Essential Vitamins & Minerals /

Vitamin B12

01 In Brief

Vitamin B12 is an essential water-soluble vitamin found in animal protein such as meat, fish and dairy as well as other fortified foods. Women who are pregnant or lactating need to have sufficient levels of Vitamin B12 to prevent their baby from suffering serious side effects such as anaemia and irreversible neurological problems. Exclusively breast fed babies can rapidly deplete these stores if their mother is Vitamin B12 deficient. The level of Vitamin B12 in breast milk reflects the dietary intake and absorption of Vitamin B12 of the mother rather than the reserves you have. Women at risk include strict vegetarians/vegans and those with gastrointestinal disorders, which can often be undetected.

02 What Do I Need To Know?

• Vitamin B12 is a water soluble vitamin that is naturally present only in animal proteins. It is present in several forms and contains the mineral cobalt, hence Vitamin B12 compounds are known as cobalamins. As humans do not synthesise Vitamin B12 they are dependent on dietary intake.
• Food sources of Vitamin B12 include meat, fish, poultry, eggs, milk and milk products. It is not present in plant products but may be in some fortified foods such as plant milks, some soy products and breakfast cereals.
• Vitamin B12 is required for red blood cell formation and for neurological and metabolic functions of the body. Vitamin B12 present in food is attached to food proteins. Acid present in the stomach releases Vitamin B12 from food proteins to form free Vitamin B12. Vitamin B12 present in fortified foods does not need this step and is already free B12. Free B12 then combines with Intrinsic Factor (IF) to form Intrinsic Factor /B12 complex which is then transported through the small intestine to be absorbed in the end part of the small intestine known as the terminal ileum.
• IF is a protein that is secreted by the parietal cells present in the stomach lining. It combines with Vitamin B12 to allow transport through the small intestine and then absorption in the terminal ileum. Without IF, transport and absorption cannot occur.
• Vitamin B12 deficiency results from:  
  • Inadequate dietary intake;
  • Disorders of the stomach, such as malabsorption disorders, inflammatory bowel disease, after surgery, lack of Intrinsic Factor due to an auto immune disorder (where antibodies are formed that attack the parietal cells of the stomach, known as pernicious anaemia), drugs e.g. antacids and metformin (used for diabetes), decreased stomach acidity, tapeworm infestation, and changes in the bacterial flora in the bowel with a resultant overgrowth of bacteria;
  • Disorders of the terminal ileum, such as surgery, inflammatory bowel disease.

VITAMIN B12 IN PREGNANCY

• Although Vitamin B12 is stored in significant quantities in the body, it is actively transported across the placenta to the fetus during pregnancy. This results in a progressive decline in the mothers' Vitamin B12 levels and stores. At birth a newborn's Vitamin B12 can be up to four times higher than the mother's. Maternal B12 deficiency is therefore common during pregnancy and smoking reduces levels even further. Although mild deficiency does not tend to pose a risk to the mother or newborn, severe deficiency has been associated with an increased likelihood of neural tube defects and miscarriage.
•  The recommended daily intake of Vitamin B12 for non-pregnant women is 2.4 micrograms (mcg). For pregnant women this only marginally increases to 2.6mcg and to 2.8mcg for breast feeding women. 

BREAST FEEDING AND VITAMIN B12

• Infants born to Vitamin B12-deficient mothers have very limited stores of Vitamin B12. Vitamin B12 is excreted into breast milk and the levels in colostrum are relatively high in the first 48 hrs. Subsequent levels of Vitamin B12 drop and correlate to dietary intake rather than maternal stores. Exclusively breast-fed babies can develop symptoms of Vitamin B12 deficiency by two to 12 months of age. The symptoms are often insidious and slow in onset, and these subtle signs may escape diagnosis until several months later. 
• Signs of Vitamin B12 deficiency in infants include:
  
  • Anaemia;
  • Lethargy;
  • Failure to thrive;
  • Floppiness;
  • Developmental delay.
• In some cases the developmental delay is associated with severe abnormalities of the white matter of the brain and these changes may be irreversible.

INVESTIGATION FOR VITAMIN B12 DEFICIENCY: TOTAL AND ACTIVE B12 LEVELS

• Vitamin B12 in blood is bound to two proteins Transcobalamin (TC) and Haptocorrin (HC). These complexes are known as TC-B12 or active B12 and HC-B12 or non active B12.
  • Active B12 is B12 that is in a chemical form that is available for cells to use and consists of 20 per cent of the total Vitamin B12 measured in the blood. 
  • Non active B12 contributes of 80 per cent of the total.
  • The combination of the active and non active levels is measured when a standard (total) Vitamin B12 test is ordered. 
• Until recently Vitamin B12 was  assessed by measuring the standard or total Vitamin B12 level. Recent evidence suggests that this sometimes does not accurately reflect what is happening at the cellular level i.e. where it is needed, especially when the total level is between 150-250 pmol/l i.e. the indeterminate range.
• In this indeterminate range there is now a move towards measuring active Vitamin B12, which is a more accurate reflection of Vitamin B12 levels that are available for the cells to utilise. The level of active B12 corresponds with total B12 only at the extremes of measurement i.e. if the total level is very low, < 150, or high, >250. At levels of150-250pmol/l the total standard level may be in the normal range but the active B12 may be in the deficient range. Hence, early onset of Vitamin B12 deficiency may be missed if total Vitamin B12 is relied upon.
• Infants and children with developmental delay should have their Vitamin B12 levels measured as part of routine investigations. A urine metabolic screen may sometimes detect abnormalities of certain acids (methylmalonic acid and homocystine) which would alert the doctor to a possible Vitamin B12 deficiency. In this circumstance an active B12 level would be a more useful assessment. 
• All mothers of Vitamin B12-deficient infants should have their Vitamin B12 level measured and should also receive treatment where appropriate.

TREATMENT OF VITAMIN B12 DEFICIENCY

• Treatment of Vitamin B12 deficiency in infants is considered a medical emergency. However, babies respond rapidly to Vitamin B12 supplements, which are usually given by injection.

GENETIC CONGENITAL VITAMIN B12 DEFICIENCY 

• There are rare forms of Vitamin B12 deficiency that occur in infants due to a genetic disorder. This is where the infant is either unable to produce Intrinsic Factor, produces an abnormal Intrinsic Factor or has an abnormality of the receptors in the terminal ileum required for absorption of Vitamin B12 (Imerslund-Grasbeck Syndrome).
• Those with defects of Intrinsic Factor present in the first few months of life with developmental delay, whereas those with defects of the receptors present after the baby's first year of life.
  
• Diagnosis is complex and investigations are required to determine whether it is the infant's inability to absorb Vitamin B12 that is the cause of the deficiency, or whether it is a result of a maternal deficiency.

03 What Others Say

• Royal Women's Hospital Fact sheet 

Vegetarian eating and pregnancy

• Royal Australian and New Zealand College of Obstetricians and Gynaecologists - statement on vitamins and minerals in pregnancy 

Vitamin and Mineral Supplementation in Pregnancy

• Veganhealth.com wesite fact sheet 

Veganhealth Infants and Toddlers

04 I Want To Know More

• National Health and Medical Research Council  

nhmrc-nutrient-values.pdf">Nutrient Reference Values for Australia and New Zealand

• National Institute of Health US:  Office of Dietary Supplements - provides a good summary about Vitamin B12

Dietary Supplement fact sheet Vitamin B12

• Summary of Active B12 measurement compared to total

Abbott company summary of active B12 measurement

• Recent Case reports of 15 Turkish infants with Vitamin B12 deficiency 

Neurological findings of nutritional Vitamin B12 deficiency in children

05 Clinicians Tools and Resources

• Case Report Vit B12 deficiency: Pediatrics 2003; 112; 684-686

Involuntary Movements and MRI findings in Infantile B12 deficiency

• VeganHealth.Org - an excellent page with a list of case reports of infants and toddlers with reported B12 deficiency

Case Reports Vit B12 deficiency

• Dieticians Association of Australia

 Nutrient Reference Values and what they mean 

• Reference Book on metabolic diseases

Inherited Metabolic Diseases: A Clinical Approach - Google Books Result

Last updated: 12/07/2011 by Dr Elizabeth Hallam*/Claire Galea

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