What Causes Iron to be Low? An Exploration of Root Causes

January 6, 2026 •

3 min read

According to the World Health Organization, iron deficiency is the most common nutritional disorder worldwide, and understanding what causes iron to be low is the first step toward effective treatment. Often stemming from a complex interplay of dietary habits, physiological changes, and underlying health issues, low iron is more than just a matter of insufficient intake.

Quick Summary

Low iron results primarily from blood loss, inadequate dietary intake, poor absorption, or increased bodily demands. Contributing factors include heavy menstrual bleeding, gastrointestinal issues, vegetarian diets, and conditions like celiac disease or pregnancy.

Key Points

Blood Loss is Common: In adults, especially premenopausal women, blood loss from heavy periods or internal bleeding is a primary reason for low iron.
Dietary Intake Matters: Vegetarians and vegans, as well as those with restrictive diets, are at higher risk due to lower bioavailability of non-heme iron.
Absorption Issues Play a Role: Digestive conditions like celiac disease or inflammatory bowel disease can prevent the body from effectively absorbing iron, regardless of dietary intake.
Life Stages Increase Demand: Pregnancy, infancy, and adolescent growth spurts significantly increase the body's iron requirements, potentially leading to deficiency if not supplemented.
Inflammation Can Block Iron Use: Chronic inflammatory conditions trigger the release of hepcidin, a hormone that traps iron in the body's storage cells, making it inaccessible for red blood cell production.
Medications Affect Levels: Stomach acid-reducing medications, such as PPIs, can negatively impact iron absorption in the small intestine.
Treatment Depends on the Cause: Simply taking iron supplements may not resolve the issue if the underlying cause, like chronic bleeding, is not addressed by a healthcare provider.

The Primary Causes of Low Iron

Iron is a vital mineral required for the production of hemoglobin, the protein in red blood cells that carries oxygen throughout the body. A shortage of iron depletes the body's iron stores and can eventually lead to iron-deficiency anemia. The depletion of these stores typically arises from four main causes: blood loss, insufficient intake, poor absorption, and increased demand.

Blood Loss

Blood loss is the most common cause of low iron in adults, as hemoglobin within red blood cells contains significant amounts of iron. Chronic, slow bleeding can deplete the body's iron reserves over time, often without obvious symptoms. Common sources include heavy menstrual bleeding, gastrointestinal bleeding from conditions like ulcers or polyps, and frequent blood donation. Less common causes include bleeding from the urinary tract or recurrent nosebleeds.

Insufficient Dietary Iron Intake

While the American diet is often fortified with iron, inadequate intake remains a key factor, especially in certain populations. The body cannot produce its own iron, so it must be obtained from food. Vegetarian and vegan diets are at higher risk as plant-based non-heme iron is less readily absorbed than the heme iron from meat. Infants who don't get enough iron from breast milk or fortified formula, or children who consume excessive cow's milk, can also develop low iron.

Impaired Iron Absorption

Sometimes, a person's diet is rich in iron, but their body cannot effectively absorb it. Iron is absorbed in the small intestine, and certain conditions can interfere with this process. Conditions like celiac disease and inflammatory bowel disease damage the small intestine lining, hindering nutrient absorption. Digestive surgeries, such as gastric bypass, can also limit the area for iron absorption. Certain medications, like proton pump inhibitors, reduce stomach acid needed for iron absorption.

Increased Iron Demand

During certain life stages, the body's need for iron increases significantly. This includes pregnancy, where iron is needed for increased blood volume and the developing fetus, and periods of rapid growth in infants and adolescents. Endurance athletes may also have increased iron requirements due to red blood cell breakdown during high-impact activity.

Other Contributing Factors and Complications

Chronic Inflammation

Chronic inflammation from conditions like autoimmune diseases or chronic kidney disease can lead to 'anemia of chronic disease'. Inflammation increases hepcidin, a hormone that blocks iron release from storage and reduces intestinal absorption, trapping iron in storage.

Impact on Overall Health

Low iron can cause fatigue, weakness, pale skin, cold hands and feet, and in severe cases, a fast heartbeat or shortness of breath. It can also weaken the immune system, impair cognition, and cause restless leg syndrome. Addressing the underlying cause is essential for treatment and preventing complications.

Comparison of Major Causes of Low Iron


Cause	Key Mechanism	Common Examples	At-Risk Populations
Blood Loss	Loss of iron-rich red blood cells	Heavy menstruation, GI bleeding (ulcers, polyps)	Premenopausal women, men & postmenopausal women with occult GI issues
Poor Absorption	Inability to absorb iron from the small intestine	Celiac disease, gastric bypass surgery, H. pylori infection	People with GI disorders or post-surgery patients
Increased Demand	Body requires more iron than can be consumed	Pregnancy, rapid growth periods in children and adolescents	Pregnant individuals, infants, toddlers, teenagers
Insufficient Intake	Diet does not provide enough iron	Lack of iron-rich foods, particularly non-heme iron sources	Vegetarians, vegans, and individuals with low caloric intake
Chronic Inflammation	Hepcidin production traps iron in storage	Chronic kidney disease, autoimmune diseases, obesity	People with chronic inflammatory conditions

Conclusion

Identifying the underlying cause of low iron is crucial for effective treatment, as factors beyond diet, such as blood loss, absorption issues, increased demand, and chronic inflammation, are often involved. For more detailed information on iron deficiency and anemia, refer to reliable medical sources like the {Link: National Heart, Lung, and Blood Institute https://www.nhlbi.nih.gov/health/anemia/iron-deficiency-anemia}.

Frequently Asked Questions

Symptoms of low iron can be subtle at first and include fatigue, weakness, pale skin, and cold hands and feet. As it worsens, people may experience a fast heartbeat, shortness of breath, or dizziness.

For most people with a true iron deficiency, diet alone is not enough to restore iron stores, and oral or intravenous supplementation is often necessary. However, a diet rich in iron can help prevent future issues once the underlying cause is addressed.

No, iron deficiency is not the same as iron-deficiency anemia, but it is a precursor. Iron deficiency can exist without anemia, meaning iron stores are low but hemoglobin is still within a normal range. When iron stores and hemoglobin levels drop, it progresses to anemia.

Yes, a doctor should diagnose and investigate the cause of low iron. The condition is diagnosed through blood tests, and finding the root cause is crucial, as it could be a sign of a more serious underlying condition like internal bleeding.

Iron-rich foods include meat, poultry, and fish (heme iron, highly absorbable), and fortified cereals, leafy green vegetables, and beans (non-heme iron). Consuming vitamin C with plant-based iron can boost absorption.

Proton pump inhibitors and other antacids reduce stomach acid, which is necessary to convert dietary iron into a form your body can absorb in the small intestine. Long-term use can therefore impair iron absorption and lead to deficiency.

Yes, frequent blood donation can lead to low iron levels. With every donation, a significant amount of iron is lost, and regular donors need to ensure they have an adequate intake to replenish their stores.