Table 1. Main Enhancers and Inhibitors of Iron Absorption.

type of study	component/dose	experimental model	main results	reference
in vivo	ascorbic acid/25 to 1000 mg	63 male subjects	As vitamin C dose was increased from 25 to 1000 mg, absorption of iron showed an increase from 0.8% to 7.1% in male subjects who were fed with a liquid formula meal containing 4.1 mg of iron.	(56)
in vitro	ascorbic acid/-	caco-2 cell	Ascorbic acid enhanced the absorption only when it was added along with the digests to Caco-2 cells during the iron uptake study.	(50)
in vitro	ascorbic acid/-	caco-2 cells	While phytic acid, sodium oxalate, and sodium silicate decrease iron absorption, ascorbic acid has the ability to counteract their inhibitory effects.	(51)
in vivo	animal tissue/25 g	8 healthy infants 43–49 weeks of age	Inclusion of meat to the vegetable puree significantly increased the nonheme iron absorption.	(64)
in vivo	animal tissue/25, 50, or 75 g	45 healthy women with a mean age of 24 ± 3 years	Dose–response increase was observed when pork meat was added to a high-phytate, low-ascorbic-acid meal.	(65)
			While 25 g of meat did not influence the nonheme iron absorption, inclusion of 50 and 75 g of meat increased the absorption significantly (44% and 57%, respectively).
in vivo	animal tissue/-	randomized crossover trial in 21 young women with low iron stores	Addition of fish to high-phytate bean meal enhanced the iron bioavailability.	(66)
in vitro	animal tissue/-	caco-2 cell	Caco-2 cells’ response to nonheme iron from infant rice was significantly increased by bovine coproducts (kidney, lung, and heart).	(67)
			For the kidney, lung, and heart, relative uptake of iron was found to be 207.13%, 171.21%, and 265.28%, respectively.
in vivo	phytate/-	58 men and 60 women, aged 19–58 years	Iron absorption was significantly increased by the removal of phytates in bran.	(74)
			The addition of potassium and magnesium phytates in amounts present in bran showed an inhibition of iron absorption.
in vivo	phytate/seven dose levels from 2 to 250 mg	34 men and 90 women, aged 19–47 years	Inhibitory effect of phytate was dose dependent.	(76)
			Ascorbic acid may reduce the inhibitory impact of phytate.
in vivo	phytate/718 to 1190 mg/d in the high-phyate group and 623 to 385 mg/d in the low phytate group	32 nonanemic females, 18–35 years of age, with suboptimal iron stores	Inhibitory effects of phytate on nonheme iron absorption were lessened by eating a high-phytate diet on a regular basis in young women with low iron status.	(79)
in vivo	phytate/-	720 pregnant women	Bioavailability of iron and calcium in the diets of pregnant women was inhibited by phytate intake.	(78)
in vivo	phytate/77 ± 11 mg	102 females aged between 20 and 30 years	12 weeks of high-phytate wholegrain bread consumption had no effect on iron status in women at reproductive age.	(80)
in vivo	phytate/817 ± 21 mg	14 women aged 19–42 years who were not habitually consuming iron-containing nutritional supplements	A significant effect of phytate content on iron absorption was not found when porridge was fortified with iron in the form of either sodium iron EDTA or ferrous sulfate.	(81)
in vivo	polyphenols/from 52 to 396 mg	23 males and 54 females aged 19–40 years	Black tea was more inhibitory than cocoa and more inhibitory than herbal teas camomile, vervain, lime flower, and pennyroyal but equivalent to peppermint tea at the same total polyphenol content.	(82)
in vivo	polyphenols/20, 50, and 200 mg	97 apparently nonpregnant, nonlactating women aged between 18 and 45 years and weighing below 60 kg	Red bean polyphenols inhibited iron bioavailability dose-dependently. While 20 mg of bean polyphenols had no effect on iron absorption, 50 mg and 200 mg lowered iron bioavailability by 18% and 45%, respectively.	(83)
in vitro	polyphenols/-	caco-2 cell	Polyphenolic compounds inhibited the heme iron absorption in a dose-dependent manner.	(121)
			In small amounts of polyphenols (≤4.6 mg/L) ascorbic acid counteracted the inhibitory effect; however, in higher levels (46 mg/L), it could not modulate the inhibition.
in vivo	polyphenols/-	17 mother–child pairs	Polyphenol-rich tea reduced iron absorption from wheat bread fortified with ferrous sulfate or ferrous fumarate by 56–72%.	(89)
in vivo	polyphenols/492 mg	50 women aged 21–30 years	In both IDA and nonanemic women, tea consumption decreased iron absorption from NaFeEDTA by more than 85%.	(90)
in vitro	polyphenols/-	caco-2 cell	Catechin, 3,4-dihydroxybenzoic acid, kaempferol, and kaempferol 3-glucoside promoted iron uptake, while myricetin, myricetin 3-glucoside, quercetin, and quercetin 3-glucoside showed an inhibitory effect.	(84)
in vivo	calcium/100 and 200 mg	788 children aged 6–11 years	As the ascorbic acid and calcium did not exist, iron absorption from the casein/whey-based drink was 20% lower in iron-repleted children than the ones with IDA.	(97)
			Calcium addition decreased the mean iron absorption by 18–27%.
in vivo	calcium/500 mg	13 premenopausal women with pre-existing marginal Fe status aged 28–35 years	Iron absorption from a single meal was reduced from 10.2% to 4.8%.	(95)
			The extent of the calcium impact differed significantly across subjects having similar iron stores.
in vitro	proteins/30 g	simulated gastrointestinal digestion	Iron absorption decreased by the substitution of casein or whey protein for egg white. Mean absorption values fell from 6.67 to 3.65% and 2.53 to 0.98%, respectively.	(122)
in vivo	proteins/30 g	15 men and 19 women ranging in age from 18 to 45 years	Iron absorption of completely dephytinized glycinin was found to be 124% compared to egg white; however, relative absorption of completely dephytinized conglycinin was only 44%. Conglycinin fraction of soybean proteins was reported to be an inhibitor of iron absorption.	(105)
in vivo	prebiotic/4% of the diet	40 female albino rats (ten-week-old)	Yogurt containing long-chain inulin was more effective for iron absorption than yogurt containing short-chain inulin.	(111)
			Fe2(SO4)3 and long-chain inulin fortified yogurt increased the iron bioavailability. In addition, liver function and the antioxidant capacity were improved.
in vivo	prebiotic/-	24 healthy women aged 35–45 years	No significant differences were observed in heme and nonheme iron bioavailability in the control group.	(109)
			Bioavailability of heme iron from the prebiotic group increased significantly by 56% after prebiotic intake.
			No significant differences were observed in nonheme iron bioavailability.
in vivo	prebiotic/∼20 g	36 nonpregnant, nonlactating women with low iron status, aged between 18 and 40 years and with a body weight <65 kg	Inulin enhanced the iron absorption by 14% which was statistically insignificant.	(110)