Mechanically (in the games and in VR), vitamins like Calcium and Iron do not boost stats in any way that regular old hard work and training wouldn't! The stats involved, called Effort Values (or EVs), are a (formerly) "hidden" mechanical element, raised "naturally" by battling other Pokemon. Vitamins give you a way to boost them early and control what stats get boosted to some extent, but do not raise the maximum number of EVs a Pokemon can invest (252, in case you wanted to know.) Because of this, Trainers in VR can absolutely buy vitamins and use them on their Pokemon, but there's no need to track or report this information! It's just a bit of flavour for you, the player, to include or exclude as you wish.