¹Sitaram Bhartia Institute of Science and Research, B-16, Qutab Institutional Area, New Delhi, India
²Amity Institute of Food Technology, Amity University, Amity Road, Sector-125 Noida-201301, Uttar Pradesh, India

^*Corresponding author: Rawat S, Department of Research and Clinical Epidemiology, Sitaram Bhartia Institute of Science and Research, B-16, Qutab Institutional Area, New Delhi, India Email: swapnil.rawat@gmail.com

Copyright: © 2021 Rawat S, et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Vitamin B12 plays a vital role in normal brain functioning. Its deficiency is associated with developmental delays, irritability, and failure to thrive in children. Several studies have evaluated the possibility of B-12 deficiency leading to ASD/ADHD with inconsistent results. This review summates the available literature on B12 deficiency/supplementation and ASD/ADHD in children. The literature search was conducted in Medline and Extended Medline using the following search words (Vitamin B12 or Cobalamin or Methylcobalamin or Cyanocobalamin) and (Autism, Autistic spectrum disorder or attention deficit hyperactivity disorder or ASD or ADHD). Total of sixteen studies were retrieved of which four were clinical trials. Most of the observational studies report an association between B-12 deficiency and Autism. Studies on ADHD are fewer, and the association is weaker. Intervention studies were only available for ASD. Three of these reported improvement in biochemical and/or clinical behavior ratings for ASD children while one study did not show any improvement in either. There is observational data documenting the relationship between B-12 dfefficiency and ASD. Studies on ADHD are fewer and less conclusive. Intervention studies using B-12 in ASD children document biochemical improvement. There is paucity of trial literature on the clinical impact of B-12 supplementation in ASD especially in terms of behavior ratings. Further work should be urgently considered to address these lacunae.

Vitamin B12; Autism; Attention Deficit Hyperactivity Disorder

Vitamin B12 is a water-soluble vitamin required for the development and initial myelination of central nervous system and normal functioning of the brain. Vitamin B12 (B12) is an essential cofactor for two enzymes involved in one‐carbon metabolism: methylmalonyl CoA mutase (reduced function of this enzyme results in increased serum methylmalonyl acid (MMA) levels) and methionine synthetase (this enzyme catalyzes the remethylmation of homocysteine to methionine). A serum B12 level below the normal expected range may indicate B12 deficiency [1]. Levels of B12 along with methylmalonic acid (MMA) and homocysteine are usually measured to detect the B12 deficiency [2]. Well-documented adult consequences of B12 deficiency include pernicious anemia, megaloblastic anemia, peripheral neuropathy neuropsychiatric syndromes and subacute combined degeneration of spinal cord [2,3,4]. Vitamin B12 (cobalamin) deficiency has been previously thought to be rare in children; however, recent studies suggest that the condition is more common than previously recognized [5]. Vitamin B12 deficiency in children is known to present with nonspecific manifestations, such as developmental delay, irritability, weakness, and failure to thrive. B-12 deficiency is becoming increasingly critical in India with the high prevalence of deficiency and the rising prevalence of vegetarianism. Recently many researchers have attempted to evaluate the potential role of the deficiency in childhood neurological syndromes like Autistic spectrum and Attention Deficit Hyperactivity Disorder. The current review seeks to summate the current evidence in this regard.

Vitamin B12 is found primarily in foods of animal origin. When consumed, vitamin B12 is released from food proteins in the stomach and binds to R-binder proteins, made in the saliva and stomach. After exposure to pancreatic proteases, vitamin B12 is released from the R proteins in the small intestine and forms a complex with intrinsic factor, produced in gastric parietal cells. The intrinsic factor-vitamin B12 complex is taken up in the terminal ileum, after recognition by specific ileal receptors. The complex dissociates in the enterocyte, and the free vitamin enters the portal circulation bound to transcobalamin II, which transports vitamin B12 to tissues. Vitamin B12 is secreted in bile and reabsorbed in the ileum, conserving B12 in individuals with normal absorption [5]. Although the adult recommended dietary allowance for vitamin B12 is 2.4 μg/d, an adult stores about 2 to 3 mg (primarily in the liver) [6].

Table 1 lists the current Recommended Dietary Allowances (RDA) by National Institute of Nutrition, 2020 for vitamin B12 across all age groups [7].

The Institute of Medicine (IOM) did not establish a Upper Limit for vitamin B12 because of its low potential for toxicity. In Dietary Reference Intakes, the IOM states that “no adverse effects have been associated with excess vitamin B12 intake from food and supplements in healthy individuals” [6].

In patients with vitaminB12 deficiency, two oral regimens have been shown to achieve neurologic and hematologic response in the short term. Effective dosages were 2,000 μg daily or 1,000 μg daily for 10 days, then weekly and monthly [8].

Vitamin B12 is contraindicated in known hypersensitivity to the vitamin or to cobalt. Patients who have early Leber’s disease develop severe and swift optic atrophy on treatment with vitamin B12. Hypokalemia and sudden death are reported when severe megaloblastic anemia is treated aggressively. Indiscriminate administration of vitamin B12 may mask the true diagnosis of pernicious anemia. Multiple vitamin deficiency is expected in any dietary deficiency.

Most antibiotics, methotrexate and pyrimethamine invalidate folic acid and vitamin B12 diagnostic microbiological blood assays. Chloramphenicol may antagonize the hematopoietic response to vitamin B12. Hematopoietic response in such patients should be monitored.

Colchicine, aminoglycosides, certain anticonvulsants (e.g., Phenytoin, Phenobarbital, Primidone), para-aminosalicylic acid or excessive alcohol intake may impair the absorption of vitamin B12. Vitamin C may destroy vitamin B12. Patients should avoid ingesting large amounts of vitamin C within 1 hour of oral vitamin B12 administration.

May cause vitamin B12 insufficiency by reducing gastric acid cleavage of vitamin B12 from food sources. This may be important in patients with low stores of vitamin B12 or in patients taking H2- antagonists for extended periods of time (>2 years).

No adverse effects have been reported.

Vitamin B12 is distributed into the milk of nursing women in concentrations that approximate the maternal blood vitamin B12 concentration. No adverse effects have been reported.

Autism Spectrum Disorder (ASD) is a neurological and developmental disorder characterized by impaired social interaction, abnormal communication and repetitive or unusual behavior [10,11]. Prevalence of ASD is reported to be 1 in 160 children globally [12]. ASD begins from childhood and tends to persist into adolescents and adulthood. By the age of three, all typical symptoms such as impaired social reciprocity, poor communication skills and restricted for repetitive behavior, affecting three major domains are observed. Associated co-morbidities include epilepsy, bowel disorder, intellectual disability and type -I diabetes. ADHD on the other hand includes attention difficulty, hyperactivity and impulsive behavior. Children with ADHD have difficulty in concentrating on single task or sitting still for long period of time [13]. Its presence increases difficulties in academic performance and social interactions besides leading to low self-esteem. Up to 9.4% of United States children are diagnosed with ADHD [14].

Vitamins and minerals are required for normal growth and development of children. Vitamin B-12 is known to be necessary for the synthesis of myelin in the body. The development and pattern of myelination follows a well-described neuroanatomical arc [15], progressing in a posterior-to-anterior and centre-outwards spatiotemporal pattern that corresponding to maturing cognitive functions [16]. That is, there is a strong overlap in the emergence of a specific cognitive function and the myelination of brain regions and networks sub serving that function.

Hence it was hypothesized by several researchers that childhood neurodevelopmental anomalies like ASD or ADHD could be related to a deficiency of Vitamin B-12. Hence we undertook a review of literature of the subject to define the scope of existing knowledge on the subject.

We conducted searches in Medline, Extended Medline (1950 to 22 July 2020) using the following search words (Vitamin B12 or Cobalamin or Methylcobalamin or Cyanocobalamin) and (Autism, Autistic spectrum disorder or attention deficit hyperactivity disorder or ASD or ADHD). We imposed no age or language restrictions. We also reviewed reference lists of identified articles and hand-searched reviews, bibliographies of books, and abstracts. We scanned the titles and abstracts of the trials identified in the computerized search to exclude studies that were obviously irrelevant. We scrutinized the full texts of the remaining studies and identified relevant observational and interventional studies. The studies identified by this exercise are presented in Table 2.

Several observational studies have documented that children with ASD or ADHD are deficient in B-12 as reflected in the biochemical B-12 parameters [17-27]. Table 2 summaries the observational data on the subject. As presented Pasca et al and Altun et al noted that children with autism have significant higher levels of total homocysteine and lower levels of B12 in plasma as compared to age matched controls [17,26]. A study of Omani children found that ASD have low dietary intake of B12 and thus have low serum B12 levels compared to neurotypical controls [20]. Another research on homocysteine levels in urine found to be significantly higher in autism children [18]. While most studies on ASD children document B-12 deficiency in children with ASD the results of Chen et al and Guo et al differed from this general trend. Chen J, in China studied 68 ASD children and documented that maternal serum levels of vitamin B12 and homocysteine were not significantly associated with risk of ASD.23 Guo et al, in China studied 371 children (274 ASD) aged 2-7 years using the Autism Behavior Checklist and their Social responsiveness scale. No significant difference was found regarding vit B12 between ASD group and control group (p = >0.106) [26].

Two studies report observational data on B-12 levels in children with ADHD. Both recorded lower B-12 levels in ADHD children than in controls but the levels in ADHD were higher than those of children with ASD. Bala et al analysed and compared B-12 levels in ASD (n=34) [22], ADHD (n=16) and controls (n=27) and noted that the ASD group had the lowest vitamin B12 levels, whereas the vitamin B12 levels of the ADHD group were significantly lower compared to the controls. Similarly, Yektas et al compared vitamin B12, folate and homocysteine concentrations in ASD (n=48), ADHD (n=35) and controls (n=35) [28]. ASD had the lowest vitamin B12 and the highest homocysteine levels while ADHD had intermediate levels. They also noted that Oppositionality and hyperactivity and/or impulsivity may be related to vitamin B12 and homocysteine levels in children with ADHD.

Pubmed search yielded only 4 Intervention studies using B-12 in children with ASD/ADHD (all were for ASD). Of these only two studies report the impact of supplementation on behavioral rating and biochemical B-12 status together. Hendren et al randomized 57 children with ASD to receive either 8 weeks of treatment with methyl B12 (75 mcg/kg) or saline placebo every 3 days in a subcutaneous injection [29]. The primary outcome measure was overall improvement in symptoms of ASD as measured by the Clinical Global Impressions- Improvement (CGI-I) score. Secondary outcome measures included changes in the Aberrant Behavior Checklist (ABC) and the Social Responsiveness Scale (SRS). Laboratory measures of methionine methylation and antioxidant glutathione metabolism were assessed at baseline and 8 weeks. The primary outcome measure - the clinician rated CGI-I score -was statistically significantly better (lower) in the methyl B12 group (2.4) than in the placebo group (3.1) (0.7 greater improvement in the methyl B12 group, 95% CI 1.2–0.2, p = 0.005). Clinical improvement among children treated with methyl B12 was positively correlated with increases in plasma methionine (p = 0.05), decreases in S-adenosyl-l homocysteine (SAH) ( p = 0.007) and improvements in the ratio of S-adenosylmethionine (SAM) to SAH ( p = 0.007), indicating an improvement in cellular methylation capacity. No improvements were observed in the parent-rated ABC or SRS.

However, Bertoglio et al in a cross over trial did not find any statistically significant differences in the overall [30]. However, Nine (9 of 30) subjects (30%) demonstrated clinically significant improvement on the Clinical Global Impression Scale and at least two additional behavioral measures. More notably, these responders exhibited significantly increased plasma concentrations of GSH and GSH=GSSG means for behavior or glutathione endpoints between active and placebo groups. This led the authors to conclude that methyl B12 may alleviate symptoms of autism in a subgroup of children, possibly by reducing oxidative stress. An increase in glutathione redox status (GSH=GSSG) may provide a biomarker for treatment response to methyl B12. Also, the cross-over design of the study may not be most appropriate to answer the study question given that cobalamin could be stored in the liver for a long time up to 2 to 3 years.

The other two studies primarily evaluated the impact of supplementation on biochemical parameters. James SJ, et al. in 2009, supplemented 40 autistic children with 75 μg/kg methylcobalamin (2 times/wk) and 400 μg folinic acid (2 times/d) for 3 months [31]. Plasma concentrations of transmethylation/ transsulfuration metabolites and glutathione redox status in autistic children were measured as compared to controls. There were significant increases in cysteine, cysteinylglycine, and glutathione concentrations (P < 0.001). The oxidized disulfide form of glutathione was decreased and the glutathione redox ratio increased after treatment (P < 0.008). Kaluzna et al recruited 51 children (30 ASD and 21 controls) [2,3]. Autistic children were supplemented daily with Group A1: vitamins B6, B12, and folic acid and Group A2: vit B6 and B12 in the dose of 200 mg, 1.2 μg, and 400 μg, respectively. All children followed a sugar-free diet. Pre vs post-treatment (A1 and A2) in autistic children: Homocysteine levels:

2.41 ± 1.10 vs 1.13 ± 0.44 and 1.33 ± 0.39 mmol/mol creatinine for A1 and A2 groups, respectively. The authors concluded that the intake of vitamins B6 and B12, together with folic acid, was more effective in lowering the levels of urinary homocysteine than the intake of vitamins B6 and B12 alone.

In conclusion, there is strong theoretical basis for the role of Vitamin B-12 in DNA methylation and nerve myelination and hence it is a potential suspect for neurodevelopmental disorders of childhood like ASD and ADHD. Deficiency of B-12 is common worldwide and especially in India. The deficiency is reported to be particularly severe in vegetarian populations. There is ample observational data (with a few exceptions) from developed countries documenting the relationship between B-12 deficiency and ASD. Studies on ADHD are fewer and hence less conclusive. Intervention studies using B-12 in ASD children have consistently demonstrated biochemical improvement. There is paucity of trial literature on the clinical impact of B-12 supplementation in cases with ASD in terms of behavior ratings. The few existing studies were only from developed countries and support a potential role for B-12 supplementation in children with ASD although the evidence is not strong. The studies were conducted with small sample sizes, showed weak differences and were weak in design. While it is possible that B-12 might be the effect of restricted dietary preferences in neurologically compromised children. It is also possible that some of the neurological effects of deficiency at a developmentally sensitive stage may not be reversible. None of the studies were conducted in micro-nutritionally highrisk settings or in developing countries. Also, none of studies have evaluated the preventive or longer-term impact of supplementation. Further work should hence be urgently considered to address these lacunae.

The authors did not receives any financial compensation for creating this manuscript

The authors declare no conflict of interest

Author contributions: SR and JN conceived the idea. SR conducted review of literature. SR drafted the manuscript. All authors have read, reviewed, edited and approved the final manuscript.

Consent: All the authors consent for publication

Ethical Approval: No ethical approval was taken as per institutional policy.