).
O’Leary, P. W., Combs, M. J. & Schilling, R. F. Synergistic deleterious effects of nitrous oxide exposure and vitamin B12 deficiency. J. Lab. Clin. Med. 105, 428–431 (1985).
Toh, B. H., van Driel, I. R. & Gleeson, P. A. Pernicious anemia. N. Engl. J. Med. 337, 1441–1448 (1997). A landmark paper on the clinical and immunological basis of the disease that is the essential paradigm of B12 deficiency and its immunological basis.
Hershko, C. et al. Variable hematologic presentation of autoimmune gastritis: age-related progression from iron deficiency to cobalamin depletion. Blood 107, 1673–1679 (2006).
Amedei, A. et al. Molecular mimicry between Helicobacter pylori antigens and H+, K+ — adenosine triphosphatase in human gastric autoimmunity. J. Exp. Med. 198, 1147–1156 (2003).
Doscherholmen, A., McMahon, J. & Ripley, D. Vitamin B12 assimilation from chicken meat. Am. J. Clin. Nutr. 31, 825–830 (1978).
Bellou, A. et al. Cobalamin deficiency with megaloblastic anaemia in one patient under long-term omeprazole therapy. J. Intern. Med. 240, 161–164 (1996).
Lam, J. R. et al. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA 310, 2435–2442 (2013).
Degnan, P. H., Taga, M. E. & Goodman, A. L. Vitamin B12 as a modulator of gut microbial ecology. Cell Metab. 20, 769–778 (2014).
Fedosov, S. N. et al. Mechanisms of discrimination between cobalamins and their natural analogues during their binding to the specific B12-transporting proteins. Biochemistry 46, 6446–6458 (2007).
Tanwar, V. S. et al. Common variant in FUT2 gene is associated with levels of vitamin B12 in Indian population. Gene 515, 224–228 (2013).
Kelly, R. J. et al. Sequence and expression of a candidate for the human Secretor blood group alpha(1,2)fucosyltransferase gene (FUT2). Homozygosity for an enzyme-inactivating nonsense mutation commonly correlates with the non-secretor phenotype. J. Biol. Chem. 270, 4640–4649 (1995).
Hazra, A. et al. Common variants of FUT2 are associated with plasma vitamin B12 levels. Nat. Genet. 40, 1160–1162 (2008).
Tanaka, T. et al. Genome-wide association study of vitamin B6, vitamin B12, folate, and homocysteine blood concentrations. Am. J. Hum. Genet. 84, 477–482 (2009).
Jensen, L. L. et al. Lack of megalin expression in adult human terminal ileum suggests megalin-independent cubilin/amnionless activity during vitamin B12 absorption. Physiol. Rep. 2, e12086 (2014).
Beedholm-Ebsen, R. et al. Identification of multidrug resistance protein 1 (MRP1/ABCC1) as a molecular gate for cellular export of cobalamin. Blood 115, 1632–1639 (2010).
Aminoff, M. et al. Mutations in CUBN, encoding the intrinsic factor-vitamin B12 receptor, cubilin, cause hereditary megaloblastic anaemia 1. Nat. Genet. 21, 309–313 (1999).
Tanner, S. M. et al. Amnionless, essential for mouse gastrulation, is mutated in recessive hereditary megaloblastic anemia. Nat. Genet. 33, 426–429 (2003).
Gueant, J. L. et al. Decreased activity of intestinal and urinary intrinsic factor receptor in Grasbeck-Imerslund disease. Gastroenterology 108, 1622–1628 (1995).
Quadros, E. V. & Sequeira, J. M. Cellular uptake of cobalamin: transcobalamin and the TCblR/CD320 receptor. Biochimie 95, 1008–1018 (2013).
Gherasim, C., Lofgren, M. & Banerjee, R. Navigating the B12 road: assimilation, delivery, and disorders of cobalamin. J. Biol. Chem. 288, 13186–13193 (2013). An in-depth review of the fascinating molecular ensemble that is involved in the handling of this precious micronutrient in genetically normal and mutated cells.
Froese, D. S. & Gravel, R. A. Genetic disorders of vitamin B12 metabolism: eight complementation groups — eight genes. Expert Rev. Mol. Med. 12, e37 (2010). A well-illustrated, concise but complete summary of the eight recognized inborn errors of B12 metabolism that uses the ‘experiments of nature’ to explain the complex network of intracellular pathways involved in B12 processing.
Whitehead, V. M. Acquired and inherited disorders of cobalamin and folate in children. Br. J. Haematol. 134, 125–136 (2006).
Trakadis, Y. J. et al. Update on transcobalamin deficiency: clinical presentation, treatment and outcome. J. Inherit. Metab. Dis. 37, 461–473 (2014).
Miller, J. W. et al. Transcobalamin II 775G>C polymorphism and indices of vitamin B12 status in healthy older adults. Blood 100, 718–720 (2002).
Namour, F. et al. Transcobalamin codon 259 polymorphism in HT-29 and Caco-2 cells and in Caucasians: relation to transcobalamin and homocysteine concentration in blood. Blood 97, 1092–1098 (2001).
Watkins, D. & Rosenblatt, D. S. Lessons in biology from patients with inborn errors of vitamin B12 metabolism. Biochimie 95, 1019–1022 (2013).
Sharma, G. S., Kumar, T. & Singh, L. R. N-homocysteinylation induces different structural and functional consequences on acidic and basic proteins. PLoS ONE 9, e116386 (2014).
Ghemrawi, R. et al. Decreased vitamin B12 availability induces ER stress through impaired SIRT1-deacetylation of HSF1. Cell Death Dis. 4, e553 (2013).
Hannibal, L., DiBello, P. M. & Jacobsen, D. W. Proteomics of vitamin B12 processing. Clin. Chem. Lab. Med. 51, 477–488 (2013).
Richard, E. et al. Oxidative stress and apoptosis in homocystinuria patients with genetic remethylation defects. J. Cell. Biochem. 114, 183–191 (2013).
Peracchi, M. et al. Human cobalamin deficiency: alterations in serum tumour necrosis factor-alpha and epidermal growth factor. Eur. J. Haematol. 67, 123–127 (2001).
Scalabrino, G. et al. High tumor necrosis factor-alpha levels in cerebrospinal fluid of cobalamin-deficient patients. Ann. Neurol. 56, 886–890 (2004).
Caterino, M. et al. The proteome of cblC defect: in vivo elucidation of altered cellular pathways in humans. J. Inherit. Metab. Dis. 38, 969–979 (2015).
Troen, A. M. et al. B-vitamin deficiency causes hyperhomocysteinemia and vascular cognitive impairment in mice. Proc. Natl Acad. Sci. USA 105, 12474–12479 (2008).
Fuso, A. & Scarpa, S. One-carbon metabolism and Alzheimer's disease: is it all a methylation matter? Neurobiol. Aging 32, 1192–1195 (2011).
Scalabrino, G. The multi-faceted basis of vitamin B12 (cobalamin) neurotrophism in adult central nervous system: lessons learned from its deficiency. Prog. Neurobiol. 88, 203–220 (2009).
Battaglia-Hsu, S. F. et al. Vitamin B12 deficiency reduces proliferation and promotes differentiation of neuroblastoma cells and up-regulates PP2A, proNGF, and TACE. Proc. Natl Acad. Sci. USA 106, 21930–21935 (2009).
Rosenblatt, D. S. & Whitehead, V. M. Cobalamin and folate deficiency: acquired and hereditary disorders in children. Semin. Hematol. 36, 19–34 (1999).
Dror, D. K. & Allen, L. H. Effect of vitamin B12 deficiency on neurodevelopment in infants: current knowledge and possible mechanisms. Nutr. Rev. 66, 250–255 (2008).
Demir, N. et al. Clinical and neurological findings of severe vitamin B12 deficiency in infancy and importance of early diagnosis and treatment. J. Paediatr. Child Health 49, 820–824 (2013).
Copp, A. J. et al. Spina bifida. Nat. Rev. Dis. Primers 1, 15007 (2015).
Molloy, A. M. et al. Maternal vitamin B12 status and risk of neural tube defects in a population with high neural tube defect prevalence and no folic acid fortification. Pediatrics 123, 917–923 (2009).
Suarez, L. et al. Maternal serum B12 levels and risk for neural tube defects in a Texas–Mexico border population. Ann. Epidemiol. 13, 81–88 (2003).
Green, R. & Miller, J. W. Vitamin B12 deficiency is the dominant nutritional cause of hyperhomocysteinemia in a folic acid-fortified population. Clin. Chem. Lab. Med. 43, 1048–1051 (2005).
Smith, A. D. et al. Homocysteine-lowering by B vitamins slows the rate of accelerated brain atrophy in mild cognitive impairment: a randomized controlled trial. PLoS ONE 5, e12244 (2010).
de Jager, C. A. et al. Cognitive and clinical outcomes of homocysteine-lowering B-vitamin treatment in mild cognitive impairment: a randomized controlled trial. Int. J. Geriatr. Psychiatry 27, 592–600 (2012).
Douaud, G. et al. Preventing Alzheimer's disease-related gray matter atrophy by B-vitamin treatment. Proc. Natl Acad. Sci. USA 110, 9523–9528 (2013).
Haan, M. N. et al. Homocysteine, B vitamins, and the incidence of dementia and cognitive impairment: results from the Sacramento Area Latino Study on Aging. Am. J. Clin. Nutr. 85, 511–517 (2007).
Morris, M. S. et al. Folate and vitamin B-12 status in relation to anemia, macrocytosis, and cognitive impairment in older Americans in the age of folic acid fortification. Am. J. Clin. Nutr. 85, 193–200 (2007).
Brito, A. et al. Vitamin B-12 treatment of asymptomatic, deficient, elderly Chileans improves conductivity in myelinated peripheral nerves, but high serum folate impairs vitamin B-12 status response assessed by the combined indicator of vitamin B-12 status. Am. J. Clin. Nutr. 103, 250–257 (2016).
Chhabra, N., Lee, S. & Sakalis, E. G. Cobalamin deficiency causing severe hemolytic anemia: a pernicious presentation. Am. J. Med. 128, e5–e6 (2015).
Parmentier, S. et al. Severe pernicious anemia with distinct cytogenetic and flow cytometric aberrations mimicking myelodysplastic syndrome. Ann. Hematol. 91, 1979–1981 (2012).
Andres, E. et al. Current hematological findings in cobalamin deficiency. A study of 201 consecutive patients with documented cobalamin deficiency. Clin. Lab. Haematol. 28, 50–56 (2006).
Green, R. Anemias beyond B12 and iron deficiency: the buzz about other B's, elementary, and nonelementary problems. Hematology Am. Soc. Hematol. Educ. Program 2012, 492–498 (2012).
Devalia, V., Hamilton, M. S. & Molloy, A. M. Guidelines for the diagnosis and treatment of cobalamin and folate disorders. Br. J. Haematol. 166, 496–513 (2014).
Lindenbaum, J. et al. Diagnosis of cobalamin deficiency: II. Relative sensitivities of serum cobalamin, methylmalonic acid, and total homocysteine concentrations. Am. J. Hematol. 34, 99–107 (1990).
Fedosov, S. N. et al. Combined indicator of vitamin B12 status: modification for missing biomarkers and folate status and recommendations for revised cut-points. Clin. Chem. Lab. Med. 53, 1215–1225 (2015).
Carmel, R. & Agrawal, Y. P. Failures of cobalamin assays in pernicious anemia. N. Engl. J. Med. 367, 385–386 (2012).
Nexo, E. Variation with age of reference values for P-cobalamins. Scand. J. Haematol. 30, 430–432 (1983).
Arendt, J. F. & Nexo, E. Unexpected high plasma cobalamin: proposal for a diagnostic strategy. Clin. Chem. Lab. Med. 51, 489–496 (2013).
Herzlich, B. & Herbert, V. Depletion of serum holotranscobalamin II. An early sign of negative vitamin B12 balance. Lab. Invest. 58, 332–337 (1988).
Risch, M. et al. Vitamin B12 and folate levels in healthy Swiss senior citizens: a prospective study evaluating reference intervals and decision limits. BMC Geriatr. 15, 82 (2015).
Miller, J. W. et al. Measurement of total vitamin B12 and holotranscobalamin, singly and in combination, in screening for metabolic vitamin B12 deficiency. Clin. Chem. 52, 278–285 (2006).
Nexo, E. & Hoffmann-Lucke, E. Holotranscobalamin, a marker of vitamin B-12 status: analytical aspects and clinical utility. Am. J. Clin. Nutr. 94, 359S–365S (2011).
Refsum, H. et al. Facts and recommendations about total homocysteine determinations: an expert opinion. Clin. Chem. 50, 3–32 (2004).
Rasmussen, K. et al. Age- and gender-specific reference intervals for total homocysteine and methylmalonic acid in plasma before and after vitamin supplementation. Clin. Chem. 42, 630–636 (1996).
Vogiatzoglou, A. et al. Determinants of plasma methylmalonic acid in a large population: implications for assessment of vitamin B12 status. Clin. Chem. 55, 2198–2206 (2009).
Molloy, A. M. et al. A common polymorphism in HIBCH influences methylmalonic acid concentrations in blood independently of cobalamin. Am. J. Hum. Genet. 98, 869–882 (2016).
Hvas, A. M. & Nexo, E. Diagnosis and treatment of vitamin B12 deficiency — an update. Haematologica 91, 1506–1512 (2006).
Bailey, R. L. et al. Modeling a methylmalonic acid-derived change point for serum vitamin B-12 for adults in NHANES. Am. J. Clin. Nutr. 98, 460–467 (2013).
Morris, M. S. et al. Elevated serum methylmalonic acid concentrations are common among elderly Americans. J. Nutr. 132, 2799–2803 (2002).
Loikas, S. et al. Renal impairment compromises the use of total homocysteine and methylmalonic acid but not total vitamin B12 and holotranscobalamin in screening for vitamin B12 deficiency in the aged. Clin. Chem. Lab. Med. 45, 197–201 (2007).
Carmel, R. Anemia and aging: an overview of clinical, diagnostic and biological issues. Blood Rev. 15, 9–18 (2001).
Green, R. & Dwyre, D. M. Evaluation of macrocytic anemias. Semin. Hematol. 52, 279–286 (2015).
Lachner, C., Steinle, N. I. & Regenold, W. T. The neuropsychiatry of vitamin B12 deficiency in elderly patients. J. Neuropsychiatry Clin. Neurosci. 24, 5–15 (2012).
Reynolds, E. Vitamin B12, folic acid, and the nervous system. Lancet Neurol. 5, 949–960 (2006).
Biemans, E. et al. Cobalamin status and its relation with depression, cognition and neuropathy in patients with type 2 diabetes mellitus using metformin. Acta Diabetol. 52, 383–393 (2015).
Clarke, R. et al. Low vitamin B-12 status and risk of cognitive decline in older adults. Am. J. Clin. Nutr. 86, 1384–1391 (2007).
Doets, E. L. et al. Vitamin B12 intake and status and cognitive function in elderly people. Epidemiol. Rev. 35, 2–21 (2013).
O’Leary, F., Allman-Farinelli, M. & Samman, S. Vitamin B12 status, cognitive decline and dementia: a systematic review of prospective cohort studies. Br. J. Nutr. 108, 1948–1961 (2012).
Vogiatzoglou, A. et al. Cognitive function in an elderly population: interaction between vitamin B12 status, depression, and apolipoprotein E ε4: the Hordaland Homocysteine Study. Psychosom. Med. 75, 20–29 (2013).
Aisen, P. S. et al. High-dose B vitamin supplementation and cognitive decline in Alzheimer disease: a randomized controlled trial. JAMA 300, 1774–1783 (2008).
McMahon, J. A. et al. A controlled trial of homocysteine lowering and cognitive performance. N. Engl. J. Med. 354, 2764–2772 (2006).
Eussen, S. J. et al. Effect of oral vitamin B-12 with or without folic acid on cognitive function in older people with mild vitamin B-12 deficiency: a randomized, placebo-controlled trial. Am. J. Clin. Nutr. 84, 361–370 (2006).
Durga, J. et al. Effect of 3-year folic acid supplementation on cognitive function in older adults in the FACIT trial: a randomised, double blind, controlled trial. Lancet 369, 208–216 (2007).
Sato, Y. et al. Effect of folate and mecobalamin on hip fractures in patients with stroke: a randomized controlled trial. JAMA 293, 1082–1088 (2005).
Dangour, A. D. et al. A randomised controlled trial investigating the effect of vitamin B12 supplementation on neurological function in healthy older people: the Older People and Enhanced Neurological function (OPEN) study protocol [ISRCTN54195799]. Nutr. J. 10, 22 (2011).
Hvas, A. M., Morkbak, A. L. & Nexo, E. Plasma holotranscobalamin compared with plasma cobalamins for assessment of vitamin B12 absorption; optimisation of a non-radioactive vitamin B12 absorption test (CobaSorb). Clin. Chim. Acta 376, 150–154 (2007).
Bor, M. V. et al. Nonradioactive vitamin B12 absorption test evaluated in controls and in patients with inherited malabsorption of vitamin B12. Clin. Chem. 51, 2151–2155 (2005).
Hvas, A. M. et al. The vitamin B12 absorption test, CobaSorb, identifies patients not requiring vitamin B12 injection therapy. Scand. J. Clin. Lab. Invest. 71, 432–438 (2011).
Carkeet, C. et al. Human vitamin B12 absorption measurement by accelerator mass spectrometry using specifically labeled 14C-cobalamin. Proc. Natl Acad. Sci. USA 103, 5694–5699 (2006).
Stabler, S. P. Vitamin B12 deficiency. N. Engl. J. Med. 368, 2041–2042 (2013).
Toh, B. H. Diagnosis and classification of autoimmune gastritis. Autoimmun. Rev. 13, 459–462 (2014).
Lahner, E. et al. Reassessment of intrinsic factor and parietal cell autoantibodies in atrophic gastritis with respect to cobalamin deficiency. Am. J. Gastroenterol. 104, 2071–2079 (2009).
de Benoist, B. Conclusions of a WHO Technical Consultation on folate and vitamin B12 deficiencies. Food Nutr. Bull. 29 (Suppl. 2), S238–S244 (2008).
World Health Organization. The implications for training of embracing: a life course approach to health (WHO, 2000).
Duggan, C. et al. Vitamin B-12 supplementation during pregnancy and early lactation increases maternal, breast milk, and infant measures of vitamin B-12 status. J. Nutr. 144, 758–764 (2014).
Siddiqua, T. J. et al. Vitamin B12 supplementation during pregnancy and postpartum improves B12 status of both mothers and infants but vaccine response in mothers only: a randomized clinical trial in Bangladesh. Eur. J. Nutr. 55, 281–293 (2016).
Watanabe, F. Vitamin B12 sources and bioavailability. Exp. Biol. Med. (Maywood) 232, 1266–1274 (2007).
Naik, S. et al. Daily milk intake improves vitamin B-12 status in young vegetarian Indians: an intervention trial. Nutr. J. 12, 136 (2013).
Potdar, R. D. et al. Improving women's diet quality preconceptionally and during gestation: effects on birth weight and prevalence of low birth weight — a randomized controlled efficacy trial in India (Mumbai Maternal Nutrition Project). Am. J. Clin. Nutr. 100, 1257–1268 (2014).
Kehoe, S. H. et al. Effects of a food-based intervention on markers of micronutrient status among Indian women of low socio-economic status. Br. J. Nutr. 113, 813–821 (2015).
Winkels, R. M. et al. Bread cofortified with folic acid and vitamin B-12 improves the folate and vitamin B-12 status of healthy older people: a randomized controlled trial. Am. J. Clin. Nutr. 88, 348–355 (2008).
Dhonukshe-Rutten, R. A. et al. Effect of supplementation with cobalamin carried either by a milk product or a capsule in mildly cobalamin-deficient elderly Dutch persons. Am. J. Clin. Nutr. 82, 568–574 (2005).
Tapola, N. S. et al. Mineral water fortified with folic acid, vitamins B6, B12, D and calcium improves folate status and decreases plasma homocysteine concentration in men and women. Eur. J. Clin. Nutr. 58, 376–385 (2004).
Mohammad, M. A. et al. Plasma cobalamin and folate and their metabolic markers methylmalonic acid and total homocysteine among Egyptian children before and after nutritional supplementation with the probiotic bacteria Lactobacillus acidophilus in yoghurt matrix. Int. J. Food Sci. Nutr. 57, 470–480 (2006).
Miller, J. W. et al. Metabolic evidence of vitamin B-12 deficiency, including high homocysteine and methylmalonic acid and low holotranscobalamin, is more pronounced in older adults with elevated plasma folate. Am. J. Clin. Nutr. 90, 1586–1592 (2009).
Selhub, J., Morris, M. S. & Jacques, P. F. In vitamin B12 deficiency, higher serum folate is associated with increased total homocysteine and methylmalonic acid concentrations. Proc. Natl Acad. Sci. USA 104, 19995–20000 (2007).
Carmel, R. How I treat cobalamin (vitamin B12) deficiency. Blood 112, 2214–2221 (2008).
Obeid, R., Fedosov, S. N. & Nexo, E. Cobalamin coenzyme forms are not likely to be superior to cyano- and hydroxyl-cobalamin in prevention or treatment of cobalamin deficiency. Mol. Nutr. Food Res. 59, 1364–1372 (2015).
Berlin, H., Berlin, R. & Brante, G. Oral treatment of pernicious anemia with high doses of vitamin B12 without intrinsic factor. Acta Med. Scand. 184, 247–258 (1968).
Kuzminski, A. M. et al. Effective treatment of cobalamin deficiency with oral cobalamin. Blood 92, 1191–1198 (1998).
Castelli, M. C. et al. Comparing the efficacy and tolerability of a new daily oral vitamin B12 formulation and intermittent intramuscular vitamin B12 in normalizing low cobalamin levels: a randomized, open-label, parallel-group study. Clin. Ther. 33, 358–371.e2 (2011).
Kim, H. I. et al. Oral vitamin B12 replacement: an effective treatment for vitamin B12 deficiency after total gastrectomy in gastric cancer patients. Ann. Surg. Oncol. 18, 3711–3717 (2011).
Rajan, S. et al. Response of elevated methylmalonic acid to three dose levels of oral cobalamin in older adults. J. Am. Geriatr. Soc. 50, 1789–1795 (2002).
Eussen, S. J. et al. Oral cyanocobalamin supplementation in older people with vitamin B12 deficiency: a dose-finding trial. Arch. Intern. Med. 165, 1167–1172 (2005).
Bor, M. V. et al. Daily intake of 4 to 7 μg dietary vitamin B-12 is associated with steady concentrations of vitamin B-12-related biomarkers in a healthy young population. Am. J. Clin. Nutr. 91, 571–577 (2010).
Green, R. et al. Absorption of biliary cobalamin in baboons following total gastrectomy. J. Lab. Clin. Med. 100, 771–777 (1982).
Green, R. in Advances in Thomas Addison's Diseases (eds Bhatt, R., James, V. H. T., Besser, G. M., Bottazzo, G. F. & Keen, H.) 377–390 (Society for Endocrinology & The Thomas Addison Society, 1994).
Kumar, N. Neurologic aspects of cobalamin (B12) deficiency. Handb. Clin. Neurol. 120, 915–926 (2014). A complete description of the protean neurological manifestations of B12 deficiency.
Pittock, S. J., Payne, T. A. & Harper, C. M. Reversible myelopathy in a 34-year-old man with vitamin B12 deficiency. Mayo Clin. Proc. 77, 291–294 (2002).
Hirota, W. K. et al. ASGE guideline: the role of endoscopy in the surveillance of premalignant conditions of the upper GI tract. Gastrointest. Endosc. 63, 570–580 (2006).
Finkelstein, J. L., Layden, A. J. & Stover, P. J. Vitamin B-12 and perinatal health. Adv. Nutr. 6, 552–563 (2015).
Vogiatzoglou, A. et al. Vitamin B12 status and rate of brain volume loss in community-dwelling elderly. Neurology 71, 826–832 (2008).
Zhang, Y. et al. Decreased brain levels of vitamin B12 in aging, autism and schizophrenia. PLoS ONE 11, e0146797 (2016).
Stone, N. et al. Bioinformatic and genetic association analysis of microRNA target sites in one-carbon metabolism genes. PLoS ONE 6, e21851 (2011).
Joslin, A. C. et al. Concept mapping one-carbon metabolism to model future ontologies for nutrient-gene-phenotype interactions. Genes Nutr. 9, 419 (2014).
Grarup, N. et al. Genetic architecture of vitamin B12 and folate levels uncovered applying deeply sequenced large datasets. PLoS Genet. 9, e1003530 (2013). An informative and detailed description of the genetic blueprint of the architecture of the genome as it applies to B12 status as well as the closely related vitamin B9 (folate).
Deegan, K. L. et al. Breast milk vitamin B-12 concentrations in Guatemalan women are correlated with maternal but not infant vitamin B-12 status at 12 months postpartum. J. Nutr. 142, 112–116 (2012).
Ford, C. et al. Vitamin B12 levels in human milk during the first nine months of lactation. Int. J. Vitam. Nutr. Res. 66, 329–331 (1996).
Thomas, M. R. et al. The effects of vitamin C, vitamin B6, vitamin B12, folic acid, riboflavin, and thiamin on the breast milk and maternal status of well-nourished women at 6 months postpartum. Am. J. Clin. Nutr. 33, 2151–2156 (1980).
Greibe, E. & Nexo, E. Forms and amounts of vitamin B12 in infant formula: a pilot study. PLoS ONE 11, e0165458 (2016).
Strand, T. A. et al. Vitamin B-12, folic acid, and growth in 6- to 30-month-old children: a randomized controlled trial. Pediatrics 135, e918–e926 (2015).
Hussein, L. et al. Serum vitamin B12 concentrations among mothers and newborns and follow-up study to assess implication on the growth velocity and the urinary methylmalonic acid excretion. Int. J. Vitam. Nutr. Res. 79, 297–307 (2009).
Jenssen, H. B. et al. Biochemical signs of impaired cobalamin function do not affect hematological parameters in young infants: results from a double-blind randomized controlled trial. Pediatr. Res. 74, 327–332 (2013).
Bhate, V. K. et al. Vitamin B12 and folate during pregnancy and offspring motor, mental and social development at 2 years of age. J. Dev. Orig. Health Dis. 3, 123–130 (2012).
Bhate, V. et al. Vitamin B12 status of pregnant Indian women and cognitive function in their 9-year-old children. Food Nutr. Bull. 29, 249–254 (2008).
Strand, T. A. et al. Cobalamin and folate status predicts mental development scores in North Indian children 12–18 mo of age. Am. J. Clin. Nutr. 97, 310–317 (2013).
Leishear, K. et al. Relationship between vitamin B12 and sensory and motor peripheral nerve function in older adults. J. Am. Geriatr. Soc. 60, 1057–1063 (2012).
Lildballe, D. L. et al. Association of cognitive impairment with combinations of vitamin B12-related parameters. Clin. Chem. 57, 1436–1443 (2011).
Smith, A. D. & Refsum, H. Vitamin B-12 and cognition in the elderly. Am. J. Clin. Nutr. 89, 707S–711S (2009).
McLean, R. R. et al. Plasma B vitamins, homocysteine and their relation with bone loss and hip fracture in elderly men and women. J. Clin. Endocrinol. Metab. 93, 2206–2212 (2008).
Park, S. et al. Age-related hearing loss, methylmalonic acid, and vitamin B12 status in older adults. J. Nutr. Elder. 25, 105–120 (2006).
Gopinath, B. et al. Homocysteine, folate, vitamin B-12, and 10-y incidence of age-related macular degeneration. Am. J. Clin. Nutr. 98, 129–135 (2013).
Herbert, V. & Zalusky, R. Interrelations of vitamin B12 and folic acid metabolism: folic acid clearance studies. J. Clin. Invest. 41, 1263–1276 (1962).
Allen, L. H. Folate and vitamin B12 status in the Americas. Nutr. Rev. 62, S29–S33 (2004).
Brito, A. et al. Folate and vitamin B12 status in Latin America and the Caribbean: an update. Food Nutr. Bull. 36 (Suppl. 2), S109–S118 (2015).
Campbell, A. K. et al. Plasma vitamin B-12 concentrations in an elderly latino population are predicted by serum gastrin concentrations and crystalline vitamin B-12 intake. J. Nutr. 133, 2770–2776 (2003).
MacFarlane, A. J., Greene-Finestone, L. S. & Shi, Y. Vitamin B-12 and homocysteine status in a folate-replete population: results from the Canadian Health Measures Survey. Am. J. Clin. Nutr. 94, 1079–1087 (2011).
Quay, T. A. et al. High prevalence of suboptimal vitamin B12 status in young adult women of South Asian and European ethnicity. Appl. Physiol. Nutr. Metab. 40, 1279–1286 (2015).
Clarke, R. et al. Detection of vitamin B12 deficiency in older people by measuring vitamin B12 or the active fraction of vitamin B12, holotranscobalamin. Clin. Chem. 53, 963–970 (2007).
Karabulut, A. et al. Premarital screening of 466 Mediterranean women for serum ferritin, vitamin B12, and folate concentrations. Turk. J. Med. Sci. 45, 358–363 (2015).
Benson, J. et al. Low vitamin B12 levels among newly-arrived refugees from Bhutan, Iran and Afghanistan: a multicentre Australian study. PLoS ONE 8, e57998 (2013).
Sivaprasad, M. et al. Status of vitamin B12 and folate among the urban adult population in South India. Ann. Nutr. Metab. 68, 94–102 (2016).
El-Khateeb, M. et al. Vitamin B12 deficiency in Jordan: a population-based study. Ann. Nutr. Metab. 64, 101–105 (2014).
Thuesen, B. H. et al. Lifestyle and genetic determinants of folate and vitamin B12 levels in a general adult population. Br. J. Nutr. 103, 1195–1204 (2010).
el Kholty, S. et al. Portal and biliary phases of enterohepatic circulation of corrinoids in humans. Gastroenterology 101, 1399–1408 (1991).
Lai, S. C. et al. The transcobalamin receptor knockout mouse: a model for vitamin B12 deficiency in the central nervous system. FASEB J. 27, 2468–2475 (2013).
Tateyama, M. et al. CD4 T lymphocytes are primed to express Fas ligand by CD4 cross-linking and to contribute to CD8 T-cell apoptosis via Fas/FasL death signaling pathway. Blood 96, 195–202 (2000).
Refsum, H. et al. Holotranscobalamin and total transcobalamin in human plasma: determination, determinants, and reference values in healthy adults. Clin. Chem. 52, 129–137 (2006).