Dietary Iron and Iron Supplements

Medically Reviewed by Zilpah Sheikh, MD on July 18, 2024
Written by R. Morgan Griffin
9 min read

Iron is a mineral that's necessary for life. It plays a key role in making red blood cells, which carry oxygen. If you don't have enough iron, you may get iron-deficiency anemia, a low level of red blood cells. You can get iron from food and from supplements. Most people in the U.S. get enough iron from their diet and don't need supplements. But if a blood test shows your iron levels are low, your doctor might recommend an iron supplement. 

Natural food sources of iron include:

  • Meat, fish, and poultry
  • Dark leafy greens like kale and spinach
  • Whole grains
  • Tofu
  • Dried fruits 
  • Nuts and seeds
  • Seaweed
  • Beans, lentils, and peas

Iron from animal sources – called heme iron – is absorbed better by the body. This is why some vegans and vegetarians may have trouble getting enough iron. You can help your body absorb plant-based iron – called non-heme iron – by eating it with a source of vitamin C, such as fruit or vegetables like red bell peppers, kiwis, and oranges.

Iron supplements are often used to treat iron-deficiency anemia caused by:

You may be at risk of iron deficiency and benefit from iron supplements if you:

  • Menstruate, especially if the periods are heavy
  • Are pregnant, recently have given birth, or are nursing
  • Have had a major surgery or injury (trauma) that caused you to lose a lot of blood
  • Have diseases that affect their gastrointestinal (GI) system, such as ulcerative colitis
  • Have had gastric bypass surgery or a similar procedure
  • Eat a vegan or vegetarian diet

Children who drink more-than-recommended amounts of cow’s milk (more than 24 ounces a day) are also at risk of iron deficiency.

It's not as common, but you are also at risk of low iron if you:

  • Give frequent blood donations
  • Have frequent blood loss from nosebleeds
  • Have blood loss from hemorrhoids, gastritis, and other issues in the GI tract
  • Lose blood from your kidneys or bladder
  • Have a condition called intravascular hemolysis, which breaks down red blood cells, causing iron to leak out

If you have symptoms of iron-deficiency anemia, check with your doctor before you start taking supplements on your own, though, because it’s important to find out why you have low iron levels.

The most common effects of low iron are:

  • Fatigue
  • Being pale
  • A hard time breathing
  • Chest pain
  • A fast heartbeat
  • Feeling dizzy
  • Headaches
  • Feeling cold, especially your hands and feet
  • Getting frequent infections
  • Feeling like you want to eat things that aren’t food, like ice or dirt
  • Having restless legs, feeling like you constantly have to move them

You can also have low iron and not have any symptoms at all.

There are a few types of iron dietary supplements that your doctor might suggest or prescribe.

Ferrous sulfate is the most commonly prescribed iron supplement. Your doctor might recommend that you also take vitamin C along with the iron to help your body absorb the iron better. 

Ferrous gluconate does the same thing as ferrous sulfate, but it has less iron in each tablet. Because of the lower iron levels, some people believe that ferrous gluconate is absorbed better than other types of iron salts.

Ferrous fumarate is another readily available iron supplement that does the same thing as ferrous sulfate and ferrous gluconate but has a different chemical mix. Some people who have side effects from the other types of iron supplements may have fewer side effects with ferrous fumarate.

Ferric citrate is an iron supplement your doctor may give you if you’re on dialysis for chronic kidney disease (CKD) and your body is having trouble controlling the phosphorus levels in your blood. People with CKD who aren’t on dialysis might also get ferric citrate if they have iron deficiency anemia. Ferric citrate is only available by prescription.

If your iron deficiency is severe, your doctor might recommend an intravenous (IV) iron.

Are liquid iron supplements absorbed better than iron tablets?

You can get iron supplements in pill and liquid forms, but one doesn’t work any better than the other. Children and people who have trouble swallowing pills may find it better to use the liquid forms of iron supplements. Just be careful with measuring how much of the liquid iron supplement you use. Don’t use a kitchen measuring spoon, as these spoons aren’t accurate enough. Only use the dropper that comes with the bottle or a dosing syringe.

The recommended dietary allowance (RDA) includes the iron you get from both the food you eat and any supplements you take.

Category

Recommended Dietary Allowance (RDA)

CHILDREN

7-12 months

11 milligrams (mg)/day

1-3 years

7 mg/day

4-8 years

10 mg/day

9-13 years

8 mg/day

FEMALES

14-18 years

15 mg/day

19-50 years

18 mg/day

51 years and over

8 mg/day

Pregnant

27 mg/day

Breastfeeding 

Under 19 years: 10 mg/day

 

19 years and over: 9 mg/day

MALES

14-18 years

11 mg/day

19 years and up

8 mg/day

Strict vegetarians may need to take in higher levels of iron.

At high doses, iron is toxic. For adults and children ages 14 and up, the upper limit – the highest dose that can be taken safely – is 45 milligrams a day. Children under age 14 should not take more than 40 milligrams a day.

The American Academy of Pediatrics suggests that – starting at 4 months of age – full-term, breastfed infants should be supplemented each day with 1 milligram of oral iron per kilogram of body weight. This should continue until iron-containing complementary foods, such as iron-fortified cereals, are added to the diet. Standard infant formula that contains 12 milligrams per liter of iron can fulfill the iron needs of an infant until age 1.

Ask your health care provider how much iron supplement you or your child should take, if any.

Like all supplements and medications, iron can cause side effects in some people.

Even taken at normal doses, the most common side effect of oral iron supplements is constipation. Making sure you drink plenty of water throughout the day may keep this from happening. 

Stomach problems

Iron can irritate the lining of your gastrointestinal (GI) tract. It can also change the microbiota in your GI tract, which is the balance of good and bad bacteria.

This can cause effects like:

  • Upset stomach
  • Decreased appetite
  • Nausea
  • Diarrhea
  • Stomach cramps
  • Dark poop 

Although most iron supplements work better if you take them on an empty stomach, this can make the side effects worse because there is nothing to protect your GI tract lining from the irritation. If this is the case for you, speak with your doctor about how best to take your supplement.

If you do take it with food, be sure not to take it with:

  • Milk
  • Caffeine
  • Antacids
  • Calcium supplements

Problems with zinc absorption

Your body needs zinc to help your immune system and your metabolism. If you take iron supplements, this could decrease the amount of zinc your body absorbs from your food. Blood tests can show if your levels of zinc are too low. If you are worried about this, speak with your doctor.

Risks of iron overdose

It’s important to take only the amount of iron your doctor prescribes or what is on the supplement’s label. Don’t take more than that unless your doctor tells you to. Too much iron can cause iron poisoning, which can lead to liver damage and death. The first symptoms of iron poisoning include:

  • Vomiting
  • Diarrhea
  • Belly pain

Iron overdose is a common cause of poisoning in children. It can be fatal. Signs of an iron overdose include severe vomiting and diarrhea, stomach cramps, pale or bluish skin and fingernails, and weakness. Treat these signs as a medical emergency. Call poison control and get medical help right away.

Iron can interact with many drugs and supplements, including antacids and proton pump inhibitors, some  antibiotics, calcium, and more. Here are some examples:

  • Amphetamine
  • Cefuroxime axetil
  • Digoxin
  • Magnesium sulfate
  • Phenytoin

Be sure your doctor is aware of all of the prescription and over-the-counter medicines you take if they suggest you take an iron supplement.

Whenever possible, it’s best to get your nutrients through a healthy diet because the vitamins and minerals are strongest and most effective when you consume them naturally. That said, some people can’t absorb the nutrients from foods, especially if they have a GI disorder, like Crohn’s disease or a malabsorption syndrome, that makes their gut unable to get the nutrients.

How long you should take an iron supplement depends on what is causing your iron deficiency and how well the supplements work. After you’ve been taking the iron for 1 to 4 weeks, you probably will start feeling better. Your doctor may recommend another blood test to see if there is any improvement.

If the supplements are helping, you would usually continue to take them for up to 6 months. Your doctor will likely check to see if your iron level stays normal.

If you have a long-term (chronic) illness that is causing the iron deficiency, you may need to take the supplements for a long time.

It’s not uncommon to be iron deficient. It can be caused by blood loss (heavy or long-term bleeding), not having enough iron in your diet, or having an illness that prevents your body from absorbing iron from your food. If you need iron supplements, speak with your doctor to see how much iron you need to take and for how long. Taking too much iron can lead to a serious complication called iron poisoning.

Is it OK to take an iron supplement every day?

Many people do take daily iron supplements, but you should speak with your doctor before starting yourself. You may not need the extra iron or, if you do, you might be able to get it through your food.

What is the best form of iron to take?

Iron is always best if it comes from your diet.

Is there any downside to taking iron supplements?

Taking iron supplements can cause digestive problems. Taking too much can also lead to iron overdose and poisoning. 

How do I know if my iron is low?

You may have some symptoms, like pale skin and fatigue, if your blood iron is too low. The best way to tell is through a blood test that measures your blood iron level.

What should be avoided when taking iron?

There are some medications that will prevent your body from absorbing the iron properly. Before taking the iron supplements, make sure your doctor knows what other medications you take. If you’re using an OTC supplement, speak to your pharmacist about your current drugs and the supplement you want to take. You also shouldn’t take iron supplements with:

  • Milk
  • Caffeine
  • Antacids
  • Calcium supplements