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I recently discovered that iron we get from plants is not absorbed the same way as from meat, it is actually not the exact same iron: nonheme iron (plants) and heme iron (animals).

Things can enhance or inhibit the nonheme iron absorption (vitamin C enhances, phytate inhibits, coffee/tea inhibit...), as listed in this answer.

Many people drink tea or coffee on a regular basis.
How much does it inhibit the iron absorption? Those articles it recommend to not drink coffee/tea with your meal, but 1h later/before?

I read that it is also dependent on the quantity of coffee/tea, how? Should we limit at a given quantity?

  • 2
    I think it depends on the type of tea, at least. Spearmint for example contains several vitamins and minerals, including iron. If you drank a cup of mint tea then, it could only enhance absorption, since it contains the mineral itself. – expialidocious Mar 1 '18 at 4:42
  • Yes. Can you ask about a specific kind of beverage, or rephrase your question? – Turion Mar 1 '18 at 20:39
  • Well I just read this information about coffee and tea without specific distinction about the different types of tea, it just said that this is related to the tannin (so wine is also in the list). It probably depends on the quantity of tannin in the beverage, but I am not asking for a specific tea, I'd like to know the link between these beverages containing tannin and the iron absorption. – ymoreau Mar 2 '18 at 14:07
  • @expialidocious I guess it's not because the tea contains iron that your body will process it, if on the other hand the tea contains inhibitors, am I wrong ? – ymoreau Mar 2 '18 at 14:09
  • If it's related to tannins, then "tea" in this context has probably been brewed from Camellia sinensis, not "any beverage made by steeping something vegetal" :) – Erica Mar 2 '18 at 14:30
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Tea and coffee are well known as inhibitors of iron absorption, because both contain caffeine, polyphenols and phytates. Morck et al (1983) studied the effect of coffee on iron absorption in healthy humans. The main findings were:

  • The inhibitory effect increases with concentration. A cup of coffee ingested with a meal resulted in a reduction in absorption from 6% to 1%, and when the strength of coffee was doubled, absorption fell to 0.5%. It is not likely that the relationship is linear.
  • When ingested 1 hour before a meal, no decrease in absorption was found
  • When ingested 1 hour after a meal, the same decrease in absorption was found

Thus it is fair to say that any amount of coffee could reduce iron absorption. Actual iron absorption is obviously dependent on many other factors, in particular the presence of vitamins C and A, both of which can enhance iron absorption.

References:

T A Morck, S R Lynch, J D Cook; Inhibition of food iron absorption by coffee, The American Journal of Clinical Nutrition, Volume 37, Issue 3, 1 March 1983, Pages 416–420, https://doi.org/10.1093/ajcn/37.3.416

  • Thank you for the great answer, it is interesting to see that if ingested before a meal there is no effect. What could be interesting then would be to know for how many hours the post-meal coffee causes the decrease (1h after same level, but what about 2h, 4h etc). – ymoreau May 7 '18 at 7:06

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