What Causes You to Lose Iron in Your Body?

December 30, 2025 •

4 min read

Iron deficiency is the most common nutritional deficiency worldwide, affecting over 1.6 billion people. While diet is often the first suspect, inadequate intake is only one piece of the puzzle. Losing iron can happen for a number of reasons, with blood loss being a primary culprit in many cases.

Quick Summary

Chronic blood loss, particularly from heavy menstruation or the gastrointestinal tract, is a leading cause of iron deficiency. Poor iron absorption due to digestive disorders or surgery also contributes, as do increased bodily demands during pregnancy and growth.

Key Points

Chronic Blood Loss: Heavy menstruation in women and gastrointestinal bleeding in men and postmenopausal women are the leading causes of iron loss.
Impaired Absorption: Digestive conditions like celiac disease and Crohn's disease can prevent the body from properly absorbing iron from food.
Increased Physiological Needs: Pregnant women and growing children require significantly more iron, which can lead to deficiency if intake is insufficient.
Dietary Factors: A diet low in iron or high in iron-inhibiting substances like phytates and tannins can cause iron depletion over time.
Intense Exercise: Endurance athletes lose iron through sweat and gastrointestinal blood loss, increasing their risk of deficiency.
Medication Side Effects: Regular use of certain medications, such as NSAIDs, can cause internal bleeding that leads to iron loss.
Post-Surgical Malabsorption: Surgical procedures like gastric bypass can reduce the body's ability to absorb nutrients, including iron.

Blood Loss: The Primary Reason for Iron Depletion

Chronic and significant blood loss is a leading cause of iron deficiency, especially in adults. When you lose blood, you also lose the iron contained within your red blood cells, which the body must then replace. If this blood loss is ongoing and not addressed, it can lead to depleted iron stores and, eventually, iron deficiency anemia. The sources of this blood loss can vary, often going unnoticed for extended periods.

Menstrual Blood Loss

For women of childbearing age, heavy menstrual bleeding (menorrhagia) is the most common cause of iron deficiency. An average woman loses approximately 1 mg of iron per menstrual cycle, but those with heavy periods can lose five to six times more. If dietary intake cannot keep up with this loss, iron stores are gradually depleted over time, leading to fatigue and other symptoms. Medical conditions like uterine fibroids or endometriosis can further exacerbate menstrual bleeding and iron loss.

Gastrointestinal Bleeding

In men and postmenopausal women, iron deficiency often points to blood loss in the digestive tract. This bleeding may be slow and not immediately visible, a condition known as occult blood loss. A wide range of gastrointestinal (GI) issues can be responsible, including:

Peptic ulcers: Sores in the lining of the stomach or small intestine can bleed over time.
Inflammatory bowel disease (IBD): Conditions like Crohn's disease or ulcerative colitis cause chronic inflammation and ulceration, leading to blood loss from the bowel.
Celiac disease: Damage to the small intestine lining can cause chronic bleeding.
Medication use: Regular use of nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin or ibuprofen can irritate the stomach lining and cause bleeding.
GI cancers: Tumors in the stomach or colon can be a cause of blood loss, making investigation crucial in some cases.

Other Sources of Blood Loss

Beyond menstruation and GI issues, other factors can lead to blood loss and subsequent iron deficiency:

Frequent blood donation: Regular blood donors are at a higher risk of depleting their iron stores.
Urinary tract bleeding: Blood loss can sometimes occur in the urine due to certain medical conditions.
Trauma or surgery: Acute blood loss from injuries or surgical procedures can cause iron levels to drop quickly.

Impaired Iron Absorption

Even with adequate dietary iron intake, some individuals lose iron due to impaired absorption. This happens when the body cannot effectively absorb the iron from food through the digestive tract.

Medical Conditions Affecting Absorption

Several chronic medical conditions can interfere with the body's ability to absorb iron:

Celiac disease: As mentioned, this autoimmune condition damages the small intestine lining where iron is absorbed.
Crohn's disease: Chronic inflammation can hinder the absorption process.
Helicobacter pylori infection: This bacterial infection can cause gastritis and reduced stomach acid, both of which impair iron absorption.
Gastric bypass surgery: Procedures that bypass sections of the small intestine can significantly reduce iron absorption.

Dietary Inhibitors

Certain foods and compounds can also reduce iron absorption, especially non-heme iron from plant sources. These inhibitors include:

Phytates: Found in whole grains, cereals, and legumes.
Calcium: High amounts of calcium can interfere with iron uptake.
Polyphenols: Present in coffee and tea, which should be consumed a couple of hours away from iron-rich meals.

Increased Demand for Iron

In some life stages, the body's need for iron increases significantly, and if not met, can lead to a state of iron deficiency.

Pregnancy and Growth

Pregnant women require a much higher intake of iron to support the increased blood volume and the needs of the developing fetus. Similarly, infants and young children going through rapid growth spurts need more iron to build new blood cells and tissues.

Athletes

Endurance athletes are prone to iron deficiency due to a combination of factors. They have an increased need for iron to produce more red blood cells for oxygen transport. Furthermore, iron can be lost through sweat, the gastrointestinal tract during strenuous exercise, and a process called 'foot strike hemolysis,' where red blood cells are damaged by the impact of running.

Comparison of Major Iron Loss Causes


Factor	Primary Mechanism	Impact on Iron Levels	Who is Most at Risk?
Heavy Menstruation	Chronic external blood loss	Direct and significant loss with each cycle	Premenopausal women, especially with fibroids or endometriosis.
Gastrointestinal Bleeding	Chronic internal blood loss	Slow, often undetectable depletion over time	Men and postmenopausal women.
Malabsorption	Impaired intestinal uptake	Prevents absorption of dietary iron	Individuals with celiac disease, IBD, or post-bariatric surgery.
Increased Demand (Pregnancy)	Higher requirements for fetus	Depletes maternal iron stores rapidly if not supplemented	Pregnant women.
Intense Athletic Training	Increased need + losses via sweat/GI tract	Gradual depletion due to higher turnover and losses	Endurance athletes, especially female athletes.

Conclusion

Losing iron can be attributed to several factors, with chronic blood loss from heavy periods or the GI tract being the most common causes. Impaired absorption due to digestive disorders and increased bodily demand during pregnancy and intense exercise are also significant contributors. Recognizing these root causes is essential for diagnosis and effective treatment, which may involve dietary adjustments, supplementation, or addressing underlying medical conditions. If you suspect an iron deficiency, it is vital to consult a healthcare professional to identify the exact cause and determine the best course of action. For more information, visit the National Institutes of Health (NIH) website.

Note: Do not self-diagnose or start supplementation without consulting a healthcare provider.

Frequently Asked Questions

Yes, heavy menstrual bleeding (menorrhagia) is one of the most common causes of iron deficiency in women of reproductive age. The body loses iron along with blood, and if intake doesn't keep up with the monthly loss, iron stores can become depleted over time.

Internal bleeding that leads to iron loss is often chronic and slow, occurring in the gastrointestinal tract due to conditions like peptic ulcers, inflammatory bowel disease, or certain cancers. It can also be a side effect of some medications like NSAIDs.

Vegetarians and vegans can be at a higher risk of iron deficiency because non-heme iron, found in plants, is not as easily absorbed as heme iron, found in meat. It is important for those on plant-based diets to be mindful of their iron intake and eat foods that enhance absorption.

Endurance athletes are susceptible to iron deficiency due to several factors, including increased need for red blood cell production, iron loss through sweat, and minor blood loss from the digestive tract during strenuous training.

Yes, gastric surgeries, such as gastric bypass, can lead to iron deficiency by bypassing parts of the small intestine where iron is absorbed, reducing the body's ability to take in the mineral.

During pregnancy, the body's iron requirements increase significantly to support the mother and the developing fetus. Many pregnant individuals develop iron deficiency and require iron supplements to maintain healthy levels.

Certain substances can inhibit iron absorption. These include phytates found in whole grains, high amounts of calcium, and polyphenols found in coffee and tea. It is recommended to separate the intake of these items from iron-rich meals.