Reducing Effect of Ingesting Tannic Acid on the Absorption of Iron, but Not of Zinc, Copper and Manganese by Rats

Abstract

Interest in the beneficial effects of polyphenols, including tannic acid (TA), is increasing, although, these compounds also have adverse effects; for example, on the absorption of iron (Fe), and possibly other trace minerals. We examined the effect of a graded dose of TA on the absorption of Fe and compared with that of zinc (Zn), copper (Cu) and manganese (Mn) in rats. We also investigated the effect of TA on cecal fermentation which plays a role in absorption. In Experiment 1, to set the optimum dose of Fe, male Sprague-Dawley rats (weighing 70-90 g) after acclimatization were fed with different levels of dietary Fe (5, 10, 20, 30 and 35 mg/kg). We observed that the hematocrit (Ht), serum Fe concentration and transferrin saturation (%) were each reduced in those rats fed less than 20 mg/kg Fe in a dose-dependent manner. In Experiment 2, the rats were fed with test diets containing the minimum required level of Fe, 30 mg/kg diet, with (5, 10, 15 and 20 g/kg diet) or without TA for a period of three weeks. Feeding a diet containing more than 10 g TA/kg diet, but not 5 g TA/kg diet, reduced the hemoglobin concentration (Hb), Ht and serum Fe concentration due to decreased Fe absorption. In contrast, the Zn, Cu and Mn absorption was not affected by TA feeding. It is also demonstrated that liver Fe, but not the Zn, Cu and Mn contents, were lower in the TA groups than in the TA-free control group. Feeding TA slightly decreased the pH value of the cecal contents with an increase in the major short-chain fatty acid pool. About 15% of the ingested TA were recovered in the feces of each TA-fed group. Our results demonstrate that more than 10 g TA/kg diet induced anemia by reducing the Fe absorption, although there was no effect on the absorption of other important trace minerals. Our findings suggest that the usual intake of polyphenols is relatively safe, but that a high intake by supplementation or by dietary habit of tannin affects only the Fe level.

Effects of dietary grape seed extract on growth performance, amino acid digestibility and plasma lipids and mineral content in broiler chicks

“…These results were consistent with the studies of Cook et al (1995) and Marouani et al (2007) that showed that red wine, tea and other beverages rich in polyphenolic compounds inhibited the absorption of non-heme iron. In addition, in line with our results, supplementation of tannic acid (gallotannin) in the diets of weanling pigs and rats induced the formation of stable polyphenol/iron complexes in the gut having a negative impact on plasma iron concentration (Afsana et al, 2004;Lee et al, 2010). Nevertheless, the precise mechanism by which bioactive dietary polyphenolic compounds inhibit iron metabolism has not been delineated.…”

The role of condensed tannins in ruminant animal production: advances, limitations and future directions

“…Afsana et al (2004) demonstrated no effect of tannin supplementation on Zn absorption in vivo. Reports of CT complexes with other cations are scarce and usually related to tea consumption.…”

“…Condensed tannin-Fe complexes can effectively inhibit Fe absorption (Lavin et al, 2010;Wren et al, 2013) at levels as low as 5 g tannic acid/kg (Afsana et al, 2004). In cell culture, a 1:1 ratio of tannic acid to Fe inhibited 92% of Fe absorption (Glahn and Wortley, 2002).…”

Scientific Opinion on the safety and efficacy of tannic acid when used as feed flavouring for all animal species

“…EFSA received directly from the applicant the technical dossier in support of this application. 6 According to Article 8 of that Regulation, EFSA, after verifying the particulars and documents submitted by the applicant, shall undertake an assessment in order to determine whether the feed additive complies with the conditions laid down in Article 5. The particulars and documents in support of the application were considered valid by EFSA as of 9 August 2011.…”