Nutrition Diet: What is the number one cause of iron deficiency anemia?

October 8, 2025 •

4 min read

According to the World Health Organization, iron deficiency is the single most common nutritional deficiency worldwide, affecting over 2 billion people globally. It is a frequent precursor to anemia, and understanding what is the number one cause of iron deficiency anemia is crucial for effective prevention and treatment.

Quick Summary

Blood loss is the most common cause of iron deficiency anemia, with heavy menstrual bleeding affecting premenopausal women and gastrointestinal bleeding impacting men and postmenopausal women. The root cause must be addressed for effective treatment beyond just diet.

Key Points

Blood Loss is the Primary Cause: For many adults, chronic blood loss from sources like heavy periods or GI bleeding is the number one cause, not just inadequate dietary intake.
Demographics Matter: In premenopausal women, heavy menstruation is the most common cause, while in men and postmenopausal women, gastrointestinal bleeding is the primary concern.
Dietary Role and Absorption: While diet contributes, absorption is critical. The body absorbs more easily from heme iron (animal sources) than non-heme iron (plant sources).
Medical Investigation is Necessary: Finding the underlying cause of chronic bleeding is essential, especially in cases of suspected gastrointestinal issues in men and postmenopausal women.
Vitamin C Boosts Absorption: To maximize absorption of non-heme iron from plant sources, consume it with foods rich in Vitamin C, like citrus fruits or broccoli.

The underlying reason for iron deficiency anemia is not a one-size-fits-all answer. While nutritional intake plays a vital role, the primary culprit often varies by demographics and underlying health conditions. For many, especially adults in developed countries, the most significant factor is chronic blood loss rather than simply not eating enough iron-rich foods.

The Role of Chronic Blood Loss

In the grand scheme, chronic blood loss is the number one driver of iron deficiency anemia, surpassing other factors like poor diet in many adult populations. Iron is a core component of hemoglobin in red blood cells. When blood is lost, iron is lost along with it. If this loss is persistent and not compensated for by increased iron intake or absorption, the body's iron stores become depleted, leading to anemia.

Heavy Menstrual Bleeding

For premenopausal women, heavy menstrual bleeding is the single most common cause of iron deficiency anemia. The amount of iron lost during a menstrual period can be substantial, with women needing to absorb more iron than men just to maintain equilibrium. When blood loss exceeds the body's ability to absorb iron from diet, stores dwindle, often going unnoticed until symptoms of anemia appear. Many women do not realize their menstrual flow is heavy enough to cause an issue, and they may write off symptoms like fatigue as normal.

Gastrointestinal (GI) Bleeding

In men and postmenopausal women, the most frequent cause of iron deficiency is chronic blood loss from the gastrointestinal tract. This bleeding can be slow and occult, meaning it is not visible to the naked eye. Common sources include:

Bleeding ulcers or polyps
Inflammatory bowel diseases like Crohn's disease or ulcerative colitis
Gastrointestinal cancers, particularly in older adults
Regular use of certain medications, such as aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs)

Because the blood loss is often not apparent, it is critical for healthcare providers to investigate the GI tract when anemia is discovered in these populations.

Dietary Insufficiency and Absorption Issues

While blood loss takes the top spot for many adults, nutritional factors are still significant contributors, especially globally and in specific groups.

Inadequate Dietary Iron Intake

Inadequate iron intake can contribute to or cause iron deficiency, particularly in regions where meat consumption is low. For populations in developed countries, poor diet is more common among specific groups, such as vegetarians, vegans, and those with restricted diets. The body absorbs two types of iron from food: heme iron, found in animal products, which is more easily absorbed, and non-heme iron, found in plant-based foods, which is less efficiently absorbed.

Malabsorption

Even with adequate dietary intake, some individuals struggle to absorb iron effectively. Conditions that cause malabsorption include:

Celiac disease: An autoimmune disorder that damages the lining of the small intestine.
Inflammatory bowel disease: Chronic inflammation can impair nutrient absorption.
Bariatric surgery: Procedures that bypass or remove part of the stomach or small intestine reduce the area where iron is absorbed.
Low stomach acid: Chronic conditions or medications like proton-pump inhibitors can reduce the acidity needed to convert iron into its absorbable form.

Increased Iron Requirements

Some life stages naturally increase the body's demand for iron, making deficiency more likely if dietary needs aren't met:

Pregnancy: A pregnant person's blood volume increases significantly, and iron is needed for the growing fetus and placenta.
Infants and children: Periods of rapid growth require a higher iron intake.
Athletes: Intense exercise can increase red blood cell production and cause iron loss through sweat.

Diagnosis and Treatment of Iron Deficiency Anemia

Diagnosing iron deficiency anemia requires a blood test, which typically includes a complete blood count (CBC) to check hemoglobin and hematocrit levels, as well as serum ferritin levels to assess iron stores. Treatment focuses on correcting the underlying cause and replenishing iron stores.

Treatment Options

Oral Iron Supplements: A common treatment involves taking iron tablets for several months to rebuild iron stores. Taking supplements with vitamin C-rich foods can enhance absorption.
Intravenous (IV) Iron: For individuals who cannot tolerate oral supplements, have malabsorption issues, or require a rapid increase in iron levels, IV iron infusions are an option.
Addressing the Cause: Treating the source of bleeding, such as a peptic ulcer or heavy periods, is a critical step to prevent recurrence.

Heme vs. Non-Heme Iron Sources

To effectively manage iron levels through diet, it's important to understand the difference between heme and non-heme iron and their absorption rates. A comparative table highlights key differences.


Feature	Heme Iron	Non-Heme Iron
Source	Animal products (meat, poultry, seafood)	Plant-based foods (vegetables, grains, legumes, nuts)
Absorption Rate	Higher and more consistent	Lower and more dependent on dietary factors
Absorption Enhancers	Not significantly affected by enhancers	Enhanced by Vitamin C and animal protein
Absorption Inhibitors	Minimally affected	Inhibited by tannins (tea, coffee), phytates (grains), and calcium

Conclusion

While a poor diet can contribute, the single biggest cause of iron deficiency anemia in many adult populations is chronic blood loss. The specific source of that bleeding, however, differs significantly between populations, with heavy menstruation most common in premenopausal women and gastrointestinal issues topping the list for men and postmenopausal women. For effective management, it is crucial to both address the root cause and optimize iron intake through diet and supplementation. Understanding these distinct causes and tailored management strategies is key to a healthier nutritional status.

For more in-depth medical information on iron deficiency, consult reliable resources like the National Institutes of Health.

Frequently Asked Questions

The most common cause is chronic blood loss. For premenopausal women, this is typically due to heavy menstrual bleeding. For men and postmenopausal women, it often results from gastrointestinal bleeding.

Yes, an inadequate dietary intake of iron is a significant factor, especially in certain populations like vegans, vegetarians, and young children. However, chronic blood loss is often the dominant cause in adults.

Common symptoms include fatigue, weakness, pale skin, shortness of breath, dizziness, cold hands and feet, headaches, a fast heartbeat, and brittle nails. Some people also experience cravings for non-food items like ice or clay.

Diagnosis is confirmed with blood tests. A doctor will typically order a complete blood count (CBC) to check hemoglobin levels, and a ferritin test to measure the body's iron stores.

To increase absorption of non-heme iron from plant-based foods, pair them with foods high in vitamin C, such as citrus fruits, tomatoes, and bell peppers. Avoid drinking coffee or tea with iron-rich meals, as they can inhibit absorption.

Good sources of iron include lean red meat (heme iron, highly absorbable), poultry, fish, beans, lentils, peas, tofu, dark leafy green vegetables, and iron-fortified cereals and bread (non-heme iron).

No, it is not recommended to self-treat. While supplements are often necessary, a healthcare provider should first determine the underlying cause and recommend the appropriate approach. Excessive iron intake can be harmful.