Iron deficiency is the most widespread nutritional deficiency in the world, affecting approximately 14% of the American population, according to a 2024 study published in JAMA Network. If you’ve recently had your bloodwork done, it’s possible your doctor might have told you that you have low ferritin, low hemoglobin, low hematocrit, low serum iron and/or high transferrin — all of which can be indicators of iron-deficiency anemia, according to the American Society of Hematology. This can cause symptoms like extreme fatigue, brain fog, easy bruising and more.In this case, your doctor might have recommended you start taking an iron supplement. But for those who don’t have a set care plan when it comes to iron, it’s possible you might be taking too much ― or too little ― and not even know it. Ahead, we spoke with hematologists about how much iron you should really be taking per day, the benefits of iron supplementation, and how to tell if you’re taking too much. What causes low iron? “In general, low iron is either due to inadequate dietary intake, poor absorption of iron from food, or chronic blood loss,” said Dr. Thomas Platè, a hematologist with Sylvester Comprehensive Cancer Center in the University of Miami Health System. People with heavy menstrual periods, for example, can be at risk for low iron due to blood loss.Additionally, Dr. Adeel Khan, an academic hematologist, oncologist and epidemiologist in Dallas, added that patients with compromised gastrointestinal absorption, such as those who have had bariatric surgery, may also have low iron. “People with iron deficiency may feel tired, weak, short of breath, dizzy or have restless legs,” said Dr. Daniel Landau, an oncologist, hematologist and expert contributor at The Mesothelioma Center. “A blood test is the best way to know if iron is actually the problem.”Ekaterina Goncharova via Getty ImagesPeople who have heavy menstrual periods, gastrointestinal absorption issues and more may be low in iron.How much iron should you take per day? If you’ve learned you have low iron, it’s possible your doctor might start you on an iron supplement before discussing other treatment options. According to Platè, the dosing of iron supplements depends on age, the severity of the iron deficiency, the cause of the iron deficiency and pregnancy status, among other considerations.“For people with iron deficiency, a commonly recommended dose is 65 milligrams [of elemental iron] daily,” Platè said, noting that the elemental iron supplement should be in the form of ferrous sulfate.Additionally, pregnant individuals may benefit from around “27 mg of elemental iron supplement daily,” Platè said. But as always, chatting about your personal health factors with your doctor first is critical.Landau said one of the biggest misconceptions is that anyone who feels tired should take iron. “Fatigue has many causes, so it’s important to get tested and make sure iron deficiency is actually the issue before starting supplements,” Landau said. Additionally, Platè said certain conditions, such as thalassemia and myelodysplastic syndrome can mimic iron deficiency, but will not respond to iron supplementation so you’ll want to rule that out from the offset before starting this type of supplements. How much iron is too much? Any single dose more than 120 mg elemental iron is likely too much, according to Platè. Platè also added that it’s worth noting that taking iron more than once daily provides no additional benefit compared to once-daily or less frequent dosing for routine iron deficiency. “Older guidelines sometimes recommended taking iron up to three times per day, and this advice may still be encountered. However, no major U.S. medical organizations currently recommend oral iron more than once daily for most conditions, with the exception of iron deficiency in chronic kidney disease,” Platè said. The normal range for iron in male adults is 70 to 180 micrograms per deciliter. For women, the normal range is 60 to 170 micrograms per deciliter, according to Harvard Health. The best way to know if you’re taking too much is to look at your lab work. If your values fall out of those ranges, then it’s possible you’re taking too much (or too little) iron. Aside from knowing the numbers, there are also some physical symptoms you might notice and experience if you’re taking too much iron. “Common side effects include constipation, nausea, stomach upset and dark stools,” Landau said. Other side effects might include joint pain, low sex drive, unexplained weight loss and pain in your knuckles. What happens if you take too much iron?According to Platè, excessive iron intake over time can lead to iron overload accumulating in organs such as the heart and liver (also known as hemochromatosis).“Uncorrected iron overload can lead to major illnesses such as heart failure and cirrhosis,” he said. “And because the body has no natural mechanism to eliminate excess iron, treating iron overload is complicated and requires regular blood donation or expensive medications.” With this in mind, it is important to work closely with a doctor to monitor hemoglobin and ferritin levels if you’re taking iron supplementation to prevent uncomfortable symptoms and potentially dangerous side effects like those mentioned above.