Iron deficiency anaemia occurs when the body does not have enough iron, leading to the decreased production of red blood cells.

Red blood cells carry oxygen around the body.

A lack of iron can be caused by several factors. Some of the most common causes of iron deficiency anaemia are outlined below.

Monthly periods

In women of reproductive age, periods are the most common cause of iron deficiency anaemia.

Usually, only women with heavy periods develop iron deficiency anaemia. If you have heavy bleeding over several consecutive menstrual cycles, it is known as menorrhagia.

Pregnancy

It is also very common for women to develop iron deficiency during pregnancy. This is because your body needs extra iron to ensure your baby has a sufficient blood supply and receives necessary oxygen and nutrients. Some pregnant women require an iron supplement and others may need to increase the amount of iron in their diet (see below).

Read more about vitamins and nutrition in pregnancy.

Gastrointestinal blood loss

Your gastrointestinal tract is the part of your body responsible for digesting food. It contains the stomach and intestines.

Bleeding in the gastrointestinal tract is the most common cause of iron deficiency anaemia in men, and in women who have been through the menopause (when monthly periods stop). Most people with gastrointestinal bleeding don’t notice any obvious blood in their stools and don’t experience any changes in their bowel habits.

Some causes of gastrointestinal bleeding are outlined below.

Non-steroidal anti-inflammatory drugs (NSAIDs)

Non-steroidal anti-inflammatory drugs (NSAIDs) can cause bleeding in the stomach. Ibuprofen and aspirin are two commonly prescribed NSAIDs.

If your GP thinks your medication is causing gastrointestinal bleeding, they can prescribe a less harmful medicine. Do not stop taking a medicine you have been prescribed unless your GP advises you to.

Stomach ulcers

The acid in your stomach (which helps your body to digest food) can sometimes eat into your stomach lining. When this happens, the acid forms an ulcer (an open sore). This is also known as a stomach ulcer (or a peptic ulcer).

Stomach ulcers can cause your stomach lining to bleed, which leads to anaemia. In some cases, this blood loss can cause you to vomit blood or pass blood in your stools (faeces). However, if the ulcer bleeds slowly, you may not have any symptoms.

Gastrointestinal cancer

In a few cases, gastrointestinal bleeding can be caused by cancer, usually of the stomach or colon.

When diagnosing the cause of anaemia, your GP will check for possible signs of cancer. If your GP suspects cancer, you will be referred to a gastroenterologist (a specialist in treating digestive conditions) for a more thorough examination. This means that if cancer is found, it can be treated as quickly as possible.

Read more about stomach cancer and bowel cancer.

Angiodysplasia

Gastrointestinal bleeding can also be caused by a condition called angiodysplasia. This is due to abnormal blood vessels in the gastrointestinal tract, which can cause bleeding.

Chronic kidney disease

Many people with chronic kidney disease (CKD) develop iron deficiency anaemia.

Most people with CKD who have iron deficiency anaemia will be given iron supplement injections, although daily tablets may be tried first.

Read more information from the National Institute of Health and Care Excellence (NICE) on treating anaemia in people with chronic kidney disease.

Other causes

Other conditions or actions that cause blood loss and may lead to iron deficiency anaemia include:

• inflammatory bowel disease – a condition that causes inflammation (redness and swelling) in the digestive system, such as Crohn’s disease and ulcerative colitis 
• oesophagitis – inflammation of the gullet (oesophagus) caused by stomach acid leaking through it
• schistosomiasis – an infection caused by parasites and mainly found in Sub-Saharan Africa
• blood donation – donating a large amount of blood may lead to anaemia
• trauma – a serious accident, such as a car crash, may cause you to lose a lot of blood 
• nosebleeds – if you have a lot of nosebleeds, this may lead to anaemia, although this is rare
• haematuria (blood in your urine) – although this rarely causes anaemia and may be a symptom of another condition

Malabsorption

Malabsorption (when your body cannot absorb iron from food) is another possible cause of iron deficiency anaemia.

This may happen if you have coeliac disease (a common digestive condition, where a person has an adverse reaction to gluten) or surgery to remove your stomach (gastrectomy).

Lack of iron in your diet

Unless you are pregnant, it is rare for iron deficiency anaemia to be caused solely by a lack of iron in your diet. However, a lack of dietary iron can make you more likely to develop anaemia if you also have any of the conditions mentioned above.

Some studies suggest vegetarians or vegans are more at risk of iron deficiency anaemia, due to the lack of meat in their diet. However, it is possible to gain enough iron in a vegetarian or vegan diet through other types of food, such as:

• beans
• nuts
• dried fruit, such as dried apricots
• wholegrains, such as brown rice
• fortified breakfast cereals
• soybean flour
• most dark-green leafy vegetables, such as watercress and curly kale

Pregnant women may have to increase the amount of iron-rich food they consume during their pregnancy to help avoid iron deficiency anaemia.

Read more about vegetarian and vegan diets and good sources of iron.