The aim of our study was to examine the influence of tea decoction given ad libitum for 15 days on body weight gains and on nonheme iron, copper, zinc and magnesium concentrations in the blood from a semisynthetic diet provided to healthy rats. We have also evaluated the reserves of these essential minerals in the liver, duodenum and spleen. Our findings indicate that the tea decoction significantly reduced the total body weight growth in the tea group as compared to the control group (p < 0.0001). The total body weight gains for the control and tea groups were 13.2 and 2.4%, respectively. On the other hand, our data show that the tea decoction significantly reduced nonheme iron concentration in the total blood by 31.8% (p < 0.001). Similarly, the reserve of iron stored in the liver and the duodenum declined more significantly by 57% (p < 1 · 10^-7) and 50.5% (p < 1 · 10^-6), respectively. In contrast to the inhibitory effect on iron concentration and its stored reserve, tea decoction significantly increased zinc, copper and magnesium concentrations in the total blood. Zinc, copper and magnesium concentrations increased by 29.4 (p < 0.05), 69.0 (p < 0.001) and 48.7% (p < 0.001), respectively. Moreover, tea decoction treatment did not raise the reserve of zinc or copper significantly but it increased the reserve of magnesium stored in the liver (p < 0.05).

Black and green tea decoctions are popular beverages in Tunisia, especially after eating. Our study was performed to examine the effect of graded amounts of black and green tea decoction prepared under realistic Tunisian conditions on nonheme iron absorption from a typical Tunisian meal, ‘couscous’, by extrinsic radioiron labeling in rats. Concentrations of 300,200 and 100 µg/ml of black tea decreased dramatically nonheme iron bioavailability from couscous, but 50 µg/ml did not influence iron absorption. The inhibition of nonheme iron from couscous varied from 36 to 61% with black tea and 30.5% with green tea. Taken together, our findings show that the tea decoction in Tunisia has a great inhibitory power and may constitute an important factor for the development of iron deficiency anemia throughout Tunisia.

The aim of our study was to evaluate the bioavailability of iron from a typical Tunisian meal ‘couscous’ provided to healthy rats with or without appropriate mixtures of tea plus ascorbic acid and to search for the optimal amount of ascorbic acid able to overcome the inhibitory effect of tea prepared under realistic Tunisian circumstances. Our findings show that a tea decoction (100 mg/ml) reduced nonheme iron absorption from couscous by 50% (16.5 vs. 33.1%; p < 0.01). In contrast, administration of 20 mg ascorbic acid increased nonheme iron absorption from couscous by more than 100% (66.8 vs. 33.1%; p < 0.001). Administration of ascorbic acid (20 mg) in a tea decoction (100 mg/ml) completely counteracted the inhibiting effect of tea and significantly improved the nonheme iron absorption from couscous (34 vs. 33% in the control group; NS). The same effect was shown when 10 mg ascorbic acid was added to the tea decoction; however, 5 mg ascorbic acid was not able to overcome the inhibitory effect of tea on nonheme iron absorption from couscous (33.1 vs. 19.4%; p < 0.01). Our findings demonstrate that a molar ratio of ascorbic acid and tea equal or superior to 0.25 or 0.50 is necessary to overcome the inhibitory effect in rats of tea prepared under Tunisian circumstances. In relation to human nutrition, for Tunisians who regularly drink tea, we suggest a much greater amount of ascorbic acid than that normally recommended for normal subjects.

The influence of a diet of couscous with chickpeas, a traditional Tunisian meal, or one providing iron as ferrous sulfate, on the utilization of ⁵⁹Fe was evaluated in studies with rats. The iron content of the couscous and chickpea preparation was 30 mg/kg dry weight. There was no difference in the relative absorption of iron from ferrous sulfate or couscous with chickpeas, suggesting that iron from this preparation may be a good dietary source of nonheme iron for rats. Couscous and chickpeas consumption in Tunisia are estimated at 13.3 and 3.2 kg per capita/year, respectively. Our results in rats indicate that these foods could contribute a large proportion of an individual’s iron requirement. We conclude that the plant foods, especially the chickpeas, can be excellent sources of dietary-available iron.

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