In men, low iron is almost always caused by blood loss somewhere in the body or by a condition that blocks iron absorption. Unlike women, men don’t lose iron through menstruation, so when iron levels drop, it typically signals an underlying problem worth investigating. The recommended daily iron intake for adult men is just 8 mg, half of what premenopausal women need, which means the male body is designed to hold onto iron efficiently. When it can’t, something is interfering.
GI Bleeding Is the Most Common Cause
The leading reason men develop iron deficiency is slow, chronic bleeding in the gastrointestinal tract. This kind of bleeding often happens in small amounts over weeks or months, so you may never notice blood in your stool. A peptic ulcer, hiatal hernia, colon polyp, or colorectal cancer can all cause this type of hidden blood loss. Inflammatory bowel conditions like Crohn’s disease and ulcerative colitis are also common culprits, both because they cause intestinal bleeding and because the inflammation itself interferes with how your body handles iron.
What makes GI bleeding particularly important to take seriously is its link to colorectal cancer. A study published in the journal Gut found that men with iron deficiency anemia had a five-year colorectal cancer incidence of 0.85%, roughly ten times higher than men without iron deficiency. That’s still a small absolute number, but it’s why doctors treat unexplained low iron in men as a red flag that warrants a colonoscopy or endoscopy, especially in men over 40.
Regular use of nonsteroidal anti-inflammatory drugs (like ibuprofen or aspirin) can also erode the stomach lining enough to cause slow bleeding. If you take these medications daily for joint pain or heart health, they may be quietly draining your iron stores.
Poor Absorption Can Be Just as Significant
Even if you’re eating plenty of iron-rich food, certain conditions prevent your gut from absorbing it properly. Celiac disease is one of the most common absorption problems. When someone with celiac disease eats gluten, it damages the lining of the small intestine, particularly the upper section where most iron absorption happens. Some men are diagnosed with celiac disease only after their doctor investigates unexplained iron deficiency.
Gastric bypass and other weight-loss surgeries also reduce iron absorption by rerouting food past the parts of the intestine that take up iron most efficiently. If you’ve had bariatric surgery, iron deficiency can develop months or even years later as your body’s stored reserves gradually deplete.
Chronic Kidney Disease and Inflammation
Chronic kidney disease (CKD) creates a double hit on iron levels. Damaged kidneys produce less of the hormone that stimulates red blood cell production, and at the same time, the ongoing inflammation that accompanies CKD triggers the liver to release a regulatory protein called hepcidin. Elevated hepcidin blocks iron absorption in the gut and traps existing iron inside storage cells so it can’t be used to make new red blood cells. The result is a form of iron deficiency where your body may technically have some iron in reserve but can’t access it.
This same mechanism applies to other chronic inflammatory conditions, including rheumatoid arthritis, heart failure, and chronic infections. The inflammation itself disrupts iron metabolism, which is why treating the underlying condition often matters more than simply taking iron supplements.
Diet Rarely Works Alone, but It Matters
Pure dietary iron deficiency is uncommon in men living in developed countries, since most diets provide enough to meet the 8 mg daily requirement. But certain dietary patterns can push you toward deficiency if another risk factor is already in play. Vegetarian and vegan diets provide only non-heme iron (the plant-based form), which the body absorbs at roughly 2 to 5 percent efficiency compared to 15 to 35 percent for the heme iron found in meat, poultry, and fish.
Heavy tea or coffee consumption with meals can also reduce absorption, since the tannins and polyphenols in these drinks bind to iron in the gut. On the flip side, vitamin C significantly boosts non-heme iron absorption, so pairing iron-rich foods with citrus, bell peppers, or tomatoes makes a measurable difference.
Endurance Exercise and Iron Loss
Male endurance athletes, particularly runners, face a less obvious route to low iron. Each time your foot hits the ground during a run, the impact mechanically destroys red blood cells passing through the capillaries in your feet. Research published in the Journal of Applied Physiology confirmed this by comparing runners to cyclists: the increase in markers of red blood cell destruction was four times greater after running than after cycling, where there’s no repetitive foot impact. Even shoe choice plays a role. Runners training in hard-soled shoes showed 29 percent more immature red blood cells (a sign the body is working harder to replace destroyed ones) compared to those in cushioned shoes.
On top of this mechanical destruction, endurance athletes lose small amounts of iron through sweat and, in some cases, through microscopic GI bleeding triggered by reduced blood flow to the gut during prolonged exercise. If you’re running 40 or more miles per week and feeling unusually fatigued, iron deficiency is worth checking.
How Low Iron Is Detected
The standard screening test measures ferritin, a protein that reflects your body’s iron stores. For men, the normal ferritin range is 24 to 336 micrograms per liter. Results below 24 indicate iron deficiency, though symptoms like fatigue, weakness, and difficulty concentrating can start appearing before levels drop that low, particularly if iron stores have been declining steadily.
A complete blood count often shows the downstream effects: smaller-than-normal red blood cells, lower hemoglobin, and reduced oxygen-carrying capacity. But ferritin is the earlier and more specific marker. One important caveat is that ferritin rises during inflammation and infection, so a “normal” ferritin reading in someone with a chronic inflammatory condition can mask true iron deficiency. In those cases, additional tests that measure how much iron is actively available in the blood give a clearer picture.
What Happens After Diagnosis
Because low iron in men almost always points to an underlying cause, the diagnostic workup typically goes beyond blood tests. Most men will be referred for an upper endoscopy, a colonoscopy, or both, to look for sources of GI bleeding. Celiac screening through a blood antibody test is also standard. If kidney disease or another chronic condition is suspected, additional lab work follows.
Iron replacement itself usually starts with oral supplements taken on an empty stomach, though these commonly cause constipation and nausea. Taking supplements every other day rather than daily has been shown to improve absorption rates while reducing side effects. For men with absorption problems or severe deficiency, intravenous iron delivers the mineral directly into the bloodstream and can replenish stores within a few weeks rather than the three to six months oral supplements typically require. But regardless of how iron is replaced, finding and addressing the reason it dropped in the first place is the more important step.