Many autistic children have a deficiency of Vitamin B12, which is vital for the proper functioning of the brain and nervous system. This article examines the functions and benefits of vitamin B12. Group B vitamins can act individually or in combination with the cellular enzymes to form vitamin B co-enzymes. These vitamin B co-enzymes are crucial to the metabolic pathways that generate the energy from carbohydrates, fat and protein, needed by every cell in the body.
Because they are co-dependent in their metabolic activities, a deficiency of one B vitamin can affect optimal functioning of organ systems throughout the body. Therefore, B vitamins are best taken in combination as vitamin B complex. However certain B vitamins like B12 and folic acid are more crucial, and these may be needed at higher doses. Many autistic children have a deficiency of Vitamin B12, which is vital for the proper functioning of the brain and nervous system. This article examines discusses how to diagnose and correct any deficiencies.
Causes of Vitamin B12 deficiency
Vitamin B12 is the largest vitamin known. Being a very large molecule, it is not easily absorbed. Our body developed a sophisticated system to absorb B12 requiring the production of intrinsic factor in the stomach that attaches to the B12 and allows the complex to be absorbed in the end of the small intestine. This intrinsic factor is produced through a very sophisticated and complex biochemical pathway requiring about 30 enzyme-mediated steps for its synthesis.
Vitamin B12 deficiency can occur in the following situations:
- Reduced intrinsic factor production due to damaged stomach mucosal lining as seen in stomach ulceration, Helicobacter infection and stomach surgery (stomach stapling bariatric surgery)
- Low gastric hydrochloric production as seen in those on antacids or proton pump inhibitors and in old people.
- Impaired small intestine absorption (malabsorption) as seen in people with imbalanced intestinal flora (dysbiosis) commonly found in autism, and small intestine removal commonly done in Crohn’s disease.
- Poor dietary intake as seen among vegetarian and vegans who do not supplement their diet with B12 or use B12 fortified food. This is especially important in infants born to strict vegetarian mothers.
- Exposed to nitrous oxide (laughing gas anesthesia) as seen in dental offices and hospital operating room, and elderly undergoing surgery. Nitrous oxide inhibits the action of B12 when the tissue stores are low.
How to diagnose Vitamin B12 deficiency?
The clinical presentation of vitamin B12 deficiency varies considerably and rarely includes all the classic features, such as megaloblastic anemia, peripheral neuropathy, and subacute combined degeneration of the spinal cord.
More typically, vitamin B12 deficiency presents as nonspecific symptoms of fatigue, lassitude, malaise, vertigo, and cognitive impairment. Moreover, the clinical severity of vitamin B12 deficiency is unrelated to vitamin B12 concentrations, reflecting the limitations of standard vitamin B12 assays.
Accurate identification of vitamin B12 deficiency is important because inappropriate treatment with folic acid will correct the hematologic signs of vitamin B12 deficiency but leave the neurologic symptoms unaltered.
Tests for B12 deficiency
Serum total homocysteine (tHcy) concentrations.
Normal <15umol/L
Rationale: Vitamin B12 acts as a co-factor for methionine synthase, the enzyme that remethylates homocysteine to methionine by using 5-methyltetrahydrofolate as a methyl donor. Deficiency of either folate or vitamin B12 results in increased serum tHcy concentrations. Therefore, a raised tHcy implicates the presence of folate or vitamin B12 deficiency.
Serum methylmalonic acid (MMA) concentrations.
Normal < 0.35umol/L
Rationale: Vitamin B12 acts as a cofactor for methylmalonyl-CoA mutase, which converts methylmalonyl-CoA to succinyl-CoA; hence, deficiency of vitamin B12 results in elevated serum concentrations of methylmalonic acid (MMA). Therefore, elevated concentrations of MMA indicate vitamin B12 deficiency.
Cerebral spinal fluid methylcobalamin concentrations.
Rationale: Only the methylcobalamin form of vitamin B12 is beneficial for the brain and central nervous system. It is found only in the cerebral spinal fluid (CSF) where it acts as the crucial co-enzyme for the synthesis of the methyl group for the DNA, RNA and proteins production in neuron and myelin sheath regeneration, growth and maintenance. However, there is no other simpler way to estimate the CSF methylcobalamin concentrations. An autistic child may have impaired methylcobalamin metabolism without the increased MMA in serum or urine.
Dr. Ang Poon Liat
MBBS, M.Med (Paediatric), MRCP (UK Paediatric), FAMS, MD
Senior Consultant Pediatrician
