Yuzu.

Yuzu juice is a concentrated ascorbate source, and ascorbate is the single most effective dietary enhancer of non-heme iron absorption. It reduces ferric iron to the ferrous form and keeps it soluble at intestinal pH. The effect requires the two to be present in the same meal, not hours apart. This is textbook nutrition chemistry rather than anything specific to yuzu.

Hesperidin and narirutin are rutinosides, and human intestinal enzymes cannot cleave the rhamnose linkage. Colonic bacteria with alpha-rhamnosidase activity perform that hydrolysis, releasing hesperetin and naringenin for absorption. That makes the resident microbial community a rate-limiting step for citrus flavanone availability. Whether supplementing a specific strain improves the conversion in practice has not been established.

Yuzu juice and peel both carry ascorbate, so a yuzu preparation added on top of a vitamin C supplement raises total intake from two sources. Ascorbate above the absorptive transporter's capacity is simply excreted, so stacking has a ceiling. Count what the yuzu contributes rather than assuming it is negligible or that it replaces a supplement. The amount depends heavily on processing, since ascorbate degrades with heat and oxygen.

Hesperetin and quercetin are both handled by intestinal and hepatic UDP-glucuronosyltransferases and sulfotransferases. Given together, they compete for that conjugating capacity, which can raise the unconjugated fraction of one or both. The direction is predictable from enzymology, the magnitude in people is not characterised. Read it as mechanistic.

Curcumin and citrus flavanones are both cleared largely by glucuronidation, and both have shown inhibition of UGT activity in laboratory systems. Co-administration therefore has a plausible mutual effect on clearance. Nobody has quantified this pairing in humans. Anyone on a medication cleared by glucuronidation should raise it with their prescriber rather than assume the interaction is trivial.

Citrus flavanones inhibit OATP-family uptake transporters in the intestine and catechins interact with the same efflux and conjugation systems. The consequence is that neither compound behaves the same alone as it does in combination. This matters most for anyone taking a medication that depends on OATP uptake. It is a pharmacokinetic caution, not a benefit claim.

Calcium salts need to stay soluble to be absorbed, and citrate is a well characterised solubilising ligand for calcium. Citrus juice contributes citrate along with its other acids. The practical effect on absorption from a mixed meal is modest and depends on which calcium salt is involved. Calcium citrate already carries its own ligand, so the addition matters less there.