Iron: what it does, how much you need, and how much is too much
By Vita · fact-checked against NIH ODS
Vita is Vitaminico's AI nutrition coach. Every number here is checked against the NIH Office of Dietary Supplements; these pages have not yet been reviewed by our registered dietitians.
The mineral your blood uses to carry oxygen through your body.
Iron: key facts
- Everyday need (RDA/AI)
- 8 mg for men and for women 51+; 18 mg for women 19-50; 27 mg in pregnancy
- Safe upper limit (UL)
- 45 mg
- Measured in
- mg
- Best foods
- Lean meat and seafood (oysters), beans and lentils, nuts, spinach, iron-fortified cereals and breads
Adult values from the NIH ODS Iron fact sheet. Needs differ in pregnancy, lactation and childhood.
What does iron do?
Iron is a mineral your body uses to make hemoglobin, the protein in red blood cells that carries oxygen from your lungs to the rest of your body. It also makes myoglobin, which supplies oxygen to your muscles. Your body needs iron to produce some hormones and connective tissue as well.
Why you might be low on iron
- You have heavy menstrual periods, which lose blood (and iron) each month
- You are pregnant — your blood volume rises, so your needs jump to 27 mg a day
- You eat no meat, poultry, or seafood; the body absorbs nonheme iron from plants less well, so vegetarians need almost twice as much
- You donate blood frequently
- You have cancer, a GI disorder such as celiac or inflammatory bowel disease, or heart failure that causes blood loss or blocks absorption
Signs of low iron
These are common signals, not a diagnosis — a blood test and your clinician confirm a real gap.
- Tiredness and lack of energy
- Stomach and digestive (GI) upset
- Poor memory and trouble concentrating
- Getting sick more easily — less ability to fight off infections
- Feeling cold, or trouble controlling body temperature
- In infants and children, learning difficulties and delayed development
Best food sources of iron
| Food | Typical amount |
|---|---|
| Breakfast cereal, fortified with 100% of the Daily Value for iron | 18 mg per serving |
| Oysters, eastern, cooked | 8 mg per 3 oz |
| White beans, canned | 8 mg per 1 cup |
| Dark chocolate (45–69% cacao) | 7 mg per 3 oz |
| Beef liver, pan-fried | 5 mg per 3 oz |
| Lentils, boiled | 3 mg per ½ cup |
| Spinach, boiled | 3 mg per ½ cup |
How much iron is too much?
The tolerable upper intake level (UL) for adults is 45 mg per day. Supplemental doses of 45 mg or more can cause GI upset, and acute overdose is a leading cause of poisoning in young children; deficiency is the most common nutrient deficiency worldwide.
For adults the daily upper limit from food plus supplements is 45 mg; high supplement doses, especially on an empty stomach, can cause upset stomach, constipation, nausea, vomiting, and can lower zinc absorption. Extremely high doses can cause organ failure, and iron-containing products are a leading cause of fatal poisoning in children under 6, so keep supplements out of their reach.
Stacking a multivitamin, a single supplement and fortified foods adds up faster than it looks — run your full dose through the free Supplement Safety Checker before adding anything new.
Iron FAQ
Do I need to take an iron supplement?
Most people in the United States get enough iron from food and don't need one. Take iron only if a blood test or your doctor shows you're low, since getting too much can be harmful. Pregnant and breastfeeding people should follow the dose their obstetrician or provider recommends.
How do I get more iron from plant foods?
Your body absorbs plant (nonheme) iron better when you pair it with vitamin C — citrus, strawberries, sweet peppers, tomatoes, or broccoli — or eat it alongside meat, poultry, or seafood. If you eat no animal foods at all, you need almost twice as much iron.
Does anything block iron absorption?
Yes. Calcium can interfere, so take calcium and iron supplements at different times of day. Acid-reducing medicines like omeprazole (Prilosec) and lansoprazole (Prevacid) can also lower how much nonheme iron you absorb from food.
Source
Every RDA/AI, upper limit and unit on this page is drawn from the NIH Office of Dietary Supplements Iron fact sheet ›.
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Educational, not medical advice. The upper limits shown are Tolerable Upper Intake Levels for healthy adults from all sources combined; needs differ in pregnancy, lactation, childhood and with some conditions or medications. This page does not diagnose a deficiency or set your dose — talk to your clinician before starting any high-dose supplement.