Do BCMO1 variants reduce beta-carotene conversion and raise vitamin A deficiency risk?

Mechanistic insights

• The beta-carotene 15,15'-monooxygenase 1 (BCMO1) enzyme cleaves dietary provitamin A carotenoids into retinal, which is subsequently reduced to active retinol.
• Key coding polymorphisms, specifically R267S (rs12934922) and A379V (rs7501331), directly impair this pathway. In vitro assays of the double-mutant (267S + 379V) show a 57% reduction in catalytic activity. In human trials, carriers of A379V alone experience a 32% reduction, while double-variant carriers exhibit an approximate 69% reduction in converting oral beta-carotene to retinyl esters.
• Upstream regulatory variants (rs6420424, rs11645428, and rs6564851) further decrease in vivo cleavage activity by 48% to 59%. This compromised kinetics leads to a "low responder" phenotype characterized by elevated circulating beta-carotene levels (hypercarotenaemia) and a low yield of systemic retinoids.

Clinical implications

• While omnivores easily bypass compromised BCMO1 activity by consuming preformed vitamin A from animal products, individuals adhering to strict vegan or vegetarian diets rely entirely on plant-derived carotenoids.
• Under dietary conditions that isolate the carotenoid pathway, these genetic conversion deficits directly increase the risk of subclinical or clinical vitamin A insufficiency. For instance, studies in children and adolescents carrying the low-activity A379V TT variant demonstrate a significant inverse association with overall vitamin A status.

Bottom line

• Genetic variants in the BCMO1 gene (such as R267S and A379V) reduce the conversion of plant-derived beta-carotene to active vitamin A by 32% to 69%. This reduction significantly elevates the risk of vitamin A insufficiency in individuals who rely heavily or exclusively on plant carotenoids.