Anemia in men most often results from slow blood loss in the digestive tract, chronic diseases that disrupt red blood cell production, or nutritional deficiencies. While anemia is less common in men than women overall (5.5% versus 13.0%), the risk climbs sharply with age. Only about 3.9% of men aged 20 to 59 are anemic, but that number jumps to 12.8% in men 60 and older, according to national survey data from the CDC collected between 2021 and 2023.
Because men don’t lose blood through menstruation, a new diagnosis of anemia often signals an underlying problem that needs investigation. Here’s a breakdown of the most common causes.
Gastrointestinal Bleeding
Slow, hidden bleeding somewhere in the digestive tract is the single most important cause of iron deficiency anemia in men. The blood loss can be so gradual that you never notice it in your stool, but over weeks or months it drains your iron stores enough to drop your red blood cell count.
The most common culprit in the upper digestive tract is a peptic ulcer: an open sore on the stomach lining or the upper portion of the small intestine. Ulcers can bleed intermittently, making the problem easy to miss until anemia shows up on a routine blood test. Other upper GI sources include tears in the lining of the esophagus and erosion from chronic acid reflux.
In the lower digestive tract, colon polyps are a key concern. These small growths on the colon wall can bleed slowly and, in some cases, are precancerous or cancerous. Hemorrhoids and anal fissures also cause bleeding, though these tend to be more noticeable. Diverticular disease, where small pouches in the colon wall become inflamed, is another source of lower GI blood loss that becomes more common with age.
Because of this strong link, the American Gastroenterological Association recommends that men with unexplained iron deficiency anemia undergo both an upper and lower endoscopy (including colonoscopy) to rule out a serious source of bleeding. This is especially important for men over 50, where colorectal cancer becomes a more realistic possibility.
Medications That Cause Bleeding
Chronic use of nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and naproxen can irritate the stomach lining and cause slow, ongoing blood loss. Men who take these regularly for joint pain or headaches may develop anemia without any obvious symptoms of a stomach problem.
Daily low-dose aspirin deserves special attention. A large NIH-funded clinical trial found that taking just 100 mg of aspirin daily increased the risk of anemia in healthy adults 65 and older by roughly 20% over an average treatment period of 4.5 years. This effect occurred independently of any major bleeding event, meaning the aspirin caused enough low-grade blood loss to matter even when no obvious bleed was detected.
Chronic Disease and Inflammation
Long-term illnesses can cause anemia even when iron intake and blood loss are perfectly normal. This type, sometimes called anemia of chronic disease, works through a different mechanism. When your body fights persistent inflammation from conditions like rheumatoid arthritis, inflammatory bowel disease, chronic infections, or cancer, the immune system releases signaling molecules that trigger the liver to produce a hormone called hepcidin. Hepcidin essentially locks iron inside storage cells, preventing it from reaching the bone marrow where new red blood cells are made. You have iron in your body, but it’s trapped and unavailable.
The result is a slow decline in red blood cell production that doesn’t respond to iron supplements in the way a simple dietary deficiency would. Treating the underlying disease is typically what improves this type of anemia.
Kidney Disease
The kidneys produce a hormone that signals the bone marrow to make red blood cells. When kidney function declines, production of this hormone drops and the bone marrow slows down. On top of that, the buildup of waste products in the blood that comes with kidney disease shortens the lifespan of existing red blood cells, creating a double hit. Anemia is extremely common in men with moderate to advanced kidney disease and often worsens as kidney function deteriorates.
Low Testosterone
Testosterone directly stimulates the bone marrow to produce red blood cells. It does this by activating receptors inside early-stage blood cell precursors, boosting the production of new cells at the very start of the process. This is actually why men normally carry higher hemoglobin levels than women.
As men age and testosterone levels decline, this stimulating effect weakens. Research published in JAMA Internal Medicine found that low testosterone levels are independently associated with a higher risk of anemia in older men. The connection is strong enough that anemia can sometimes be an early clue pointing toward low testosterone, particularly in men over 60 who have unexplained drops in their blood counts.
Nutritional Deficiencies
Iron Deficiency
While iron deficiency in men is less often dietary than in women, it does happen. Men who eat very little red meat or follow a vegan or vegetarian diet without paying attention to iron-rich plant foods can gradually deplete their stores. However, when iron deficiency shows up in a man, the first assumption should be that iron is being lost (through bleeding) rather than simply not consumed. A dietary cause is a diagnosis of exclusion after bleeding has been ruled out.
Vitamin B12 Deficiency
B12 is essential for making healthy red blood cells. The most common cause of deficiency isn’t diet but an autoimmune condition called pernicious anemia, where the immune system attacks stomach cells that produce a protein needed to absorb B12. Without that protein, B12 from food passes straight through the digestive tract unused.
Other causes of B12 deficiency include Crohn’s disease, prior stomach surgery (such as partial gastrectomy), and certain medications. Proton pump inhibitors, commonly prescribed for acid reflux, and metformin, widely used for type 2 diabetes, both reduce B12 absorption over time. A strict vegan diet without supplementation will also lead to deficiency, since B12 is found almost exclusively in animal products.
Folate Deficiency
Folate deficiency causes a similar type of anemia to B12 deficiency, with abnormally large, poorly functioning red blood cells. It’s most common in men who eat few vegetables and legumes, or who drink heavily. Alcohol interferes with folate absorption and also damages the liver, which can increase folate loss through the kidneys. Celiac disease and other digestive conditions that impair nutrient absorption are another route to deficiency.
Inherited Blood Disorders
Some men have been anemic their entire lives due to genetic conditions that affect hemoglobin, the oxygen-carrying protein inside red blood cells.
Thalassemia is an inherited disorder where the body produces fewer functional hemoglobin proteins, causing red blood cells to have a shorter lifespan. There are two main types, alpha and beta, named after the two protein chains that make up hemoglobin. Severity depends on how many of the relevant genes are defective. A person with one faulty gene may have no symptoms at all, while someone with multiple affected genes can have moderate to severe anemia requiring ongoing treatment. Thalassemia is most common in people of Mediterranean, South Asian, Southeast Asian, and Middle Eastern descent.
Sickle cell disease, most common in people of African, Middle Eastern, and South Asian ancestry, causes red blood cells to become rigid and crescent-shaped, leading to chronic anemia alongside episodes of pain and other complications. Men with sickle cell trait (one copy of the gene) usually don’t develop significant anemia, but those with two copies have the full disease.
Why the Cause Matters More in Men
In premenopausal women, anemia has an obvious and common explanation: menstrual blood loss. In men, there is no equivalent routine source of blood loss, so anemia almost always points to something else going on. This is why doctors take anemia in men seriously as a diagnostic finding rather than treating it as a standalone problem. Iron deficiency anemia in a man over 50, for example, warrants a colonoscopy not because the anemia itself is dangerous, but because it could be the first sign of colon cancer or another treatable GI condition. The anemia is the clue, and following it to the underlying cause is what matters most.