bioavailability

noun

1. (countable, uncountable)The extent to which a substance is molecularly available to cells and tissues in a living organism, which depends on factors such as solubility, pH level, and presence of enzymes and cofactors; for example, even if one's ingestion of vitamin B₁₂ is average/typical, one might nonetheless have B₁₂ deficiency if one has poor metabolism of this particular vitamin.
2. (countable, uncountable)The extent to which a substance is molecularly available to cells and tissues in a living organism, which depends on factors such as solubility, pH level, and presence of enzymes and cofactors; for example, even if one's ingestion of vitamin B₁₂ is average/typical, one might nonetheless have B₁₂ deficiency if one has poor metabolism of this particular vitamin.

   “poor/low oral bioavailability”