Glossary
Bioavailability.
Direct answer
Bioavailability describes the share of an ingested nutrient or substance that actually reaches the bloodstream in a form the body can use. Decisive factors include the chemical form, the food matrix, the site of absorption along the digestive tract and interactions with other components. Two products with identical declared content may therefore behave differently.
A common error is to treat the declared content of a product as the amount actually taken up. The label states what the product contains, not what the body extracts from it. Whether a mineral is present as a chelate or as an inorganic salt changes its solubility, and therefore the fraction that crosses the gut wall at all.
In the horse, digestive architecture shifts the calculation further: much of the fibre is broken down only in the large intestine, downstream of the main site of mineral and vitamin uptake. What caecal fermentation delivers is therefore available in a different way than in humans, whose fermentation compartment is proportionally much smaller.
The evidence letter
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