This article is for educational purposes only and does not replace the advice of a qualified healthcare professional.
Iron deficiency is the most common nutritional deficiency in the world, affecting an estimated two billion people globally.
In the UK it is particularly prevalent among premenopausal women, children, adolescents, pregnant people, and those following plant-based diets, though it can affect anyone.
If you have been feeling persistently tired in a way that sleep does not fix, struggling with brain fog, feeling breathless with minimal exertion, noticing your hair falling out more than usual, or finding that your skin looks paler or more dull than normal, low iron could be a significant contributing factor.
Understanding what iron does, why levels drop, and what actually helps is the best place to start.
What Iron Does in the Body
Iron is essential for the production of haemoglobin, the protein in red blood cells that binds oxygen and transports it from the lungs to every cell in the body. It is also a key component of myoglobin, the protein that stores and delivers oxygen to muscle tissue.
Without adequate iron, less oxygen reaches the tissues, and the result is the characteristic fatigue, weakness, and reduced exercise tolerance of iron deficiency.
Beyond oxygen transport, iron plays essential roles in:
- energy metabolism
- immune function
- cognitive function
- the production of thyroid hormones
- the synthesis of neurotransmitters including dopamine and serotonin.
This is why the effects of iron deficiency extend well beyond physical tiredness to include mood changes, difficulty concentrating, irritability, and in children, impaired cognitive development.
Understanding the Different Measurements
This is where things get important, and where a lot of people fall through the gaps. There are several ways to measure iron status, and they do not all tell the same story.
Haemoglobin is the most commonly tested marker and is used to diagnose iron deficiency anemia. However, haemoglobin only falls when iron stores are severely depleted. By the time your haemoglobin is low, you have likely been iron deficient for some time.
Ferritin is the protein that stores iron in the body and is a much earlier and more sensitive marker of iron depletion. You can have a normal haemoglobin but very low ferritin, meaning you are not technically anaemic but your iron stores are running on empty. Many people in this situation experience significant symptoms and are told their blood results are "normal," which is technically true but clinically incomplete.
There is also ongoing debate in the research literature about what constitutes an optimal ferritin level. Standard laboratory reference ranges often include ferritin levels as low as 12 to 15 micrograms per litre as within the normal range, but some researchers and clinicians argue that optimal ferritin for symptomatic relief may be considerably higher, around 50 to 70 micrograms per litre or above.
If your ferritin has come back "normal" but you are still symptomatic, it is worth having a specific conversation about the actual number with your GP.
Serum iron and transferrin saturation are additional markers that can be measured alongside ferritin to give a fuller picture of iron status. If iron deficiency is suspected but ferritin alone is inconclusive, asking for a full iron panel is reasonable.
Why Iron Levels Drop
Iron deficiency develops when the body is losing or using more iron than it is absorbing from food. The most common reasons include:
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Menstruation is the single most common cause of iron deficiency in premenopausal women. Heavy periods in particular can cause significant monthly iron losses that are difficult to compensate through diet alone. If your periods are heavy and you are struggling with iron levels, it is worth discussing this with your GP, as managing menstrual blood loss may be as important as dietary and supplemental strategies.
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Pregnancy dramatically increases iron requirements, as the body is producing a much larger volume of blood and supplying iron to the developing baby and placenta. Iron deficiency anemia is one of the most common complications of pregnancy.
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Inadequate dietary intake, particularly in those following restrictive diets, very low calorie diets, or plant-based diets without careful attention to iron-rich foods.
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Poor absorption due to gut conditions including coeliac disease, inflammatory bowel disease, or low stomach acid. If you are consistently low in iron despite adequate intake and supplementation, absorption is worth investigating.
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Frequent blood donation, intense endurance exercise (which can cause haemolysis, or the breakdown of red blood cells), and certain medications including proton pump inhibitors, which reduce stomach acid and thereby impair iron absorption, are also relevant factors.
The Two Types of Dietary Iron
Not all dietary iron is equal, and understanding the difference between the two forms is genuinely important for managing iron levels through food.
Haem iron is found in animal products including red meat, poultry, and fish. It is bound to haemoglobin and myoglobin molecules and is absorbed directly and efficiently, with an absorption rate of around 15 to 35% regardless of the body's iron status or the presence of other dietary factors. It is the most bioavailable form of dietary iron.
Non-haem iron is found in plant foods including:
- lentils
- chickpeas
- kidney beans
- black beans
- tofu
- tempeh
- pumpkin seeds
- fortified cereals
- dark leafy greens including spinach
- dried apricots
- blackstrap molasses
It is also present in eggs and dairy, though in smaller amounts. Non-haem iron is far more variable in its absorption, ranging from as low as 2% to around 20%, depending heavily on what else is eaten alongside it and individual factors including iron status (the body absorbs more when stores are low) and stomach acid levels.
The Role of Vitamin C
This is one of the most well-established and practically useful findings in nutritional science: consuming vitamin C alongside non-haem iron significantly increases its absorption.
Vitamin C converts ferric iron (the form found in plant foods) into ferrous iron, which is the form the intestine can absorb. Research has found that consuming 25 to 75mg of vitamin C with a meal can increase non-haem iron absorption by two to four fold.
In practice this means:
- squeezing lemon juice over lentils
- adding red pepper or tomatoes to a bean-based dish
- having a glass of orange juice with iron-fortified porridge
- eating strawberries alongside a spinach salad.
These are simple, low-effort combinations that can make a meaningful difference to how much iron you actually absorb from plant-based meals.
This is particularly important for those following plant-based diets who are relying entirely on non-haem iron sources, but it is a useful principle for anyone looking to optimise their dietary iron intake.
What Inhibits Iron Absorption
Just as vitamin C enhances non-haem iron absorption, certain dietary factors significantly reduce it. Understanding these inhibitors does not mean avoiding them, but it does mean being thoughtful about timing.
Tannins
Found in tea and coffee, they are among the most significant inhibitors of non-haem iron absorption. A cup of tea drunk with a meal or immediately after it can reduce iron absorption by up to 60 to 70% according to research.
For people who are iron deficient or borderline, shifting tea and coffee to between meals rather than with them is a simple and evidence-based strategy that can make a real difference over time.
Calcium
Calcium competes with iron for absorption in the intestine. Consuming high-calcium foods (dairy products, fortified plant milks) or calcium supplements at the same meal as your main iron sources is therefore worth avoiding where possible.
This creates an interesting tension for those trying to meet both calcium and iron needs, and spacing them apart across the day is the most practical solution.
Phytates
Found in wholegrains, legumes, and nuts, bind to non-haem iron and reduce its absorption. Soaking, sprouting, and fermenting these foods reduces phytate content and improves mineral bioavailability.
Cooking legumes from dried (with soaking) rather than relying exclusively on tinned varieties can modestly improve iron absorption, though tinned legumes are still a valuable and convenient source.
Polyphenols
Polyphenols in certain plant foods including some vegetables, nuts, and cereals can also reduce non-haem iron absorption, though this effect is generally smaller than that of tannins and calcium.
Iron-Rich Foods Worth Knowing
Building meals around iron-rich foods is the foundation of dietary iron support.
Best animal sources
- beef
- lamb
- liver (which is exceptionally rich but should be limited in pregnancy due to high vitamin A content)
- dark poultry meat
- canned sardines
- canned tuna
- oysters
Best plant sources
- red lentils
- green lentils
- chickpeas
- kidney beans
- black beans
- edamame
- firm tofu
- pumpkin seeds
- hemp seeds
- fortified breakfast cereals (checking the label for iron content is worthwhile as amounts vary significantly)
- dried apricots
- raisins
- dark chocolate (above 70%)
- tahini
- spinach
Spinach deserves a specific mention because it is often cited as a top iron source, but its oxalate content significantly reduces the bioavailability of the iron it contains. It is still a valuable food and contributes to overall iron intake, but it should not be relied upon as a primary iron source, particularly for those who are deficient.
When Supplementation Is Needed
Dietary changes alone are not always sufficient to correct iron deficiency, particularly when deficiency is significant or when blood loss is ongoing. In these situations, supplementation is necessary and should be guided by a GP based on blood test results.
What to know
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Ferrous sulphate
the most commonly prescribed form and is effective, though it causes gastrointestinal side effects including nausea, constipation, and dark stools in many people.
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Ferrous gluconate and ferrous bisglycinate (also known as iron bisglycinate or gentle iron)
tend to be better tolerated with fewer GI side effects, though they are not always available on prescription and may need to be purchased over the counter.
Taking iron supplements on an empty stomach maximises absorption but can worsen nausea. Taking them with a small amount of food and a source of vitamin C is a reasonable compromise that may reduce side effects without dramatically compromising absorption.
Avoiding tea, coffee, and calcium-rich foods around the time of supplementation applies here as for dietary iron.
Alternate-day dosing for iron supplementation has emerged as an interesting area of research.
A study published in the Lancet Haematology found that alternate-day supplementation resulted in higher fractional iron absorption compared to daily dosing, because daily supplementation triggers a rise in hepcidin (a hormone that regulates iron absorption) that effectively blocks further absorption for the following 24 hours. This suggests that taking iron every other day may in some cases be more effective than daily dosing, though individual needs vary and any supplementation regimen should be discussed with a healthcare provider.
Monitoring and Follow-Up
If you are supplementing for confirmed iron deficiency, a follow-up blood test is important to check that levels are responding. Ferritin can take months to fully replete even with consistent supplementation, and it is worth continuing to supplement for a period after symptoms resolve to ensure stores are genuinely restored rather than just temporarily improved.
If iron levels are not responding to supplementation as expected, further investigation into absorption capacity, ongoing blood loss, or other contributing factors is warranted.
A Note on Self-Supplementing
It is worth being clear that iron supplementation without confirmed deficiency through blood tests is not recommended. Iron is not a benign supplement at higher doses: excess iron causes oxidative damage and gastrointestinal distress, and haemochromatosis, a genetic condition of iron overload, affects approximately one in 200 people of Northern European descent.
Taking iron supplements without knowing your iron status is not a safe precaution and can cause harm.
If you suspect iron deficiency based on symptoms, please get a blood test first.
Conclusion
Low iron levels are common, consequential, and in many cases very addressable.
Understanding the difference between haem and non-haem iron, the powerful role of vitamin C in enhancing absorption, and the key inhibitors to be mindful of gives you practical and evidence-based tools to meaningfully improve your iron status through diet.
Where dietary changes are not sufficient, targeted supplementation under medical guidance can make a significant and often rapid difference to how you feel.
Your energy, your mood, your concentration, and your physical capacity are all influenced by your iron status. If you have not had yours checked recently and any of this resonates, a simple blood test is an excellent place to start.
References:
https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/
Iron-rich-foods-iron-deficiency.html
https://www.mdpi.com/2072-6643/17/13/2132
