So, why isn't such a widespread issue causing mass epidemics of vitamin A deficiency? Simple: in the Western world, carotenoids provide less than 30% of people's vitamin A intake, whereas animal foods provide over 70% (8). An omnivorous BCMO1 mutant can generally skate by on vitamin A from animal sources, blissfully unaware of the carotenoid battle waging within.
But for those who eschew animal products, the effects of a dysfunctional BCMO1 gene will be obvious — and eventually detrimental. When poor converters go vegan, they can eat carrots until they're orange in the face (literally!) without actually obtaining enough vitamin A for optimal health. Carotenoid levels simply rise (hypercarotenemia), while vitamin A status nosedives (hypovitaminosis A), leading to deficiency amidst seemingly adequate intake (3).