What causes anaemia?
The causes differ for the different types of anaemia.
This type of anaemia is caused by insufficient dietary intake of iron, reduced absorption of the iron that is consumed, or blood loss.
Insufficient iron intake:
In first-world settings, inadequate iron intake is uncommon as the sole cause of anaemia – the amount of iron in the diet is usually sufficient. It may, however, contribute to the development of anaemia in the setting of blood loss.
More iron is found in meat sources than in plant foods, and it’s better absorbed, as is iron in an acidic environment. Certain foods contain substances that may impair iron absorption. These include the tannates in tea; the phosphates and phytates in whole grains and seeds; as well as calcium.
In a country like South Africa, insufficient intake may indeed be the cause of iron deficiency. This is especially the case with children, where there’s a higher prevalence of malnutrition than in first-world countries. It’s also seen in infants who are weaned onto cow’s milk too early.
In most adult cases, it’s not safe to assume that iron deficiency is due solely to inadequate iron intake and a search should be undertaken for a source of blood loss.
This may be obvious, as in the case of heavy menstrual bleeding or recent childbirth. Another cause may be bleeding into the digestive tract as a result of an ulcer in the stomach or small intestine, a tumour or haemorrhoids. These can all result in blood in the stool or diarrhoea with black, tarry stools (melaena).
Frequently, the source of bleeding isn’t obvious. Causes that can be overlooked include:
- Frequent blood donation
- Excessive diagnostic blood testing
- Underestimation of heavy bleeding during menstruation
- Bleeding into the digestive tract that doesn’t produce obvious symptoms
- Hookworm and tapeworm infestation in children
Impaired iron absorption:
In conditions where the digestive tract isn’t functioning correctly, iron cannot be absorbed.
A number of factors determine the efficiency of iron absorption and certain medical conditions may interfere with this. These included coeliac disease, atrophic gastritis, lack of stomach acid due to antacid medication, gastric bypass surgery for weight loss and chronic diarrhoea.
Damage to the bone marrow’s stem cells causes aplastic anaemia. In more than half of people who have this type of anaemia, the cause of the disorder is unknown.
A number of diseases, conditions and factors can cause aplastic anaemia, including:
- Toxins such as pesticides, arsenic and benzene
- Radiation and chemotherapy
- Medicines such as chloramphenicol
- Infectious diseases such as hepatitis, Epstein-Barr virus, cytomegalovirus, parvovirus B19, and HIV
- Autoimmune disorders such as lupus and rheumatoid arthritis
Inherited conditions, such as Fanconi anaemia, Shwachman-Diamond syndrome, dyskeratosis congenital and Diamond-Blackfan anaemia may also cause aplastic anaemia.
The immediate cause of haemolytic anaemia is the premature destruction of red blood cells.
A number of diseases, conditions, and factors can cause the body to destroy its red blood cells. These causes can be inherited or acquired. Sometimes, the cause of haemolytic anaemia isn't known.
In inherited haemolytic anaemias, the genes that control how red blood cells are made are faulty. Different types of faulty genes account for the different types of inherited haemolytic anaemias. In each type of inherited haemolytic anaemia, the body makes abnormal red blood cells. The problem with the red blood cells may involve the haemoglobin, cell membrane, or enzymes that maintain healthy red blood cells.
In acquired haemolytic anaemias, the body makes normal red blood cells. However, some disease, condition or factor destroys the cells too early. Examples include autoimmune disorders (e.g. lupus/SLE), infections (e.g. infectious mononucleosis/glandular fever), certain cancers (e.g. lymphoma), and reactions to medicines or blood transfusions.
Haemoglobin in red blood cells has two kinds of protein chains: alpha globin and beta globin.
If your body doesn’t make enough of these protein chains, red blood cells don’t form properly and can’t carry enough oxygen. Genes control how the body makes haemoglobin protein chains. When these genes are missing or altered, thalassaemias occur.
Thalassaemias are inherited disorders – i.e. they’re passed on from parents to their children through genes. People who get abnormal haemoglobin genes from one parent but normal genes from the other are carriers. Carriers often have no signs of illness other than mild anaemia.
However, they can pass the abnormal genes on to their children.
Sickle cell anaemia
Sickle cell anaemia is an inherited, lifelong disease.
People who have the disease inherit two copies of the sickle cell gene – one from each parent – which lead to the production of abnormal haemoglobin and red cells.
Pernicious anaemia occurs due to vitamin B12 deficiency.
In this condition the body produces antibodies against "intrinsic factor": the protein produced by the stomach that binds to vitamin B12 and facilitates its absorption. Without intrinsic factor, vitamin B12 cannot be absorbed.
Your vitamin B12 levels may also be low because your small intestine cannot properly absorb vitamin B12. This may be linked to a bacterial imbalance in the small intestines; certain diseases that interfere with vitamin B12 absorption; certain medicines; surgical removal of part of the small intestine; or tapeworm infection.
Sometimes people have low vitamin B12 levels because they don’t get enough vitamin B12 through their diet. As vitamin B12 is mainly found in animal products such as meat, poultry, fish, eggs and milk, vegans and vegetarians are at risk for this type of anaemia if they don’t consume fortified foods such as cereals.
Fanconi anaemia (FA) is an inherited disease that’s passed on from parents to children through the genes. At least 13 faulty genes are associated with FA.
FA develops when both parents pass the same faulty FA gene to their child. People who have only one faulty gene are FA carriers. This means they don't have FA, but they can pass the faulty gene on to their children.
Anaemia of chronic disease
This type of anaemia occurs as a result of a combination of factors: reduced absorption of iron, inability of the bone marrow to produce more red blood cells, and decreased red cell survival.
Increased levels of hepcidin (a protein produced in the body in response to inflammation) leads to reduced iron absorption from the digestive tract and lower levels of iron available in the body for haemoglobin synthesis.
Reviewed by Cape Town-based general practitioner, Dr Dalia Hack. October 2018.