Iron deficiency anaemia: what to eat and how to improve iron absorption

What is iron deficiency anaemia, and why is eating better not enough?

Iron deficiency anaemia develops when iron stores are depleted and the bone marrow cannot make enough haemoglobin. This blood protein carries oxygen. The Organización Mundial de la Salud defines anaemia as haemoglobin below 120 g/L in non-pregnant adult women [3]. The same organisation considers serum ferritin below 15 µg/L to indicate depleted iron stores in a healthy adult woman [4]. If you still do not know why your haemoglobin is low, its guide explains which data help interpret it. See “Anaemia in pregnancy”.

To understand why food alone is not enough, it helps to distinguish two things. Ferritin is the storage depot; haemoglobin is the vehicle that delivers oxygen. When the depot is empty and haemoglobin falls, hundreds of milligrams of iron are missing. The intestine absorbs only a small fraction of the iron supplied by food each day.

That is why anyone with iron deficiency anaemia should receive iron treatment prescribed by their doctor. The Sociedad Británica de Gastroenterología guideline says treatment should not be delayed until investigations into the cause are complete [2]. Food is essential to support the process and maintain stores once restored, but it does not replace treatment.

What is the difference between haem and non-haem iron?

Food contains two forms of iron: haem and non-haem. The body uses them quite differently.

Haem iron is found in meat, poultry, fish and seafood. It is part of haemoglobin and myoglobin. According to the Autoridad Europea de Seguridad Alimentaria, its absorption depends little on the rest of the meal, although calcium does reduce it [1]. That makes it the most reliable source when stores are low.

Non-haem iron is found in plant foods (pulses, nuts, seeds, grains and vegetables) and eggs. It is absorbed less efficiently and varies considerably. The same European authority explains that absorption depends on a balance: vitamin C helps, while phytates and polyphenols reduce it [1]. This balance can guide how you combine foods.

Which foods contain the most iron, and how should you spread them through the week?

To ensure a regular intake, vary your sources throughout the week. You can combine foods from both groups. See “Fibroids and food”.

Among animal foods, bivalve molluscs are especially rich in haem iron: clams, cockles, mussels and striped venus clams. They provide substantial amounts in moderate portions. Next come sardines, tuna and mackerel. Also beef, chicken, turkey and rabbit, which provide good-quality protein.

Among plant foods, pulses (lentils, chickpeas, white or pinto beans, and soya products) are the main source of non-haem iron. Pistachios, almonds, pumpkin seeds and sesame also contribute. Oats are another source. Spinach and chard contain iron, but their oxalic acid binds much of it. They contribute, but not as the meal’s main source. Egg yolk also provides iron; pair it with fresh vegetables rich in vitamin C.

Which combinations improve the absorption of plant iron?

Because non-haem iron is less readily absorbed, pair it with foods that help absorption.

The best-supported enhancer is vitamin C (ascorbic acid). It converts iron into a more soluble form that the intestine can absorb more easily. The Autoridad Europea de Seguridad Alimentaria notes that the effect increases with the amount of vitamin C in the meal [1]. In practice, include a vitamin C-rich food in the same meal. This can be raw red pepper in a salad, a kiwi, an orange, two mandarins or a handful of strawberries for dessert.

A little meat or fish in the same dish improves absorption of iron from pulses. This is known as the “meat factor”. A classic example is lentil stew with pepper and tomato, a squeeze of lemon or citrus fruit for dessert.

Which foods reduce or block iron absorption?

Some compounds in nutritious foods bind to non-haem iron and make it harder for the intestine to absorb.

The Autoridad Europea de Seguridad Alimentaria identifies several inhibitors. These include polyphenols in tea, coffee, cocoa and red wine. Also phytates in whole grains and pulses, and calcium in dairy foods and supplements [1]. Calcium is also one of the few substances that reduces absorption of haem iron [1].

The answer is not to eliminate these foods, but to have them at a different time. The Sociedad Británica de Gastroenterología guideline reports that tea’s inhibitory effect disappears after about 60 minutes [2]. Keeping coffee, tea and dairy foods at least an hour away from main meals is a simple approach. You can have coffee mid-morning or yoghurt as a snack without reducing the iron from your meal.

How are heavy periods and pregnancy linked to iron?

In women of reproductive age, low iron is rarely caused only by eating too little iron. Menstrual blood loss and increased needs during pregnancy matter more.

The Sociedad Británica de Gastroenterología guideline lists three main factors in younger women: menstrual blood loss, pregnancy and a diet low in iron [2]. With heavy periods, monthly iron loss can exceed what food replaces. Your doctor or gynaecologist should assess the cause and treatment.

During pregnancy, iron needs increase to support blood volume, the placenta and the baby’s growth. This happens especially in the second half. The OMS recommends iron supplementation for all pregnant women. In Spain, your care team will decide on the regimen based on your blood tests. If you are pregnant, see our specific guidance on diet during pregnancy and our specialist pregnancy nutrition service.

What mistakes do we see in consultations when people take iron supplements?

Ongoing tiredness often leads people to buy iron supplements on their own, but taking them without blood tests has drawbacks.

The body has no active way to remove excess iron, and prolonged excess can damage tissues. The Sociedad Británica de Gastroenterología reports that digestive side effects are clearly more common with oral iron than with placebo. These include nausea, stomach pain, constipation and diarrhoea [2]. Taking a supplement without a diagnosis may also conceal blood loss that needs investigation.

For these reasons, your doctor decides the type of iron, dose and duration based on blood tests. The dietitian-nutritionist helps you fit the dose into your daily routine in line with the medical plan. They can space it from dairy foods, coffee and tea, and adjust fibre and fluids. This makes the treatment easier to tolerate and avoids stopping it. The same British guideline does not recommend routinely adding vitamin C to the iron tablet [2].