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NUTRITION HOTLINE.

This issue's Nutrition Hotline addresses whether drinking black tea every day can interfere with iron absorption.

QUESTION: I drink several cups of black tea every day. Recently, I found out that I'm anemic, and my doctor told me to stop drinking tea because it could be interfering with iron absorption. Do I really need to give up my tea? E.K. via e-mail

ANSWER: The form of iron in vegan diets is non-heme iron, which simply means "iron that doesn't come from blood." Non-heme iron's absorption is subject to interference by phytates (see Vegetarian Journal, Issue 1, 2017) and polyphenols. Black tea contains polyphenols, as do coffee, green tea, herb tea, red wine, and cocoa. (1) Polyphenols prevent the non-heme iron from moving from the intestines into the blood. The iron stays in the intestines and is ultimately excreted. Black tea has at least twice as high a concentration of polyphenols as do herb teas or green tea. (2)

In studies where subjects drank black tea along with their meal, between 79 and 94 percent of the iron in the meal was not absorbed.1 Peppermint tea was similar to black tea in terms of markedly interfering with iron absorption; other herb teas, such as chamomile tea, had less of an effect. (1) Herb teas and green teas have a lower polyphenol concentration than black teas. (2)

A recent study examined the timing of tea drinking on iron absorption. Drinking black tea an hour after finishing a meal substantially reduced the effect of tea on iron absorption. (3) In other words, waiting for an hour after a meal to drink tea allowed more iron from the meal to be absorbed. The researchers only tested the effect of waiting an hour so we can't know if it would be better to wait even longer or if waiting a lesser amount of time would also be effective. Another study found that drinking tea an hour before a meal reduced the polyphenol effect. (4)

Based on these results, there are several things that you can do instead of giving up tea. You could drink black tea at least an hour before starting or an hour after completing a meal or snack. You could switch to herb tea (other than peppermint), knowing that there would still be some interference with iron absorption, or you could drink herb tea at least an hour before or after a meal. Cheers!

References:

(1) Hurrell RF, Reddy M, Cook JD. 1999. Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages. Br J Nutr. 81:289-295.

(2) Hallberg L, Hulthen L. 2000. Prediction of dietary iron absorption: an algorithm for calculating absorption and bioavailability of dietary iron. Am J Clin Nutr. 71:1147-1160.

(3) Ahmad Fuzi SF, Koller D, Bruggraber S, et al. 2017. A 1-h time interval between a meal containing iron and consumption of tea attenuates the inhibitory effects on iron absorption: a controlled trial in a cohort of healthy UK women using a stable iron isotope. Am J Clin Nutr. 106:1413-1421.

(4) Disler PB, Lynch SR, Torrance JD, et al. 1975. The mechanism of the inhibition of iron absorption by tea. S Afr J Med Sci. 40:109-116.

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Title Annotation:health impact of drinking black tea
Author:Mangels, Reed
Publication:Vegetarian Journal
Date:Jul 1, 2018
Words:534
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