Refers to the body's ability to absorb and use a particular nutrient. Much may depend on the form in which the nutrient is supplied. For instance magnesium oxide and calcium carbonate supplements, though commonly sold in pharmacies, dissolve poorly in stomach acid. If a substance cannot dissolve, it is not very bioavailable, as it cannot get into the bloodstream. Some dietary supplements are coated with shellac, which prevents them from disintegrating. This, and packing powdered products too tightly together when tableting them, causes 'bed pan bullets' - products which emerge unchanged in the stools.

Supplements of inorganic minerals in the form of sulphates, chlorides, oxides and carbonates (called inorganic because they do not normally occur naturally in the plant or animal kingdom) tend to be less bioavailable than organic mineral compounds like gluconates, citrates, lactates and picolinates, which do. These compounds can be ingested in food or can be formed in the human body by the process of chelation and are highly bioavailable.

For the bioavailability of nutrients in foods, see the individual nutrients.

Bioflavonoids (see Flavonoids)