What iron does in your body

Iron is a mineral your body uses to make hemoglobin, a protein in red blood cells that carries oxygen from your lungs to every other part of your body. Without enough iron, your red blood cells can't carry oxygen efficiently, which is why iron deficiency often leaves people feeling tired, weak, or short of breath even during normal activity.

Your body also uses iron to make myoglobin, a protein that stores oxygen in muscle tissue, and to support immune function and brain development. Iron is especially important during childhood, pregnancy, and menstruation, when your body's demand for it increases.

Key Takeaways

  • Iron carries oxygen through your blood and stores it in muscles, so low iron causes fatigue and weakness even when you're resting.
  • Red meat, poultry, fish, beans, leafy greens, and fortified cereals all contain iron, and your body absorbs iron from animal sources more easily than from plants.
  • Vitamin C helps your body absorb iron from food, so eating citrus, tomatoes, or bell peppers alongside iron-rich foods makes a real difference.
  • Too much iron can damage your heart, liver, and joints over time, so more is not better—your body needs a specific amount.
  • If you suspect low iron, a blood test from a doctor can measure your iron levels and rule out other causes of fatigue.

How much iron you need

The amount of iron your body needs depends on your age and sex. Adult men need 8 milligrams per day. Adult women aged 19 to 50 need 18 milligrams per day because menstruation causes iron loss. Women over 50 need 8 milligrams per day, the same as men. Pregnant people need 27 milligrams per day.

These numbers come from the National Institutes of Health and represent the amount most people need to stay healthy. Individual needs can vary based on health conditions, medications, and diet, so a doctor or registered dietitian can tell you whether your personal needs are different.

Iron-rich foods and how your body uses them

Iron comes in two forms: heme iron, which comes from animal sources and is absorbed easily by your body, and non-heme iron, which comes from plants and is absorbed less efficiently. Red meat, poultry, and fish contain heme iron. Beans, lentils, tofu, leafy greens like spinach and kale, and fortified cereals contain non-heme iron.

Your body absorbs heme iron at a rate of about 15 to 35 percent, meaning if you eat a serving of beef with 3 milligrams of iron, your body may absorb 0.5 to 1 milligram. Non-heme iron is absorbed at a rate of 2 to 20 percent, so the same 3 milligrams from beans might deliver only 0.06 to 0.6 milligrams to your body. This is why people who don't eat meat need to eat more iron-rich foods overall.

Vitamin C increases non-heme iron absorption significantly. Eating beans with tomato sauce, spinach with orange juice, or lentils with bell peppers helps your body pull more iron from the plant source. Coffee, tea, and calcium supplements can reduce iron absorption, so timing matters if you're trying to boost your intake.

Signs your iron might be low

Iron deficiency develops gradually, and early stages may cause no symptoms at all. As deficiency worsens, people often report fatigue that doesn't improve with rest, weakness, shortness of breath during normal activity, dizziness, pale skin, and cold hands and feet. Some people develop cravings for non-food items like ice, dirt, or starch—a condition called pica.

These symptoms can come from many other causes, including thyroid problems, sleep disorders, depression, or other nutritional deficiencies. A blood test is the only way to know whether low iron is the reason you feel tired. If you notice these symptoms, a doctor can order tests to measure your iron levels and identify what's actually going on.

When iron is too high

Your body has no built-in way to excrete excess iron, so iron accumulates over time if you consume too much. High iron levels can damage your heart, liver, pancreas, and joints. This can happen through repeated blood transfusions, certain genetic conditions like hemochromatosis, or long-term use of iron supplements at doses higher than recommended.

Taking iron supplements without a doctor's recommendation is not safer than taking too little—it's a different kind of risk. If you're considering iron supplements, a blood test first tells you whether you actually need them and at what dose. People with certain conditions, including some types of anemia and inflammatory bowel disease, should not take iron supplements without medical guidance.

Iron and pregnancy

During pregnancy, your blood volume increases by about 50 percent, which means your body needs significantly more iron to make extra hemoglobin. Pregnant people need 27 milligrams of iron per day, compared to 18 milligrams for non-pregnant women of the same age. Low iron during pregnancy is linked to premature birth and low birth weight.

Most prenatal vitamins include iron, and many doctors recommend iron supplements during pregnancy even if blood tests show normal levels, because the demands are so high. If you're pregnant or planning to become pregnant, your doctor can test your iron levels and recommend the right approach for your situation.

Getting iron from food versus supplements

Food sources of iron come with other nutrients your body needs, and your body naturally regulates how much iron it absorbs from food—you can't overdose on iron from eating. Supplements deliver a concentrated dose that bypasses this regulation, which is why they carry more risk of accumulation if taken long-term without monitoring.

If your blood tests show low iron, your doctor may recommend supplements for a set period, usually several months, to rebuild your stores. Once levels normalize, you can often maintain them through diet alone. Some people with chronic conditions that interfere with iron absorption may need ongoing supplements, but this should be monitored with regular blood tests.

Frequently Asked Questions

Can I get too much iron from eating red meat?

No. Your body absorbs only what it needs from food and excretes the rest through normal digestion. You can only accumulate excess iron through supplements, repeated transfusions, or genetic conditions that affect iron regulation. Eating iron-rich foods cannot cause iron overload.

Does spinach really have a lot of iron?

Spinach contains iron, but a famous myth overstated the amount decades ago. Raw spinach has moderate iron, and cooking it concentrates the iron slightly. However, spinach also contains oxalates, which reduce iron absorption, so your body doesn't use all the iron spinach provides. It's still a good iron source, especially when paired with vitamin C.

What if I'm vegetarian or vegan—can I get enough iron without meat?

Yes, but you need to eat more iron-rich plant foods and combine them with vitamin C to maximize absorption. Beans, lentils, tofu, fortified cereals, and leafy greens all contain iron. Eating these with citrus, tomatoes, or peppers helps your body absorb more. A doctor can test your iron levels to confirm you're meeting your needs.

Should I take an iron supplement if I feel tired?

Fatigue has many causes—sleep problems, thyroid issues, depression, and other nutritional deficiencies all cause tiredness. Taking iron without knowing your actual iron levels can mask a different problem or cause iron to accumulate. A blood test from a doctor can measure your iron and identify what's actually making you tired.

Can iron supplements cause constipation?

Yes. Iron supplements commonly cause constipation, nausea, and stomach upset. If a doctor recommends iron supplements, tell them about any side effects—they may adjust the dose, recommend taking it with food, or suggest a different form that's easier on your stomach. Don't stop taking prescribed supplements without talking to your doctor first.