What is the most common cause of low Hgb?

September 22, 2025 •

3 min read

Iron deficiency is the most common cause of anemia worldwide, a condition directly linked to low hemoglobin (Hgb). Your body needs iron to produce Hgb, the protein in red blood cells that carries oxygen throughout the body.

Quick Summary

The most common cause of low hemoglobin is iron deficiency, a condition where the body lacks sufficient iron to produce adequate hemoglobin for oxygen transport. It can result from dietary insufficiency, poor absorption, or blood loss from sources like heavy menstrual bleeding or internal bleeding from conditions such as ulcers.

Key Points

Iron Deficiency: The most common cause of low Hgb is iron deficiency, leading to a condition called iron-deficiency anemia.
Causes of Iron Deficiency: Main causes include blood loss (e.g., heavy periods or GI bleeding), inadequate dietary iron intake, poor absorption due to intestinal issues, and increased bodily demands during pregnancy.
Other Anemia Types: Low Hgb can also be caused by other nutritional deficiencies (like B12 or folate), chronic diseases (e.g., kidney disease), or issues with bone marrow production.
Diagnosis: A complete blood count (CBC) is the standard test to check Hgb levels. Further testing is needed to determine the specific cause.
Treatment: Treatment depends on the cause and may involve iron supplements, addressing blood loss, correcting other nutritional deficiencies, or managing an underlying chronic condition.
Dietary Role: Increasing dietary intake of iron-rich foods, particularly from animal sources, and consuming vitamin C to enhance absorption is a common strategy.

Understanding Hemoglobin and Anemia

Hemoglobin (Hgb) is a protein in red blood cells that transports oxygen. Low Hgb leads to anemia, where tissues don't get enough oxygen.

Iron Deficiency: The Leading Culprit

Iron deficiency is the most common global cause of low Hgb, resulting in iron-deficiency anemia. Without enough iron, the body can't produce sufficient Hgb. This is common in pregnant individuals, women with heavy periods, and those with certain gut conditions.

Causes of Iron Deficiency

Several factors can lead to low iron:

Diet: Not eating enough iron-rich foods is a key cause, especially for infants, children, vegans, and vegetarians.
Blood Loss: Losing blood means losing iron. Causes include heavy periods, chronic bleeding from ulcers or polyps, and frequent blood donation.
Malabsorption: Conditions like celiac disease or gastric bypass surgery can hinder iron absorption.
Increased Demand: Growth spurts and pregnancy increase the need for iron.

Other Potential Causes of Low Hemoglobin

Beyond iron deficiency, other issues can lower Hgb:

Nutritional Deficiencies

Lack of Vitamin B12 or folate can cause megaloblastic anemia.

Bone Marrow Problems

Aplastic anemia or diseases like leukemia can impair blood cell production.

Red Blood Cell Destruction

Hemolytic anemias occur when red blood cells are destroyed too quickly. This can be hereditary or acquired.

Chronic Conditions

Diseases like cancer, kidney disease, or autoimmune disorders can affect red blood cell production.

Comparison of Major Anemia Types and Causes

Here's a look at key differences between common causes of low Hgb.


Feature	Iron-Deficiency Anemia	Vitamin B12 Deficiency Anemia	Anemia of Chronic Disease
Primary Cause	Lack of iron	Inadequate B12	Chronic inflammation
Mechanism	Impaired Hgb production	Impaired red blood cell DNA synthesis	Inflammation suppresses red blood cell production
Common Triggers	Blood loss, poor diet, pregnancy	Poor diet, malabsorption	Kidney disease, cancer, autoimmune disorders
Red Blood Cell Size	Smaller than normal	Larger than normal	Normal size, initially
Treatment Focus	Iron supplements, treat blood loss	B12 injections/supplements	Treat underlying disease

Diagnosis and Treatment

Symptoms like fatigue or pale skin may prompt a complete blood count (CBC) to check Hgb levels. Further tests identify the cause. Treatment varies: iron deficiency may need supplements or addressing blood loss. Other anemias require tailored treatment, like B12 shots or managing a chronic illness. With proper diagnosis and treatment, the outlook is generally good.

Lifestyle and Dietary Adjustments

Eating iron-rich foods helps prevent or manage low Hgb from diet issues. Heme iron from meat is absorbed better than non-heme iron from plants. Vitamin C boosts non-heme iron absorption.

Consider these iron sources:

Heme Iron: Red meat, poultry, fish (like clams)
Non-Heme Iron: Beans, spinach, dried fruit, fortified grains

Pairing non-heme sources with vitamin C foods like oranges or broccoli enhances iron uptake.

Conclusion

Iron deficiency is the most common reason for low Hgb, primarily due to insufficient iron from diet, blood loss, or poor absorption. While other anemias exist from vitamin deficiencies, chronic diseases, or bone marrow issues, identifying and treating the root cause is crucial. Understanding iron's role and factors affecting Hgb helps manage health. For more information, the National Institutes of Health is a valuable resource(https://newsinhealth.nih.gov/).

Frequently Asked Questions

One of the most common signs of low Hgb is fatigue, a general feeling of being weak or tired. Other signs can include pale skin, headaches, shortness of breath, and a rapid heartbeat.

Yes, an inadequate diet lacking sufficient iron, vitamin B12, or folate can lead to low Hgb levels. However, low Hgb is also frequently caused by underlying issues like blood loss or malabsorption.

Significant or chronic blood loss is a common cause of low Hgb because it depletes the body's iron stores, which are necessary for producing hemoglobin. Common sources include heavy menstrual bleeding and internal bleeding from conditions like ulcers.

Low Hgb is diagnosed with a complete blood count (CBC), a standard blood test that measures hemoglobin levels. The specific cause is then determined through further evaluation, including additional blood tests and a review of symptoms and medical history.

Anemia is the medical term for having a low number of healthy red blood cells, which often results in a low Hgb count. Therefore, a low Hgb level is typically an indication of anemia.

Yes, pregnancy increases the body's blood volume and iron requirements. Without sufficient iron supplementation, many pregnant individuals develop iron-deficiency anemia, which results in low Hgb.

In some cases, yes. Endurance athletes can sometimes lose iron through gastrointestinal bleeding or the breakdown of red blood cells, a condition known as "march hemoglobinuria." This can lead to low Hgb and requires proper dietary management or supplementation.