This review in 2018 offers an update to the understanding of genetic polymorphisms relating to B12 metabolism and function. This review found 16 studies that showed 59 B12 related gene polymorphisms associated with more ethnically diverse populations. These results demonstrate the necessity for active supplementation as the impact of genetic polymorphisms was previously downplayed.
References:
Surendran S, Adaikalakoteswari A, Saravanan P, Shatwaan IA, Lovegrove JA, Vimaleswaran KS. An update on vitamin B12-related gene polymorphisms and B12 status. Genes Nutr. 2018;13:2. Published 2018 Feb 6. doi:10.1186/s12263-018-0591-9 https://pubmed.ncbi.nlm.nih.gov/29445423/