What Is Anaemia and How Does It Develop
Anaemia occurs when your blood does not have enough healthy red blood cells or haemoglobin to carry oxygen throughout your body. Haemoglobin is a protein in red blood cells that binds to oxygen and transports it from your lungs to every tissue and organ. When haemoglobin levels drop below normal ranges—typically below 13.5 grams per decilitre for men and below 12 grams per decilitre for women—your body cannot distribute oxygen efficiently.
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Red blood cells live for approximately 120 days before your body removes them and creates new ones. Your bone marrow constantly produces new red blood cells to replace old ones. Anaemia develops when this balance breaks down—either your body destroys or loses red blood cells faster than it can replace them, or your bone marrow cannot produce enough new cells. The World Health Organization estimates that over 2 billion people worldwide have anaemia, making it one of the most common blood disorders.
Your body needs specific nutrients to produce healthy red blood cells, particularly iron, vitamin B12, and folate. These nutrients work together in a complex process called erythropoiesis. Iron forms the core of haemoglobin molecules. Vitamin B12 helps your bone marrow create red blood cells with proper structure. Folate assists in DNA synthesis during cell division. Without adequate amounts of these nutrients, your bone marrow produces fewer red blood cells or creates cells that function poorly.
Anaemia is not a disease itself but rather a sign that something else is happening in your body. It can range from mild cases that barely affect daily life to severe cases requiring immediate medical attention. Understanding how anaemia develops helps you recognize when something may be wrong and why different types require different treatment approaches.
Practical takeaway: Anaemia means your blood lacks enough healthy red blood cells to carry oxygen properly. This happens when your body cannot make cells fast enough, loses cells too quickly, or lacks nutrients needed for cell production.
Iron Deficiency Anaemia: The Most Common Type
Iron deficiency anaemia accounts for approximately 50 percent of all anaemia cases globally. This type develops when your body does not have enough iron to produce adequate haemoglobin. Iron is essential because it sits at the centre of every haemoglobin molecule. Without sufficient iron, your bone marrow cannot manufacture enough functional red blood cells, even if all other processes work correctly.
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Your body obtains iron through diet and recycles iron from old red blood cells. Red meat, poultry, fish, beans, lentils, fortified cereals, and leafy greens contain iron. However, the type of iron matters—haem iron from animal sources absorbs more efficiently (15-35 percent absorption) than non-haem iron from plant sources (2-20 percent absorption). This is why people following vegetarian or vegan diets need to consume larger quantities of iron-containing foods or consider supplements.
Iron deficiency anaemia develops through several pathways. Chronic blood loss is the most common cause in developed countries. Heavy menstrual bleeding affects millions of women and remains a leading cause of iron deficiency. Gastrointestinal bleeding from ulcers, hemorrhoids, or inflammatory bowel disease can also deplete iron stores. Some people simply do not consume enough dietary iron, particularly older adults with poor appetite or those with limited food access. Pregnancy increases iron demands significantly—pregnant women need roughly double the normal iron intake because their blood volume expands and the developing fetus requires iron.
Children aged 1-3 years are particularly vulnerable to iron deficiency because they grow rapidly and often consume limited iron-rich foods. In developing countries, parasitic infections that cause intestinal bleeding account for substantial iron loss. Certain medical procedures, like frequent blood donations without adequate recovery time, can also deplete iron stores.
Practical takeaway: Iron deficiency anaemia is the most common type and typically results from blood loss, inadequate dietary intake, increased demands during pregnancy or growth, or absorption problems. Including more iron-rich foods in your diet—particularly those containing haem iron from animal sources—can help prevent this type.
Vitamin B12 and Folate Deficiency Anaemia
Vitamin B12 and folate work together to maintain healthy red blood cell production. When either nutrient is deficient, your bone marrow produces fewer red blood cells and creates larger, abnormal cells called megaloblasts. This results in macrocytic anaemia, where red blood cells are larger than normal but fewer in number. The body's oxygen-carrying capacity drops because it has fewer cells to transport oxygen, even though individual cells may contain more haemoglobin.
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Vitamin B12 comes exclusively from animal sources—meat, fish, poultry, eggs, and dairy products contain B12. People following strict vegan diets without B12 supplementation or fortified foods face significant risk of deficiency. However, dietary inadequacy accounts for only a small percentage of B12 deficiency cases. Most cases result from absorption problems. Pernicious anaemia, an autoimmune condition, occurs when your stomach cannot produce intrinsic factor, a protein necessary for B12 absorption. Approximately 1-2 percent of older adults develop pernicious anaemia. Gastrointestinal surgery, particularly procedures that remove part of the stomach or small intestine, also reduces B12 absorption capacity. Some medications, including metformin used for diabetes and proton pump inhibitors for acid reflux, interfere with B12 absorption when taken long-term.
Folate comes from leafy green vegetables, legumes, asparagus, Brussels sprouts, and fortified grains. Unlike B12, folate absorption problems are less common—most folate deficiency results from inadequate intake. Pregnant and breastfeeding women need significantly more folate (400-600 micrograms daily) because folate is essential for fetal development and preventing neural tube defects. Alcohol abuse damages the small intestine's ability to absorb and store folate. Some medications, including anticonvulsants and methotrexate, interfere with folate metabolism.
B12 and folate deficiency anaemia develops gradually over months or years because your body stores these nutrients in the liver. A person can have adequate blood levels while depleting stored reserves. This delayed onset means deficiency often goes unrecognized until symptoms become pronounced. Unlike iron deficiency, which primarily affects oxygen transport, B12 and folate deficiency also affects nerve function because these vitamins are crucial for nerve cell maintenance.
Practical takeaway: B12 and folate deficiency anaemia develops when your body lacks these nutrients or cannot absorb them properly. Including animal products, leafy greens, and legumes in your diet helps prevent these types. People with certain medical conditions or taking specific medications may need to monitor B12 and folate levels more carefully.
Other Important Causes of Anaemia
Beyond iron, B12, and folate deficiency, numerous other conditions can trigger anaemia. Chronic kidney disease accounts for a substantial portion of anaemia cases, particularly in older adults. The kidneys produce erythropoietin (EPO), a hormone that signals bone marrow to produce red blood cells. When kidney function declines, EPO production drops, reducing red blood cell production. In developed countries, chronic kidney disease affects approximately 13 percent of the population, and anaemia complicates roughly 40 percent of these cases.
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Chronic diseases including diabetes, rheumatoid arthritis, cancer, and heart disease frequently cause anaemia through multiple mechanisms. Inflammation associated with these conditions suppresses bone marrow activity and increases red blood cell destruction. Cancer treatment through chemotherapy and radiation directly damages bone marrow, temporarily halting or reducing red blood cell production. Some cancer medications specifically target rapidly dividing cells, which includes bone marrow cells. These treatment-related anaemias typically improve after treatment concludes, though recovery varies.
Haemolytic anaemia develops when red blood cells are destroyed faster than normal, before their typical 120-day lifespan ends. This can result from autoimmune conditions where the body attacks its own red blood cells, hereditary conditions like sickle cell disease or thalassaemia, or acquired causes like infections or certain medications. Sickle cell disease affects approximately 100,000 Americans, with higher prevalence in people of African descent, while thalassaemia primarily affects people with Mediterranean, Middle Eastern, and Asian ancestry.
Bone marrow disorders directly impair red