Iron Supplement With Vitamin C: What to Know

Quick answer

Vitamin C raises how much nonheme iron the body absorbs, the kind found in plants, fortified foods and most supplements. In a study of 34 women with low iron stores, 80 mg of vitamin C raised absorption of a 100 mg iron dose by 30%, and 500 mg added nothing more. People with hemochromatosis should avoid both supplements.^1,2

Key facts

NIH says vitamin C raises the absorption of nonheme iron, the form in plant foods, fortified foods and most supplements.^1,3
In 34 women with low iron stores, 80 mg of vitamin C raised absorption of a 100 mg iron dose by 30%, and 500 mg added nothing more. Coffee cut absorption by 54%.²
The body absorbs about 14% to 18% of the iron in mixed diets with meat, seafood and vitamin C, and 5% to 12% in vegetarian diets, but in a typical Western diet the difference is small for most people.^3,4
Women aged 19 to 50 need 18 mg of iron a day and men 8 mg. Adults need 75 to 90 mg of vitamin C.^5,6
The upper limit for iron is 45 mg a day from food and supplements, set to avoid stomach and bowel side effects. For vitamin C it is 2,000 mg.^6,7

Two kinds of iron and one helper

Iron in food comes in two forms. Heme iron, in meat, seafood and poultry, is absorbed well on its own. Nonheme iron, in plants, fortified foods and most supplements, is absorbed less well, and that is the form vitamin C acts on. Hepcidin, a hormone, also governs how much iron the gut takes in at all.^3,7

Eating foods that contain vitamin C at the same meal as plant sources of iron helps the body absorb more of that iron.^1,5

Vitamin C, meat, poultry and seafood help the body absorb nonheme iron, while phytate in grains and beans and some polyphenols reduce it. In a varied Western diet these effects are small for most people.^3,7

The numbers explain why the effect is real but easy to overstate. A mixed diet with meat, seafood and vitamin C gives about 14% to 18% iron absorption. A vegetarian diet gives 5% to 12%. NIH adds that in a typical Western diet these effects make little difference to most people's iron status.^3,4

What each is graded for

Increases iron absorption*^1,4,5,8

Moderate evidence

A well-established nutrient function, permitted in this wording by EU regulators for foods that are at least a source of vitamin C. NIH says vitamin C raises absorption of nonheme iron, the form in plant foods and fortified foods, and that mixed diets with meat, seafood and vitamin C let the body absorb about 14% to 18% of their iron, against 5% to 12% for vegetarian diets. In a typical Western diet these effects make little difference to most people's iron status.

Amount studied: Vitamin C eaten in the same meal as plant sources of iron

Needed to make hemoglobin, which carries oxygen in red blood cells, and myoglobin, which supplies oxygen to muscles*^3,7

Moderate evidence

A long-established role of the mineral, described by NIH. Iron is also needed for growth, development and making some hormones. This does not mean extra iron helps people who already get enough, and most people in the US do.

Amount studied: Recommended intake: 8 mg a day for men and for women over 50, 18 mg for women aged 19 to 50

Helps women who menstruate build hemoglobin and iron stores*^3,7,9

Strong evidence

A Cochrane review of 67 randomized trials in 8,506 women who menstruate found that daily iron raised hemoglobin (51 trials, 6,861 women, high-quality evidence) and iron stores, and made low iron less common. Women aged 19 to 50 need 18 mg a day, against 8 mg for men, because menstruation adds to their iron losses. Iron also roughly doubled reports of stomach and bowel side effects in these trials.

Amount studied: Daily iron tablets taken at least five days a week; the amount varied between trials

What the studies found about taking them together

The most useful study for this question measured absorption directly in 34 women with low iron stores. It tested vitamin C, coffee, breakfast and time of day, one change at a time. These are findings from a single small study, not rules.²

In the same study, taking the dose with 80 mg of vitamin C raised absorption by 30%, and 500 mg of vitamin C added nothing more.²

Coffee taken with the dose cut absorption by 54%, and a breakfast with coffee and orange juice cut it by 66%.²

In a study of 34 women with low iron stores, a 100 mg dose taken in the afternoon was absorbed 37% less than the same dose taken in the morning, a difference that just missed statistical significance.²

Two more findings come from other studies in women with low iron stores. Large doses raise hepcidin, so doses of 60 mg or more cut absorption of the next day's dose by 35% to 45%, and 60 mg taken on alternate days was absorbed better than on consecutive days. In a separate 6-month trial of 100 mg doses, alternate days caused fewer stomach and bowel side effects than daily dosing.^10,11,12

Calcium might reduce iron absorption, although this has not been firmly established, so experts suggest taking calcium and iron supplements at different times of day.^3,7

Amounts and our products

Iron and vitamin C for adults, per day^1,3,6,7,13
	Iron	Vitamin C
Recommended amount	8 mg for men and for women over 50; 18 mg for women aged 19 to 50	75 mg (women), 90 mg (men)
In pregnancy	27 mg	85 mg
Upper limit	45 mg from food and supplements	2,000 mg from food and supplements
Supplement amounts	Multivitamins with iron usually 18 mg; iron-only often 65 mg	Absorption falls for single doses of 500 mg or more
Groups with different needs	People who eat no meat, poultry or seafood need about 1.8 times as much	People who smoke need 35 mg more

We do not sell an iron supplement, so only vitamin C appears in the card below. If you take iron from another source, count the vitamin C in our products as part of the same meal.

What’s in ours

Men's Multi: Vitamin C, 150 mg per serving, from the label
Immune Support: Vitamin C, 180 mg per serving, from the label

Overload, children and who should ask first

People with hereditary hemochromatosis absorb too much iron, which builds up to toxic levels. NIH advises them to avoid iron and vitamin C supplements.^3,7

In people with hereditary hemochromatosis, high doses taken for a long time could worsen iron overload and damage tissues. NIH says people with this condition should avoid vitamin C supplements.^1,5

Accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6. Iron tablets and capsules must carry a warning to keep them out of children's reach and to call a doctor or poison control center after an accidental overdose.^3,7

High doses of iron supplements, especially on an empty stomach, can cause upset stomach, constipation, nausea, abdominal pain, vomiting and diarrhea. Doses of 45 mg a day or more are the most likely to cause them.^3,7

Ask your pharmacist how far apart to take them

Iron supplements can reduce how much levothyroxine the body absorbs and make it less effective. The levothyroxine label lists ferrous sulfate among products that may bind the medicine and says to take them apart; ask your pharmacist how to space them.^3,7,14,15

On the medicine's label

Ask your pharmacist how far apart to take them

Iron can keep tetracycline antibiotics such as doxycycline from being absorbed. The doxycycline label says iron-containing preparations impair the absorption of tetracyclines.¹⁶

On the medicine's label

Do not use iron if you have hereditary hemochromatosis or another iron overload condition. NIH advises people with hemochromatosis to avoid iron and vitamin C supplements.^1,3
Ask first if you have been told you have anemia. Its cause needs to be found, and extra iron does not help every type.³
Ask first if you are a man or past menopause and no one has told you that you need iron.³
Ask first if you take levothyroxine, levodopa, an antibiotic, dolutegravir or a medicine that lowers stomach acid.^3,7
Ask first if you are pregnant or planning a pregnancy, or have kidney disease or a stomach or bowel condition.³
Keep iron supplements out of children's reach. Accidental overdose is a leading cause of fatal poisoning in children under 6.⁷

Questions people ask

Should you take iron with vitamin C?

NIH says vitamin C raises absorption of nonheme iron, and in a study of women with low iron stores 80 mg of vitamin C raised absorption of a 100 mg dose by 30%. For a typical Western diet the effect is small, and people with hemochromatosis should avoid both.^1,2

How much vitamin C does it take?

In the one study that tested it, 80 mg raised iron absorption by 30% and 500 mg added nothing more.²

Does coffee affect iron absorption?

In the same study coffee taken with the dose cut absorption by 54%, and a breakfast with coffee and orange juice cut it by 66%.²

Can iron and vitamin C cause an upset stomach?

Both can. Iron doses of 45 mg a day or more are the most likely to cause constipation, nausea and abdominal pain, and high doses of vitamin C can cause diarrhea and cramps because unabsorbed vitamin C draws water into the gut.^1,7

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Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.