I was reading a few abstracts about this, myself (being at dietary risk for iron deficiency, as a vegetarian, and they say that tea has been known to affect those who need iron supplements too).
Impact of tea drinking on iron status in the UK: “From the available evidence there is no need to advise any restriction on tea drinking in healthy people with no risk of iron deficiency. In groups at risk of iron deficiency the advice should be to drink tea between meals and to wait at least 1 h after eating before drinking tea”.
A 1-h time interval between a meal containing iron and consumption of tea attenuates the inhibitory effects on iron absorption: “This study shows that tea consumed simultaneously with an iron-containing porridge meal leads to decreased nonheme iron absorption and that a 1-h time interval between a meal and tea consumption attenuates the inhibitory effect, resulting in increased nonheme iron absorption. These findings are not only important in relation to the management of iron deficiency but should also inform dietary advice, especially that given to those at risk of deficiency”.
Effect of tea and other dietary factors on iron absorption: “Recommendations with respect to tea consumption (when in a critical group) include: consume tea between meals instead of during the meal; simultaneously consume ascorbic acid”.
The effect of tea on iron absorption: “Drinking tannin-containing beverages such as tea with meals may contribute to the pathogenesis of iron deficiency if the diet consists largely of vegetable foodstuffs”.
The Impact of Tannin Consumption on Iron Bioavailability and Status: “Single-meal studies with hydrolyzable and oligomeric catechin and epicatechin tannins (tea and tannic acid) generally support reductions in bioavailability related to tannin consumption but not consumption of condensed tannin, which are more commonly found in food”.
Excessive tea consumption can inhibit the efficacy of oral iron treatment in iron-deficiency anemia: “Intestinal absorption of non-heme food iron may be inhibited by tea, which, on the contrary, does not exert any appreciable effect on heme iron assimilation. Therefore, while an iron-deficiency anemia cannot develop in non-vegetarian subjects as a consequence of tea consumption only, it is possible that tea could inhibit the therapeutic effect of oral iron drugs, which are usually non-hemic ferrous salts, in iron-deficient subjects”.
Iron deficiency anemia due to excessive green tea drinking: “Tea interferes with iron absorption and can lead to iron deficiency anemia when consumed in large quantities. The rechallenge effect of green tea on anemia in a middle-aged man emphasizes the potential causal role of this beverage. Lifestyle and dietary habits are important diagnostic considerations in diseases of this type”.
Effect of tea on 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”
Actually, I was reading about couscous there, then lots of tea. This is kind of interesting, by the way: Comparative effects of couscous and pasta on glycemia…