Ferric orthophosphate iron absorption from a fortified cocoa drink in people and rats
What it found
In people who had fasted, iron from ferric orthophosphate was absorbed just as well as iron from ferrous sulphate when added to a malted cocoa drink.
Adding a small amount of vitamin C did not increase absorption further.
What they found
Studies in people
Iron absorption in people
People who fasted overnight absorbed about the same proportion of iron from the drink whether it contained ferric orthophosphate or ferrous sulphate. The average proportions absorbed were 0.24 and 0.23 respectively.
Vitamin C made no difference
Adding 20 mg of vitamin C to the drink did not improve iron absorption in people. The average proportion absorbed was 0.25 with vitamin C and 0.24 without it.
Animal and lab studies
Fasting boosted absorption in rats
Rats given the drink on an empty stomach absorbed more than twice as much iron as rats given the drink shortly after eating a small meal.
Meals affected the two salts differently
When rats ate a small meal before the drink, iron from ferrous sulphate was better absorbed than iron from ferric orthophosphate. On an empty stomach, both salts were absorbed equally well.
Other findings
Solubility in acid
The specific ferric orthophosphate used in this study dissolved completely in dilute hydrochloric acid, which mimics stomach acid.
What the authors conclude
- They conclude that the ferric orthophosphate used in the drink was absorbed as well as ferrous sulphate when people had fasted.
- They note that the high absorption levels seen in the human volunteers likely reflected the fact that they had empty stomachs.
- They advise that the amount of vitamin C added was too small to improve iron availability any further.
How it was done
Ferric orthophosphate is often used to add iron to foods because it does not change their colour or taste, but it is commonly thought to be poorly absorbed compared to other iron salts. The authors wanted to measure how much iron people actually took in from a cocoa drink fortified with this ingredient, and whether adding vitamin C helped.
Eleven healthy adults drank a malted cocoa powder mixed with hot water and fortified with either ferric orthophosphate or ferrous sulphate, after fasting overnight. Researchers measured unabsorbed iron in their stools over several days. They also tested iron absorption in rats, comparing those that fasted with those that ate a small meal first.
What it can’t tell you
- The human part of the trial only tested the drink after an overnight fast, so it cannot show what happens when people drink it with meals.
- The rat tests suggest absorption would drop after food, but animal digestion differs from ours.
- This small trial of eleven people may not represent everyone.
The paper
- Title
- Iron absorption from a malted cocoa drink fortified with ferric orthophosphate using the stable isotope 58Fe as an extrinsic label
- Type
- Randomised controlled trial
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Fairweather-Tait SJ, Minski MJ, Richardson DP (1983). Iron absorption from a malted cocoa drink fortified with ferric orthophosphate using the stable isotope 58Fe as an extrinsic label. The British journal of nutrition. doi:10.1079/bjn19830071Free full textPubMed 6882732DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error