What Is Anemia: Causes, Types, Symptoms, and Treatment Options

This article is for informational purposes only. Consult a qualified healthcare professional for medical advice, diagnosis, or treatment.

What Is Anemia?

Anemia is a condition in which the blood contains insufficient healthy red blood cells (RBCs) or hemoglobin to carry adequate oxygen to the body's tissues. The World Health Organization defines anemia as a hemoglobin level below 13 g/dL in adult males and below 12 g/dL in adult non-pregnant females. Globally, anemia affects approximately 1.62 billion people—nearly 25% of the world's population—making it one of the most prevalent nutritional and hematological disorders worldwide. Women of reproductive age and young children bear the greatest burden.

How Red Blood Cells and Hemoglobin Work

Red blood cells are produced in the bone marrow and live approximately 120 days before being cleared by the spleen. Each RBC contains roughly 270 million molecules of hemoglobin—a protein built around iron that binds oxygen in the lungs and releases it in peripheral tissues. Anemia develops when RBC production falls, destruction accelerates, or blood loss depletes the circulating pool faster than the marrow can compensate.

Classification and Major Types

Causes and Risk Factors

The underlying cause of anemia determines its classification and treatment. The most common causes include:

• Dietary deficiency: Inadequate intake of iron, vitamin B12, or folate is the leading cause worldwide, particularly in developing countries and among vegetarians or vegans.
• Blood loss: Heavy menstrual periods, gastrointestinal bleeding (ulcers, colorectal cancer, NSAIDs use), or traumatic injury deplete iron stores rapidly.
• Malabsorption: Conditions like celiac disease, Crohn's disease, or gastric bypass surgery impair nutrient absorption in the small intestine.
• Hemolysis: Accelerated RBC destruction occurs in sickle cell disease, autoimmune hemolytic anemia, G6PD deficiency, and malaria.
• Bone marrow disorders: Aplastic anemia, myelodysplastic syndromes, leukemia, or chemotherapy can suppress RBC production directly.
• Chronic disease: Kidney disease (reduced erythropoietin), rheumatoid arthritis, HIV, and cancer are frequent underlying causes in developed nations.

Symptoms

The severity of symptoms correlates with both the degree of anemia and the speed of its onset. Gradual-onset anemia allows physiological compensation, so patients may tolerate surprisingly low hemoglobin before becoming symptomatic. Common symptoms include:

• Fatigue and general weakness—the most universal complaint
• Pallor of the skin, conjunctiva, and nail beds
• Shortness of breath on exertion
• Heart palpitations and tachycardia as the heart compensates by pumping faster
• Dizziness, headache, and difficulty concentrating
• Cold hands and feet due to peripheral vasoconstriction
• Pica (craving ice, dirt, or starch)—classic in iron-deficiency anemia
• Glossitis (sore, smooth tongue) and angular cheilitis in B12/folate deficiency

Diagnosis

Diagnosis begins with a complete blood count (CBC), which measures hemoglobin, hematocrit, RBC count, mean corpuscular volume (MCV), and reticulocyte count. MCV directs the differential: microcytic anemia (low MCV) points to iron deficiency or thalassemia; normocytic anemia suggests chronic disease or hemolysis; macrocytic anemia indicates B12 or folate deficiency. Additional tests include serum iron, ferritin, transferrin saturation, peripheral blood smear, and, when indicated, bone marrow biopsy.

Treatment by Type

Outlook and Prevention

Most nutritional anemias respond well to supplementation and dietary changes within weeks to months. Iron-deficiency anemia, the world's most common micronutrient deficiency, is largely preventable through food fortification, supplementation programs, and improving dietary diversity. Inherited anemias like sickle cell disease require lifelong management, but advances in gene therapy—including CRISPR-based approaches—offer the prospect of eventual curative treatments. Regular monitoring of hemoglobin levels in at-risk populations (pregnant women, infants, elderly) enables early intervention before symptoms become debilitating.