What does bioavailability mean?
Bioavailability is a scientific noun describing how much of a substance — most often a drug or a nutrient — actually enters the bloodstream and becomes available to the body after it is administered. In pharmacology, it is quantified precisely: the percentage of a dose that reaches systemic circulation in an unaltered form, with a drug given directly into a vein serving as the reference standard of 100%. A medication swallowed as a tablet may lose much of its potency to digestion or first-pass metabolism in the liver, resulting in low oral bioavailability. The same concept extends into nutrition, where factors such as food pairing, cooking methods, and chemical form influence whether compounds like iron, curcumin, or vitamins are effectively absorbed. Because it captures the gap between what we consume and what our bodies truly take up, bioavailability has become a familiar term even outside laboratories, appearing frequently in conversations about supplements and healthy eating.
nounThe degree and rate at which a drug, nutrient, or other substance is absorbed into the bloodstream and becomes available at the site of physiological activity.
- In pharmacology, the fraction of an administered dose of a drug that reaches systemic circulation unchanged, typically expressed as a percentage (absolute bioavailability is measured relative to intravenous administration).
- More broadly in nutrition and environmental science, the extent to which a nutrient or chemical substance is accessible for uptake and use by a living organism.
"Taking vitamin D with a fatty meal can significantly improve its bioavailability."
"Because the drug undergoes extensive first-pass metabolism in the liver, its oral bioavailability is only about twenty percent."
"Cooking tomatoes actually increases the bioavailability of lycopene compared with eating them raw."
Rarely used; the word normally functions as an uncountable mass noun. A plural appears only when comparing distinct measured values across substances, formulations, or species.
"The study compared the oral bioavailabilities of the two formulations in human subjects."
A supplement can be 100% pure and still be nearly useless — if its bioavailability is low, your body may absorb only a tiny fraction of what's on the label.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of bioavailability
Bioavailability is a twentieth-century coinage formed from the combining form 'bio-' (from Greek bios, meaning life) attached to 'availability', which derives from Latin via Old French: avail traces back through Anglo-Norman and Old French to the Latin phrase ad valere, 'to be of worth or use'. The compound emerged in mid-twentieth-century pharmaceutical science as researchers sought a precise measure of drug absorption. Its roots are shared by words such as biology, biography, and available.
Related word forms
How bioavailability is actually used
A technical term belonging primarily to pharmacology, medicine, nutrition science, and toxicology; rarely used in casual conversation except in discussions of supplements and health products, where it is sometimes invoked loosely as a marketing claim. It is an uncountable noun — one speaks of high or low bioavailability rather than 'a bioavailability'.
Easily confused with bioavailability
Absorption refers to the process of a substance entering the bloodstream itself, whereas bioavailability is the measured fraction or extent of that substance that actually reaches circulation in an active form.