Merck Manuals: Common Causes of Iron Deficiency Anemia - and How to Treat It

RAHWAY, N.J., May 8, 2025 /PRNewswire/ -- Nearly one-third of American adults may have an iron deficiency, leading to symptoms like trouble concentrating and fatigue. If left unchecked, iron deficiency can also lead to a more serious condition called iron deficiency anemia.

In a new editorial from MerckManuals.com, Gloria F. Gerber, MD, Johns Hopkins School of Medicine, Division of Hematology, addresses some common causes of iron deficiency and ways to treat it.

Cause #1 – General blood loss

In adults, iron deficiency is most commonly caused by loss of blood. This blood loss can come from several sources, says Gerber. A wound or trauma may lead to iron deficiency very quickly. In women who have menstrual periods, menstrual bleeding is often a cause of iron deficiency.

In men and postmenopausal women, iron deficiency can also indicate bleeding you can't see, says Gerber. This is most often in the digestive tract—for example, from a bleeding ulcer or a polyp in the colon. Chronic bleeding due to colon cancer can also lead to iron deficiency in middle-aged and older adults, says Gerber.

Cause #2 – Decreased absorption

Decreased iron absorption in the digestive tract, known as malabsorption, can result from various disorders, Gerber says. Celiac disease is a common disorder known to cause malabsorption. Other potential causes include bariatric surgeries and bowel removal, as well as rare genetic disorders.

Cause #3 – Inadequate diet/increased requirements

In the United States, anemia rarely results from consuming too little iron, because supplemental iron is added to many foods, says Gerber. But for some patients with increased iron requirements, a diet with limited iron can lead to iron deficiency and even iron deficiency anemia. Those who are pregnant often begin their pregnancy with mildly reduced stores of iron and have increased iron requirements.

Cause #4 – Dialysis

People on dialysis because of kidney failure, especially those taking erythropoietin (EPO) or other erythropoiesis-stimulating agents, can be at risk for iron deficiency. Typically, these individuals are closely monitored, says Gerber.

How Iron Deficiency Anemia is Diagnosed and Treated

Overall, it may be best to think of iron deficiency on a spectrum. Anemia may be the more serious outcome, but iron deficiency should be addressed even if a person is not yet anemic, says Gerber.

Anemia is diagnosed with routine blood work known as a blood count. Diagnosing iron deficiency is a little more challenging. People should make sure doctors know of any other medical conditions they have, as some could influence test results.

Once an iron deficiency is identified, treatment includes addressing the root cause and replacing the lost iron in the body. For some patients, an iron-rich diet (including foods such as meats, shellfish, dried fruits, cereals, leafy greens, and beans) may not be enough to replenish iron stores, and oral or intravenous supplementation could be needed. 

What to Know About Taking Oral Iron Supplements

Correcting iron deficiency anemia with oral iron supplements usually takes about 6 weeks, but may take longer to fully replete iron stores, even after a cause like bleeding has stopped. Iron supplements also have a reputation for leading to digestive issues including bloating, cramping, and constipation. The good news, says Gerber, is that some doctors will recommend taking the supplement every other day, which may help with absorption and reduce unpleasant side effects.

To read more of Gerber's insights on iron deficiency anemia, visit the editorial on MerckManuals.com.

About The Merck Manuals and MSD Manuals

First published in 1899 as a small reference book for physicians and pharmacists, The Merck Manual grew in size and scope to become one of the world's most widely used comprehensive medical resources for professionals and consumers. As The Manual evolved, it continually expanded the reach and depth of its offerings to reflect the mission of providing the best medical information to a wide cross-section of users, including medical professionals and students, veterinarians and veterinary students, and consumers. In 2015, The Manuals kicked off Global Medical Knowledge 2020, a global initiative with the goal to make the best current medical information accessible by up to three billion professionals and patients around the world by 2020. The Manuals achieved that goal, and today its medical information is available in nearly 250 countries and in 15 languages. It's continuing its ambitious mission through outreach, education and creating new reliable medical resources. For access to thousands of medical topics with images, videos and a constantly expanding set of resources, visit MerckManuals.com or MSDManuals.com and connect with us on social media: For Consumers in the U.S. and its territories: X (formerly Twitter) and Facebook. For Professionals in the U.S. and its territories: X (formerly Twitter) and Facebook

About Merck

At Merck, known as MSD outside of the United States and Canada, we are unified around our purpose: We use the power of leading-edge science to save and improve lives around the world. For more than 130 years, we have brought hope to humanity through the development of important medicines and vaccines. We aspire to be the premier research-intensive biopharmaceutical company in the world – and today, we are at the forefront of research to deliver innovative health solutions that advance the prevention and treatment of diseases in people and animals. We foster a diverse and inclusive global workforce and operate responsibly every day to enable a safe, sustainable and healthy future for all people and communities. For more information, visit www.merck.com and connect with us on X (formerly Twitter), Facebook, Instagram, YouTube and LinkedIn.

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