The Main Cause of Iron Deficiency Explained

January 10, 2026 •

4 min read

According to the World Health Organization, iron deficiency is the most common nutritional disorder worldwide. While inadequate dietary intake is a factor, the main cause of iron deficiency in adults is often chronic blood loss, which can be overlooked and requires medical investigation.

Quick Summary

Chronic blood loss is the primary driver of iron deficiency in adults, though poor diet, malabsorption, and increased bodily demands also contribute. Identifying the underlying cause is crucial for effective treatment.

Key Points

Blood Loss is a Primary Driver: For many adults, particularly men and postmenopausal women, chronic or occult (hidden) blood loss, often from the gastrointestinal tract, is the primary cause of iron deficiency.
Menstrual Bleeding Affects Women: Heavy or prolonged menstrual periods are the most common cause of iron deficiency in premenopausal women.
Dietary Intake is a Contributor, Not Always the Main Factor: While low iron intake can cause deficiency, especially in vegans, it's not the main cause for many adults in developed countries due to fortified foods.
Malabsorption Can Be the Root Issue: Conditions like celiac disease or gastrointestinal surgeries can impair the body's ability to absorb iron, regardless of dietary intake.
Increased Needs Play a Role: Pregnancy and rapid growth in children significantly increase iron requirements, making these groups more susceptible to deficiency.
Medical Investigation is Essential: Because the root cause can be a serious underlying condition like a bleeding ulcer, medical diagnosis is crucial for effective and lasting treatment.

Why Is Iron So Important?

Iron is a vital mineral that plays a crucial role in producing hemoglobin, the protein in red blood cells that carries oxygen from the lungs to the rest of the body. A deficit of iron can lead to iron-deficiency anemia, causing symptoms like fatigue, shortness of breath, and pale skin. To effectively treat the condition, one must understand and address the main cause of iron deficiency.

The Overarching Cause: Blood Loss

For adults, particularly in developed countries, blood loss is the most common and significant cause of iron deficiency. Unlike other nutrient deficiencies, where low dietary intake is the primary driver, iron deficiency often signals an issue where iron is being lost from the body faster than it can be replaced. This is especially true for men and postmenopausal women, where gastrointestinal bleeding is a prime suspect and requires serious investigation.

Common Sources of Blood Loss

Menstrual Bleeding: Heavy or prolonged menstrual periods are the most frequent cause of iron deficiency in premenopausal women.
Gastrointestinal Bleeding: This can result from various conditions and may not be visible in stool, requiring medical testing to identify. Potential causes include peptic ulcers, colon polyps, inflammatory bowel disease, or, in less common cases, gastrointestinal cancers.
Frequent Blood Donation: Regular blood donors lose iron with each donation and may be at a higher risk of deficiency.
Medication Use: Long-term use of certain nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin and ibuprofen can cause gastrointestinal bleeding.

Contributing Factors Beyond Blood Loss

While blood loss is often the primary cause, several other factors can deplete the body's iron stores and are particularly relevant in specific populations.

Dietary Insufficiency

Though less common in countries with iron-fortified foods, inadequate dietary intake can be a major factor for some groups, including:

Strict Vegetarians and Vegans: Iron from plant-based sources (non-heme iron) is not as readily absorbed by the body as iron from meat (heme iron).
Infants and Young Children: During periods of rapid growth, infants and children require more iron. Picky eating or diets with a high intake of cow's milk can increase their risk.
Specialized Diets: An unbalanced or restrictive diet that fails to include enough iron-rich foods, especially during growth spurts, can lead to deficiency.

Impaired Iron Absorption

Sometimes, even with sufficient dietary iron, the body cannot absorb it effectively. This condition, known as malabsorption, can stem from several health issues:

Celiac Disease: This autoimmune disorder damages the lining of the small intestine, impairing nutrient absorption.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can reduce iron absorption.
Gastric Bypass Surgery: Surgical alterations to the digestive tract can reduce the body's ability to absorb iron.

Increased Iron Requirements

Certain life stages and medical conditions increase the body's demand for iron, making deficiency more likely:

Pregnancy: The body's blood volume increases, and the growing fetus requires iron, significantly raising the mother's iron needs.
Growth Spurts: Children and adolescents experience rapid growth, requiring more iron to produce new red blood cells.
Dialysis: Patients with kidney failure on dialysis are often at risk for iron deficiency and are routinely monitored.

Comparison: Primary Causes of Iron Deficiency

To better understand the likelihood of different causes, the following table compares the typical primary causes for various demographics.


Demographic	Most Common Primary Cause	Other Contributing Factors	Diagnostic Considerations
Premenopausal Women	Heavy menstrual bleeding	Pregnancy, dietary intake	Assess menstrual cycle, pregnancy status, and diet.
Men & Postmenopausal Women	Gastrointestinal (GI) blood loss	Chronic NSAID use, malabsorption	Investigate occult GI bleeding through endoscopy.
Infants & Young Children	Inadequate dietary intake	Rapid growth, excessive cow's milk	Evaluate dietary habits and potential malabsorption issues.
Vegetarians & Vegans	Low dietary intake (poor absorption)	Strict dietary habits, growth spurts	Focus on dietary sources and supplementation needs.
Post-Gastric Surgery Patients	Impaired iron absorption	Lower dietary intake	Closely monitor and manage supplementation post-surgery.
Patients on Dialysis	Increased iron requirements & loss	Chronic kidney disease	Regular monitoring is essential due to high risk.

Conclusion

While a poor diet is a familiar culprit, the main cause of iron deficiency in adults, particularly men and postmenopausal women, is often chronic blood loss. For premenopausal women, heavy menstruation is a primary factor. Conditions that impair absorption, like celiac disease, also play a significant role. Regardless of the specific cause, a diagnosis requires a healthcare professional to identify the root issue, as simply supplementing with iron may not be enough to prevent recurrence. A thorough medical evaluation is key to identifying and treating the underlying problem, leading to better long-term health outcomes. Seeking medical advice is the most important step for anyone with suspected iron deficiency.

Visit Cleveland Clinic for more detailed information on iron deficiency anemia.

Frequently Asked Questions

Heavy menstrual bleeding is the most common cause of iron deficiency in premenopausal women, where significant blood loss can deplete the body's iron stores over time.

Yes, a poor diet can contribute to iron deficiency, especially in individuals like strict vegetarians who do not consume enough readily-absorbed iron from meat. However, in many cases, especially for adults, a more significant underlying issue like blood loss is the main cause.

Blood contains iron, and when adults lose blood, they lose a significant amount of iron. Since the body reuses iron from red blood cells, chronic loss depletes these reserves faster than they can be replenished through diet alone.

Less obvious sources of blood loss include internal gastrointestinal bleeding from conditions like ulcers, polyps, or certain cancers, and chronic use of NSAIDs like aspirin or ibuprofen.

Intestinal conditions such as celiac disease, Crohn's disease, or gastric bypass surgery can all interfere with the body's ability to absorb iron from food in the small intestine, leading to a deficiency regardless of dietary intake.

During pregnancy, a woman's blood volume increases significantly, and iron is required for the development of both the mother and the fetus. This increased demand can easily lead to iron deficiency if not managed with proper diet or supplementation.

Iron supplements can treat the deficiency temporarily, but they do not address the root cause. To ensure the problem doesn't return, a medical professional must diagnose and treat the underlying issue, whether it's blood loss, malabsorption, or another factor.