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Effect of phytic acid, tannic acid and pectin on fasting iron bioavailability both in the presence and absence of calcium

https://doi.org/10.1016/j.jtemb.2014.11.005Get rights and content

Abstract

Objective

To determine the effect of phytic acid, tannic acid and pectin on fasting non-heme iron bioavailability in both the presence and absence of calcium.

Research methods

Twenty-eight apparently healthy adult females participated in two iron absorption studies using radioactive iron isotopes (59Fe and 55Fe). One group received 5 mg of iron (as FeSO4) alone (control), together with 10 mg of phytic acid, 100 mg of tannic acid and 250 mg of pectin (study A), on different days. The second group received the same iron doses and compounds as the other group, plus 800 mg of calcium (CaCl2) (study B). The compounds were administered after an overnight fast, and no food or beverages were consumed for the following 3 h. Iron status and circulating radioactivity were measured in venous blood samples.

Results

The geometric means of iron bioavailability (range ± 1SD) for iron alone, iron with phytic acid, iron with tannic acid, and iron with citrus pectin were 25.0% (11.9–52.0); 18.9% (9.9–35.8); 16.8% (8.7–32.3); and 21.1% (10.2–43.9), respectively (repeated-measures ANOVA, p < 0.02 (Dunnett's post hoc: control vs tannic acid p < 0.05). When 800 mg of calcium was added (study B), iron bioavailability was 16.7% (10.1–27.5); 13.2% (7.1–24.6); 14.8% (8.8–25.1); and 12.6% (5.5–28.8), respectively (repeated-measures ANOVA, NS).

Conclusions

Tannic acid decreases the fasting bioavailability of non-heme iron, however this effect did not exist in the presence of calcium. No effect was observed by phytic acid or citrus pectin on fasting non-heme iron bioavailability in both the presence and absence of calcium.

Introduction

Iron deficiency anemia remains the most prevalent nutritional deficiency in developed and developing countries [1]. In addition to this, it has been estimated that a large proportion of adolescents and adults do not reach the current dietary recommendations for calcium [2]. The interaction between calcium supplementation and compounds present in foods and beverages that contain iron may be an important factor in the deficiency of both of these nutrients. Both micronutrient deficiencies may produce negative consequences on health. Adequate dietary calcium throughout the life cycle is important for ensuring bone mineralization, for rickets prevention in children, and for long-term bone loss prevention [3]. Iron deficiency adversely affects the cognitive development of children [4], increases maternal and infant mortality, and reduces physical work capacity in adulthood [5], [6].

Diets characterized by low iron bioavailability [7], are one of the main causes of iron deficiency anemia. The following compounds have been recognized as inhibitors of non-heme iron absorption: phytate, some proteins (soy, milk and egg yolk), calcium [8], zinc [9], manganese [10], and tannic acid [11]. It has been postulated that pectin may also inhibit the absorption of non-heme iron [12], [13]. Regarding the effect of calcium, it has been suggested that this mineral interacts with components in food matrices, inhibiting the absorption of non-heme iron. One study showed an inhibitory effect of phytic acid on iron absorption in the presence of calcium [14]. Although it has been thought that calcium may have a direct inhibitory effect on iron absorption, a recent article [15] showed that doses ≤800 mg of calcium (Ca molar ratio: Fe  225:1), do not diminish the bioavailability of 5 mg of non-heme iron. Evidence on the interaction between calcium and phytic acid and their effect on the absorption of non-heme iron is scarce. The effect of the interaction between calcium and tannic acid, and the interaction between calcium and pectin, on the bioavailability of non-heme iron, is unknown. Thus, the present study investigates the effect of one dose of phytic acid, tannic acid and pectin on the fasting bioavailability of 5 mg of non-heme iron, in both the presence and absence of calcium.

Section snippets

Subjects

Twenty-eight apparently healthy multiparous adult women voluntarily participated in two iron absorption studies. All women were using contraception methods. Exclusion criteria were pregnancy (confirmed by a negative human gonadotropin chorionic urine test), lactation and the use of micronutrient supplements within 6 months prior to the start of the study.

Ethics

A written informed consent was obtained from 6677809‴. The Ethics Committee of the Institute of Nutrition and Food Technology at the

Baseline characteristics

All women who voluntarily participated in these two studies were adults aged 30–47 years. None of the volunteers presented iron deficiency anemia. In study A, two women had iron deficiency without anemia and one iron depleted stores. According to the calculation of body iron, a volunteer in study A and one in study B presented iron deficiency in tissues. In study B, three women had iron deficiency without anemia (data not shown). Table 2 summarizes the general characteristics such as age, BMI

Discussion

The present study investigates the effect of one dose of phytic acid, tannic acid and pectin on fasting bioavailability of 5 mg of non-heme iron in both the presence and absence of calcium. In the presence of 100 mg of tannic acid, we observed a significant decrease in the bioavailability of 5 mg of iron (FeSO4). It has been estimated that 100 mg of tannic acid is the approximate amount found in one cup of tea (250 mL), prepared with 5 g of tea leaves/L of water [24]. In fasting conditions, without

Conclusions

One-hundred mg of tannic acid significantly decreases the fasting bioavailability of 5 mg of non-heme iron (FeSO4), while 10 mg of phytic acid and 250 mg of high methoxyl citrus pectin had no effect. The same compounds in the presence of 800 mg of calcium (CaCl2), did not affect the bioavailability of 5 mg FeSO4.

Conflict of interest

The authors declare no conflicts of interest.

Acknowledgments

We would like to thank Sotiris Chaniotakis for his diligent work editing this manuscript. The study was supported by grants FONDECYT 1030090 by the Chilean National Research Council.

References (43)

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