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Mineral absorption varies by mineral type and is tightly regulated: calcium absorption (40–60%) is enhanced by vitamin D and inhibited by phytates and oxalates; iron absorption differs between heme (15–35%) and non-heme iron (2–20%), regulated by hepcidin and duodenal transporters; zinc absorption (~20–30%) is reduced by phytates and competing minerals. Intestinal absorption is adjusted via hormonal feedback (parathyroid hormone for calcium, hepcidin for iron) to maintain serum concentrations within narrow ranges. Bioavailability of specific mineral forms (citrate vs. oxide, ferrous vs. ferric) affects clinical outcomes.
Create absorption profiles for different mineral forms and food matrices; compare fractional absorption of calcium from dairy versus plant sources under varying vitamin D status.
The body doesn't absorb minerals passively at whatever rate food delivers them — it actively regulates absorption to maintain serum concentrations within tight ranges. You already know from mineral homeostasis that calcium, phosphorus, and magnesium operate through hormonal feedback loops. The gut is the first control point: absorption efficiency is adjusted up or down depending on the body's current status. When you're calcium-deficient, the intestinal lining upregulates calcium transport machinery; when replete, it downregulates. This is called adaptive regulation, and it explains why a person with low stores absorbs a much higher fraction of a given dose than someone who is already replete.
From your study of bioavailability, you know that absorption is never 100% — it depends on the chemical form of the mineral and the food matrix surrounding it. For calcium, this plays out dramatically: dairy provides a soluble, bioavailable form absorbed at roughly 30–40%, while spinach provides calcium but also delivers oxalate, which binds calcium in the gut lumen and blocks absorption (fractional absorption drops to ~5%). For iron, the split between heme iron (from meat, 15–35% absorbed) and non-heme iron (from plants, 2–20%) reflects a fundamental difference in the absorptive machinery — heme iron is taken up as an intact porphyrin ring via a dedicated transporter, bypassing many of the dietary interactions that limit non-heme iron uptake.
The hormonal regulation of iron is governed by hepcidin, a peptide secreted by the liver in response to high iron stores, inflammation, or infection. Hepcidin acts by degrading ferroportin — the only known cellular iron export protein — on the surface of intestinal enterocytes and macrophages. When hepcidin rises, iron is trapped inside cells rather than entering the bloodstream; when iron stores fall, hepcidin drops, ferroportin is expressed, and absorption rises. This mechanism doubles as host defense: pathogens need iron too, and high hepcidin during infection starves them. It also explains why iron deficiency and anemia of chronic inflammation require different treatments — the former has low hepcidin and responds to oral iron; the latter has high hepcidin from inflammation and does not.
Supplement form matters in clinical practice. Calcium carbonate requires gastric acid for dissolution and is poorly absorbed in patients on proton pump inhibitors or with atrophic gastritis. Calcium citrate is pre-ionized and absorbed independently of stomach acid — preferable for those patients. Similarly, ferrous (Fe²⁺) salts are absorbed directly by the duodenal transporter DMT1, while ferric (Fe³⁺) salts must first be reduced by a brush-border enzyme — a rate-limiting step. Vitamin C enhances non-heme iron absorption by keeping iron in the ferrous state. These molecular details explain why clinical nutrition recommendations specify not just the mineral but the form, dose timing, and co-ingested foods — higher intake is not the same as higher absorption.