Case report

A girl was referred to a hospital in the Capital Region of Denmark at the age of 10 months for arrested development, passive behaviour and peripheral and truncal hypotonia. She could not sit, and she had reduced coordination, dyskinetic movements and generalised, tonic–clonic seizures. The patient was anaemic at 1.8 mmol/L with megaloblastic changes, raised total p‐homocysteine at 88 μmol/L (normal reference <15 μmol/L) and p‐methylmalonate at 17.7 μmol/L (<0.28 μmol/L) and low p‐methionine at 3 μmol/L (5–34 μmol/L). Her p‐vitamin B12 was <33 pmol/L (140–543 pmol/L). Cerebral imaging revealed mild central and cortical atrophy. The girl's dietary history disclosed that both parents were vegans and gave their child a vegan diet without B12 supplementation. The mother had a low B12 level and an intramuscular injection of B12 resulted in a quick biochemical response. Unfortunately, the family was lost to follow‐up. This case was reported 10 years ago by us 1. It has been estimated that one infant per year with a similar clinical history has been referred in the Capital Region of Denmark, which has 22 000 births per year, and one case was published by Larsen in 2014 2. Similarly affected infants have been reported in the international literature 2-4. In its 2019 recommendation, and earlier recommendations, the Danish National Health Authorities advised parents to avoid a vegan diet when feeding young children 5. However, 10 years after our case report, affected children are still referred and the rising popularity of a vegan diet is cause for concern. The Danish recommendation parallels the 2017 guidelines from the European Society for Paediatric Gastroenterology Hepatology and Nutrition, which state: “Vegan diets have generally been discouraged during complementary feeding. Although theoretically a vegan diet can meet nutrient requirements when mother and infant follow medical and dietary advice regarding supplementation, the risks of failing to follow advice are severe, including irreversible cognitive damage from vitamin B12 deficiency, and death. If a parent chooses to wean an infant onto a vegan diet this should be done under regular medical and expert dietetic supervision, and mothers should receive and follow nutritional advice”6. The Society's position is paralleled by German 7 and Swiss 8 guidelines, which extend their advice to avoiding a vegan diet in pregnant and lactating women.

Frequency of plant‐based diets In the US adult population, about 3.7% followed a vegan diet in 2015 and for the age‐group 8–18 years it was 2% 4. In Germany, 2.1% of boys and 6.1% of girls aged 14–17 years were on a vegetarian diet 4. In a Danish cohort of 80 743 pregnant women in 1996–2002, 1.2% were vegetarians and 21 women were vegans 2. About 10% did not receive any vitamin supplements during pregnancy, irrespective of their diet 2.

B12 deficiency and plant‐based diets Vitamin B12 deficiency is to be expected when consuming a plant‐based diet, because B12 is found exclusively in food of animal origin. Such a diet is a risk for other deficiencies, including iodine, calcium, iron, docosahexaenoic acid, vitamin D and protein, and this should be taken into account when planning the diet. However, B12 is the main concern and is the focus here. B12 deficiency has been associated with many adverse clinical effects. During pregnancy, these have included foetal loss, intrauterine growth retardation with low birth weight, preterm delivery and neural tube defects. Deficiencies during infancy cause haematological, neurological and developmental manifestations, with long‐term neurodevelopmental impairment in some children 3, 4. When a plant‐based diet is followed without supplementing the diet with B12, biochemical signs of B12 deficiency are a consistent finding with low plasma B12 levels and pathological levels of biomarkers of B12 deficiency, including raised homocysteine and methylmalonate and low holotranscobalamin II and methionine 4. Data regarding the B12 status of pregnant and lactating vegan and vegetarian women and their children are scarce. One study found B12 deficiencies in 25% of vegan women and their children and another reported B12 deficiencies in 56% of lactating vegan mothers 4. In India, 57% of exclusively breastfed infants born to vegan mothers and 44% of their mothers were B12 deficient 9. In Nepal, 58% of breastfed children were B12 deficient 10. In Germany, 39% of pregnant vegetarian women had B12 deficiencies, compared with 9% of those who did not eat much meat and 3% of non‐vegetarian women 11. Importantly, vegan pregnant and lactating women normalise their B12 status after B12 supplementation 4. The B12 status in neonates has been strongly associated with maternal B12 status 12 and levels in breast milk have correlated with levels in maternal blood and with blood methylmalonate concentrations in their breastfed child 4. In pregnancies with normal maternal B12 status, the foetus stores B12 in the liver, but when women following a plant‐based diet do not take B12 supplements, storing becomes difficult because of low maternal B12 status. Together with low B12 levels in breast milk, this may lead to biochemical and clinical signs of B12 deficiency in their child. Limited studies of cohorts of vegan and vegetarian mothers and their children have documented this connection in biochemical terms, but a connection with clinical disease is harder to prove. Larsen et al. studied head circumference, age at sitting and walking in the cohort referred above and found no difference between children born to 986 vegetarians and those born to non‐vegetarian mothers. The study only included 21 vegan mothers, and data concerning child development were only available for 12 vegan children 2. Their development was normal in all cases. Biochemical evidence and clinical signs of B12 deficiencies in children, especially those who are born to vegan mothers, are well documented in the literature 4. The data referred to above, concerning B12 status in pregnant and lactating vegan or vegetarian mothers and their children, are limited. However, the body of evidence suggests that there is good reason to be concerned that a low B12 status associated to a plant‐based diet poses a health hazard for young children, especially those born to vegan mothers and being fed a diet without B12 supplements.