GLOSSARY

Intrinsic Factor is a gastric protein supporting specialized cobalamin uptake in the terminal small intestine.

Food-bound B12 must first be released, then normally uses gastric intrinsic factor and absorption in the terminal small intestine. A small fraction can also enter by an independent pathway. Package amount is therefore not the absorbed amount, and gastric or ileal problems can impair status despite adequate food. These mechanisms help explain why dietary and medical correction strategies can differ.

Vitamins do not share one uptake route; water or fat solubility provides a useful starting point rather than explaining every exception. Food release, carriers, bile or binding proteins can contribute. Greater intake does not always increase absorption proportionally, and some excess is excreted. Athletes benefit from adequate food and identifying deficiency causes rather than competing for the largest package number or assuming every formulation behaves alike.

The small intestine is central to uptake of many nutrients and digestion by pancreatic and brush-border enzymes. The duodenum receives bile and pancreatic secretions; later regions also absorb extensively. Terminal regions specialize in processes such as bile-salt recovery and intrinsic-factor-dependent uptake. Regional distinctions do not mean every nutrient belongs exclusively to one tiny site or that all absorption finishes immediately after the stomach.