Update: Vitamin C and Iron

I have been reviewing the research on iron and vegetarians (lacto-ovo and vegan). It appears that the iron status of vegetarian men is fine, but that, roughly, about 10% of vegetarian women have iron deficiency anemia and another 15 to 40% have low iron stores. These rates are not much different than the meat-eating women in the same studies.

From the research I’ve reviewed, vitamin C appears to be the most important factor in absorbing plant iron. I have added a few paragraphs to the Iron page at and am reproducing that section here:

“In meat, 65% of iron is bound to the heme molecule (from hemoglobin and myoglobin), which is relatively easily absorbed. The rest of the iron in meat and all iron in plants is non-heme iron. Non-heme iron requires being released from food components by hydrochloric acid and the digestive enzyme pepsin in the stomach. Non-heme iron also needs to be shuttled from the digestive tract into the bloodstream by a protein called transferrin.

“The phytates, found in legumes and grains, and polyphenols (including tannins found in coffee and green and black tea), can inhibit the absorption of plant iron. On the other hand, vitamin C is a strong enough enhancer of plant iron and can overcome the inhibitors in plant foods.

“One study found that various doses of phytate reduced iron absorption by 10 to 50%. But adding 50 mg of vitamin C counteracted the phytate, and adding 150 mg of vitamin C increased iron absorption to almost 30%. Similarly, in the presence of a large dose of tannic acid, 100 mg of vitamin C increased iron absorption from 2 to 8% (13).

“In another study, vegetarian children with iron deficiency anemia and low vitamin C intakes in India were given 100 mg of vitamin C at both lunch and dinner for 60 days. They saw a drastic improvement in their anemia, with most making a full recovery (2).

“Researchers used 500 mg of vitamin C twice daily after meals to increase hemoglobin and serum ferritin in Indian vegetarians. They concluded that vitamin C was more effective at increasing iron status than iron supplements (12).

“Vitamin C is found in citrus fruits, strawberries, green leafy vegetables (broccoli, kale, collards, Swiss chard, Brussels sprouts), bell peppers (yellow, red, and green), and cauliflower.

“Calcium supplements, coffee, and black and green tea inhibit iron absorption if eaten at the same time as iron, so avoid them at meals in which you are trying to increase iron absorption.”


2. Seshadri S, Shah A, Bhade S. Haematologic response of anaemic preschool children to ascorbic acid supplementation. Hum Nutr Appl Nutr. 1985 Apr;39(2):151-4. (Link)

12. Sharma DC, Mathur R. Correction of anemia and iron deficiency in vegetarians by administration of ascorbic acid. Indian J Physiol Pharmacol. 1995 Oct;39(4):403-6. PMID: 8582755. (Abstract only)

13. Siegenberg D, Baynes RD, Bothwell TH, Macfarlane BJ, Lamparelli RD, Car NG, MacPhail P, Schmidt U, Tal A, Mayet F. Ascorbic acid prevents the dose dependent inhibitory effects of polyphenols and phytates on nonheme-iron absorption. Am J Clin Nutr. 1991 Feb;53(2):537-41. PMID: 1989423.

4 Responses to “ Update: Vitamin C and Iron”

  1. Leo Says:

    Hey Jack,

    You state that calcium supplements inhibit iron absorption – does this mean that calcium from foods does not have the same effect? Does calcium in fortified plant milks inhibit iron absorption?

    Thank you!

  2. Jack Norris RD Says:


    > does this mean that calcium from foods does not have the same effect? Does calcium in fortified plant milks inhibit iron absorption?

    I don’t know of research showing that calcium from foods doesn’t inhibit iron absorption but that said, the thinking is that it’s only a problem for supplements.

  3. Leo Says:

    Okay. So does the calcium in fortified plant milk inhibit iron absorption? My guess is that it does, since the added calcium is a supplement the way I see it. I mean, why would the iron absorption be different when drinking plant milk fortified with calcium, as opposed to drinking non-fortified plant milk and taking a calcium supplement at the same time?

    Thank you once again for responding!

  4. Jack Norris RD Says:


    What you should realize is that everything in nutrition is about percentages and probability. Nutrient absorption, in particular, is rarely all or nothing. My guess is that the amount of calcium in fortified soymilk would decrease iron absorption a bit, but since it’s consumed with a large amount of other molecules, it would not be nearly as bad as a direct calcium supplement. I don’t imagine much of this has been tested – it’s mostly theoretical. If you are not prone to iron deficiency, then I would definitely not worry about the calcium in fortified soymilk. But if you are, then that’s a slightly different story, though there are other strategies that are going to do more for you than avoiding fortified soymilk. See the Summary here:

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