Ferrous sulfate anhydrous.

Ascorbic acid reduces ferric iron to ferrous and holds it soluble through the duodenum, where uptake happens. This pairing is the standard way iron salts are formulated.

Vitamin C in the same dose counters phytate and polyphenol binding of iron in the gut lumen. More of the anhydrous salt's iron then reaches the transporter.

A calcium dose taken with iron lowers non-heme iron uptake at the intestinal step. Spacing the two several hours apart keeps both intakes usable.

Zinc and iron compete for DMT1 when both arrive as large single doses. Split dosing avoids the competition without lowering either amount.

Copper-containing ferroxidases load absorbed iron onto transferrin. Adequate copper is what lets iron move out of storage and into circulation.

Folate supports the cell division of marrow precursors while iron fills their hemoglobin. The pathway moves only as fast as the scarcer of the two.

B12 works with folate on the DNA synthesis step that dividing red cell precursors depend on. Iron supplies the heme those cells then load.

Vitamin A status affects the release of stored iron from ferritin into circulation. Adequate vitamin A lets a given iron intake show up more fully in blood.

Flavins made from riboflavin support the reduction step that frees ferritin iron for transport. Riboflavin status therefore changes iron utilisation.

Tea catechins bind non-heme iron into complexes that cannot cross the enterocyte. Co-dosing lowers the iron the salt actually delivers.

Phytase degrades the phytate that otherwise binds most non-heme iron in a plant meal. Iron uptake rises because the inhibitor is gone, not because the dose changed.

Quercetin chelates ferrous iron in the lumen and lowers uptake when taken in the same window. The two are better separated in time.

DMT1 in the duodenal brush border carries ferrous iron and also carries manganese, and the two compete for the same carrier when they arrive together. A large iron dose lowers manganese uptake in the same window, and a high manganese load does the same in the other direction. Spacing the doses is the usual answer.

Galloyl groups on tannins bind iron in the gut lumen and form insoluble complexes that the enterocyte cannot take up. Tea, coffee and tannin-rich extracts taken with an iron salt reduce the absorbed fraction substantially. Separating the two by a couple of hours restores most of the uptake.

Curcumin's beta-diketone group binds iron, and in animal work high curcumin intake lowers iron status markers. Taken in the same sitting as a ferrous salt it can reduce the fraction available for absorption. Human dose-response for this interaction has not been characterised.

Alpha lipoic acid and its reduced form bind transition metals including iron, which is the basis of its metal-handling reputation. Co-ingestion with an iron salt can lower the absorbed fraction. Formulators separate the two by a few hours.

Ferrous sulfate needs gastric acid to stay in solution long enough to reach the absorptive duodenum. Anything that raises gastric pH sharply, including a bicarbonate load, drives conversion to poorly soluble ferric hydroxide species. The practical rule is not to take an alkalising agent alongside the iron dose.

Activated charcoal adsorbs a wide range of luminal solutes non-selectively, and mineral salts taken in the same window are adsorbed along with everything else. Any iron dose given near charcoal should be assumed to be reduced. Standard practice is to separate them by several hours.

Bentonite carries a negatively charged aluminosilicate lattice that exchanges and holds divalent cations, iron included. Taken with a ferrous salt it binds a share of the dose in the lumen. Dosing them apart is the formulation answer.

Viscous soluble fibre slows gastric emptying and traps mineral cations within the gel, lowering the fraction presented to the duodenal surface. The effect is modest compared with tannins or phytate but it is real for a same-sitting dose. Separation by a couple of hours is the usual practice.

Fermentation of inulin produces short-chain fatty acids that acidify the colonic lumen and keep iron in a more soluble state, and some human work suggests improved iron absorption with prebiotic co-administration. Findings across studies are not consistent. The claim here is about absorption, not about iron status outcomes.

Galactooligosaccharides ferment proximally and lower luminal pH, which favours the soluble ferrous state. Trials pairing them with ferrous salts have reported improved absorption in some groups. Results vary with baseline iron status.

Lactoferrin binds ferric iron tightly and delivers it by a receptor route distinct from DMT1 uptake of free ferrous iron. That is why it is used as an alternative iron carrier rather than a booster of a ferrous salt. Combining the two changes which route the dose takes rather than simply adding to it.

Unabsorbed ferrous iron in the gut lumen participates in Fenton chemistry, generating hydroxyl radicals that propagate lipid peroxidation. Tocopherols terminate that chain in the lipid phase. The pairing addresses local oxidative chemistry and is not a claim about iron status.

Lactic acid bacteria lower luminal pH and some strains produce compounds that alter iron solubility, and unabsorbed iron in turn shifts colonic bacterial composition. The interaction runs both ways. Human data on co-supplementation are limited.

Lysine has been added to iron regimens in small studies of people whose iron markers did not respond to iron alone, with reported improvement in ferritin. The mechanism is not settled and the trials are small. This is an association in a marker, not a demonstrated cause.