Dear Editor,

I read with great interest the article ‘Adequate vitamin B₁₂ and folate status of Norwegian vegans and vegetarians’ by Henjum et al. (2022)^{(Reference Henjum, Groufh-Jacobsen and Allen1)}. The authors conducted a cross-sectional study with 205 participants to evaluate the vitamin B₁₂ and folate status of Norwegian vegans and vegetarians using multiple approaches for it assessment. While acknowledging these results, I would also like to point some methodological issues and mainly provide a perspective about vitamin B₁₂ role during pregnancy and for the first years of life.

First, it is reported in the methodology that the participants were between 18 and 60 years old, but in the discussion they say that in their sample only three participants were over 60 years old. Second, one of the inclusion criteria was no consumption of poultry, meat and/or meat products the previous 6 months or more; however, as the body storage of vitamin B₁₂ is quite long, a greater restriction would probably result in different results for the study. Third, the study considers serum vitamin B₁₂ adequate above 221 pmol/l, but perhaps an analysis with a more rigorous cut-off point would bring interesting results given its importance for health. As a fourth question, the authors mention Fig. 1 in the results, but none is presented in the study. And finally, interestingly, in the population studied, there was no vitamin B₁₂ deficiency, although 14 % had low levels of vitamin B₁₂. In addition, vegan participants supplemented more vitamin B₁₂ than vegetarians, and older participants had higher serum concentrations of vitamin B₁₂ despite the majority of the population being women, young and of childbearing age. As the article only mentions the importance of vitamin B₁₂ in pregnancy and lactation, I would like to make some remarks about it.

The development of the central nervous system and the brain begins during the third week of pregnancy and continues through early childhood. Also myelination and synaptogenesis are processes that begin in the pregnancy in third trimester and continue to influence neuronal development in the offspring during the first years of life^{(Reference Georgieff2)}. In this, the vitamin B₁₂ plays an important role with potential effects on cognitive development that refers to the mental processes involved in memory, attention, learning and executive functions^{(Reference Venkatramanan, Armata and Strupp3)}. The child of a mother with a vitamin B₁₂ deficiency can be born with the deficiency or can become deficient during the period of exclusive breastfeeding as the concentrations of vitamin B₁₂ in human milk are strongly related to the state maternal during pregnancy and postpartum^{(Reference Williams, Stewart and Shahab-Ferdows4)}. Notably, the neurological manifestations of vitamin B₁₂ deficiency may precede or occur in the absence of hematological consequences; that is, deficiencies were often not diagnosed until permanent neurological damage had occurred^{(Reference Ralapanawa, Jayawickreme and Ekanayake5)}. For this reason, serum vitamin B₁₂ values considerably above the lower limit of the reference value are indicated.

Most of the initial data on childhood vitamin B₁₂ deficiency comes from case studies of infants exclusively breastfed by mothers on vegan or vegetarian diet. A baby born to a vegetarian or vegan mother is at high risk of being born with low vitamin B₁₂ stores and developing severe clinical signs of deficiency as failure in brain development with imaging showing atrophy and delays in myelination^{(Reference Georgieff2,Reference Allès, Baudry and Méjean6)} . Importantly, vegetarian women who have had repeated pregnancies put their babies at greater risk because their vitamin B₁₂ stores were likely depleted in previous pregnancies^{(Reference Sebastiani, Barbero and Borrás-Novell7)}. In vegan diets, the risk of nutrient inadequacy is supposedly greater than in vegetarian diets, as food selection is even more limited and unfortified plant foods, such as seaweed, do not contain any significant amounts of active vitamin B₁₂ ^{(Reference Sebastiani, Barbero and Borrás-Novell7,Reference Clarys, Deliens and Huybrechts8)} . However, in the study by Henjum et al. (2022),^{(Reference Henjum, Groufh-Jacobsen and Allen1)} vegans supplemented more vitamin B₁₂ which may change this risk of deficiency while vitamin B₁₂ supplementation results in rapid improvements in laboratory measurements of individuals’ status, but cognitive function may not show the same improvement^{(Reference Kwok, Lee and Ma9)}.

I respectfully thank Henjum et al. (2022)^{(Reference Henjum, Groufh-Jacobsen and Allen1)} for providing us with a valuable research that from it further studies should be designed. Vitamin B₁₂ deficiency is emerging as a public health problem in many countries with infants and pregnant women being the most vulnerable groups. So the relationship of maternal vitamin B₁₂ with that of her offspring highlights the crucial role of pregnancy in preventing vitamin B₁₂ deficiency in the next generation and should probably be the focus of future research.