Ascorbic acid and how it changes iron absorption from food
What it found
Ascorbic acid strongly increased the amount of nonheme iron absorbed from meals in people.
It worked by keeping iron dissolved so the gut could take it in.
What they found
Studies in people
More iron absorbed
Adding 100 ml of orange juice with 40 to 50 mg of ascorbic acid to a breakfast meal raised iron absorption from 3.7% to 10.4% in people. Another study found that 70 mg of ascorbic acid made absorption two and a half times higher.
Blocks tea interference
Tea normally stops the body from taking in iron from grain-based meals. Ascorbic acid reversed this blocking effect in people, and more ascorbic acid meant more iron was absorbed even when tea was present.
Less effect with meat
Meat already helps the body absorb iron. When people ate meals containing beef or fish, adding 100 mg of ascorbic acid gave a smaller extra boost than it did for vegetable-only meals.
Dirt and rust iron
Iron from soil or cooking pots is very hard for the body to use. Adding 100 mg of ascorbic acid to a meal raised absorption of this type of iron in people, but the total amount taken in remained very low.
Amount needed matters
In people, the boost to iron absorption rose in step with the amount of ascorbic acid added, up to about 100 mg. Beyond that point, adding more ascorbic acid gave a much smaller extra benefit.
Animal and lab studies
How it works chemically
In lab tests, ascorbic acid bound to iron in acidic conditions and kept it dissolved even when the liquid became alkaline. In rats, iron mixed with ascorbic acid before becoming alkaline was absorbed much better than iron mixed after.
What the authors conclude
- They conclude that ascorbic acid is the strongest known food factor for boosting iron absorption from plant foods.
- They note that its high cost and tendency to break down during food storage make it difficult to use widely in fortification programs.
- They suggest that while large daily doses of ascorbic acid increase iron absorption, the actual long-term effect on body iron stores may be modest.
How it was done
Most of the iron in a typical diet is nonheme iron, which the body absorbs poorly compared to iron from meat. The authors wanted to understand how ascorbic acid might help the body take in more of this plant-based iron to fight iron deficiency.
The researchers studied iron absorption in people eating test meals made from grains like maize, wheat, rice, or soy, sometimes with added meat or fish. They measured how much iron was taken up when different amounts of ascorbic acid were included. They also ran lab tests on iron solutions and studies in rats to see how ascorbic acid changed iron at different acidity levels.
What it can’t tell you
- These short feeding trials measure how much iron enters the body from a single meal.
- They cannot show whether eating ascorbic acid regularly prevents or treats iron deficiency over months or years.
The paper
- Title
- Interaction of vitamin C and iron
- Type
- Study
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Lynch SR, Cook JD (1980). Interaction of vitamin C and iron. Annals of the New York Academy of Sciences. doi:10.1111/j.1749-6632.1980.tb21325.xFree full textPubMed 6940487DOI
Summary written 1 Oct 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error