Most of the replicator food is true to the chemical makeup of the food it is replicating. Vitamins included.

Like food? Mmm... no, not quite. [He frowns a little, unsure of what to compare the thirium to.] It's more like blood, in a way. It does not need to be replenished very often. Androids can run for a number of years without consuming more thirium. Unless damage results in a significant loss of thirium.

[Luckily, he didn't have to plug into anything to recharge.]