Final answer:
Ascorbic acid enhances iron absorption by reducing ferric iron to a more soluble ferrous form, aiding in its uptake in the gastrointestinal tract. Other dietary and physiological factors can also influence iron absorption. Reduced iron is used in food fortification primarily for its neutral taste and cost-effectiveness.
Step-by-step explanation:
When ascorbic acid is taken with iron sulfate, it enhances iron absorption. This is mainly because ascorbic acid (cysteine is another reducing agent mentioned) helps convert ferric iron (Fe³⁺) into the ferrous state (Fe²⁺), which is more soluble and, consequently, more readily absorbed in the gastrointestinal tract where the acidic pH favors this absorption. Factors such as diet, disease, and removal of parts of the digestive system can also significantly affect iron absorption. For example, a diet high in phosphate, phytic acid, and oxalic acid can decrease iron absorption, while conditions like pernicious anemia or the administration of alcohol can increase it.
The question of why we ingest metallic iron, such as that added to food as reduced iron, is explained by a few reasons including that it does not affect the taste of food, its impact on food preparation is minimal, and it's less expensive than iron salts.