Most people think about iron when they feel tired, and it’s more relevant for females, too, in this context.

Iron is essential for making haemoglobin, the protein in red blood cells that helps carry oxygen around the body. When iron is low, fatigue, weakness, breathlessness, dizziness and reduced exercise tolerance can be some of the first things people notice.

But iron is not just an energy/fatigue nutrient. It’s also involved in brain function, neurotransmitter production, dopamine signalling, thyroid hormone metabolism, mitochondrial energy production, immune function, muscle performance, sleep quality and restless legs syndrome. This is why low iron can sometimes show up as brain fog, poor concentration, low mood, feeling wired but exhausted, poor sleep, restless legs or anxiety-like symptoms.

That does not mean every tired, anxious or foggy person has low iron. Symptoms overlap with stress, poor sleep, thyroid issues, low B12, low vitamin D, under-eating, heavy training, chronic inflammation, alcohol history, gut issues, medications, pregnancy, postpartum depletion and many other causes, the list goes on.

In this article, we’ll unpack iron, including it’s simple role as a “fatigue” nutrient, and also beyond so that you can understand it further.

What To Know (Article Snapshot)

• Iron helps carry oxygen through haemoglobin and supports oxygen use in muscles through myoglobin.
• Iron is also involved in cellular energy production, thyroid hormone metabolism, neurotransmitter synthesis and brain development.
• Low iron can exist before anaemia shows up on a standard full blood count.
• Ferritin is commonly used to assess iron stores, but it needs to be interpreted in context because inflammation can raise ferritin.
• Low iron may contribute to fatigue, reduced exercise tolerance, poor concentration, low mood, restless legs, poor sleep and anxiety-like symptoms in some people.
• Restless legs syndrome has one of the stronger links with iron regulation, especially brain iron and dopamine pathways.
• Iron supplements should not be taken casually without testing and guidance. Too much iron can be harmful.

Why Does Low Iron = Low Energy & Fatigue?

Iron is best known for transporting oxygen through-out the body.

Your body uses iron to make haemoglobin, which carries oxygen from the lungs through the bloodstream. Iron is also part of myoglobin, which helps muscles access and use oxygen. So, without iron, these two functions don’t operate per usual, leading to fatigue (NIH Office of Dietary Supplements).

So, all the talk on iron deficiency and fatigue is warranted, iron matters for energy.

But, that’s only the small part of the story.

Iron is also part of the enzymes and proteins that help generate cellular energy, regulate oxidative stress, and support normal neurological function,

When iron status is low, we present with symptoms related to fatigue. It may look like heavy limbs, brain fog, poor motivation, or reduced stress resilience.

Low Iron Is Not Always The Same As Anaemia

This is one of the most important points.

A person can have low iron stores without being anaemic.

Anaemia usually refers to low haemoglobin or a reduced ability of the blood to carry oxygen. Iron deficiency can eventually lead to iron deficiency anaemia, but iron stores may fall before haemoglobin drops below range.

This is where ferritin becomes useful. Ferritin is a protein that stores iron. Low ferritin often suggests depleted iron stores.

Australian Prescriber notes that non-anaemic iron deficiency is common, can cause non-specific symptoms, and is usually seen as low ferritin and low transferrin saturation with normal haemoglobin (Australian Prescriber).

That does not mean ferritin is the only marker that matters. Ferritin can rise with inflammation, infection, liver disease and other contexts, so a result that looks normal does not always tell the whole story.

This is why we generally want to look at the whole picture, and and also assess other factors including inflammatory markers, menstrual loss, diet, lifestyle, and more. (Auerbach et al., 2025)

When iron is low, we should be asking, why is it low and what else is happening around it?

Iron And The Brain

Iron is present throughout the brain and is involved in several processes that matter for cognition, mood, movement and nervous-system function.

A systematic review on women of childbearing age found evidence linking iron deficiency with poorer cognition, mental health scores and fatigue in several studies (Greig et al., 2013).

Although the authors noted more research is warranted, it does underscore the link on iron and brain function. It suggests that iron status can be relevant when someone presents with persistent fatigue, brain fog, low concentration, reduced motivation or mood changes.

If we look further, we can begin to see irons critical role in neurotransmitter synthesis and long-term nerve function.

Iron, Dopamine and Serotonin

Iron is a vital co-factor for enzymes involved in synthesising two key neurotransmitters, Dopamine and Serotonin.

These two fairly well known neurotransmitters are heavily involved in regulating our mood, motivation, focus, hunger and drive (to note a few).

In plain English, iron is part of the biochemical step to make these. When iron status insufficient, we see alterations in dopamine pathways, and impacts in emotional regulation and mood (Pivina et al., 2019).

Interestingly, we also need adequate iron for long-term nerve health. Iron is required for the production of myelin (the coating around our nerves). Some studies suggest early-life iron deficiency can impact this long-term, leading to deficits in neural development (Gao et al., 2025).

Iron And Restless Legs

Restless legs syndrome is one of the strongest reasons to think about iron beyond fatigue.

Restless legs can feel like an uncomfortable urge to move the legs, usually worse at rest or in the evening. It can make sleep difficult and leave someone exhausted during the day.

Iron regulation, brain iron and dopamine pathways are central to current discussions of restless legs syndrome. A 2025 review describes the link between iron deficiency and restless legs syndrome and explains how altered iron metabolism may contribute to the condition (Rizvi et al., 2025). A 2025 article in Sleep notes that iron dysregulation in the brain is now thought to play a fundamental role in the pathophysiology of restless legs syndrome (Sleep).

The American Academy of Sleep Medicine’s clinical practice guideline also recommends iron treatment in specific restless legs contexts where iron indices are appropriate, particularly intravenous ferric carboxymaltose for adults with restless legs syndrome and suitable iron status (AASM guideline summary on PubMed).

This does not mean everyone with restless legs should start iron. It means iron studies are often clinically relevant, especially when symptoms affect sleep.

For the average person, the useful takeaway is this: if you have restless legs, poor sleep and fatigue, it may be worth checking ferritin and full iron studies rather than assuming it is just stress, ageing or poor sleep hygiene.

Iron, Thyroid Function And Metabolism

Iron is also relevant to thyroid physiology.

Thyroid peroxidase, an enzyme involved in thyroid hormone synthesis, is iron-dependent. This is one reason iron deficiency has been studied in relation to thyroid function.

A 2023 systematic review and meta-analysis reported relationships between iron deficiency and thyroid function, including differences in TSH, free T4 and free T3 in some groups, particularly pregnant women and women of reproductive age (Garofalo et al., 2023). A 2021 systematic review and meta-analysis also examined iron deficiency as a risk factor for thyroid disorders in reproductive-age and pregnant women (Luo et al., 2021).

This means iron should be used as part of the bigger picture when someone is presenting with fatigue, cold sensitivity, low mood, hair loss. Thyroid function, iron status, inflammation, menstrual blood loss, protein intake, iodine, selenium, stress and sleep can all overlap.

Low Iron and Anxiety

Low iron can contribute to anxiety in a few overlapping ways.

The first is through oxygen delivery. When iron is low, the body may have a harder time making enough haemoglobin and moving oxygen efficiently. That can lead to symptoms such as racing heart, palpitations, shortness of breath, dizziness, poor exercise tolerance and feeling physically unsettled (Healthdirect Australia).

The second pathway is through the brain. Iron is involved in brain energy metabolism, myelination and monoamine neurotransmitter metabolism, including dopamine and serotonin pathways (Kim & Wessling-Resnick, 2014).

As mentioned previously, These neurotransmitters help regulate mood, motivation, focus, emotional steadiness and stress response. When iron availability is poor, these pathways may not function as smoothly, leading to anxiety.

One study in children with iron deficiency anaemia found changes in plasma dopamine, serotonin and brain-derived neurotrophic factor in response to variation in iron availability (Bani-Ahmad et al., 2022).

There is also emerging genetic evidence supporting a relationship between iron status and anxiety risk. A 2024 Mendelian randomisation study found that genetically predicted iron status biomarkers were linked with anxiety disorder risk (Yin et al., 2024).

Who Is More At Risk Of Low Iron?

Iron deficiency can happen because intake is low, needs are higher, absorption is reduced or losses are increased (if you were to look at it fundamentally).

Some common risk factors include:

• Heavy menstrual bleedin
• Pregnancy or postpartum recovery
• Vegetarian or vegan diets without careful planning
• Low overall food intake
• Endurance training or high training loads (Foot-strike hemolysis)
• Frequent blood donation
• Gut conditions that affect absorption
• Coeliac disease or inflammatory bowel disease
• Long-term use of some medications that affect stomach acid or gut function
• A history of iron deficiency
• Diets low in iron-rich foods, protein or vitamin C

If iron is low because of heavy menstrual bleeding, gut bleeding, poor absorption or inflammation, simply taking a supplement without understanding the reason can leave the issue unresolved, and does not address the root cause.

Food Sources Of Iron

There are two main types of dietary iron: haem iron and non-haem iron.

Haem iron is found in animal foods and is generally more readily absorbed. Non-haem iron is found in plant foods and fortified foods. The NIH notes that haem iron has higher bioavailability than non-haem iron, and that vegetarian diets usually have lower iron bioavailability than mixed diets containing meat, seafood and vitamin C-rich foods (NIH Office of Dietary Supplements).

The numbers below are approximate iron amounts per 100g. They can vary depending on the cut, cooking method, brand, fortification level and database used (Healthdirect Australia; Nutrition Australia; USDA FoodData Central).

Haem iron foods

• Beef: approximately 2.5-3.5mg per 100g
• Lamb: approximately 2.5mg per 100g
• Kangaroo: approximately 3.2-4.1mg per 100g
• Chicken: approximately 0.4-1.3mg per 100g
• Turkey: approximately 0.7-1.4mg per 100g, depending on white or dark meat
• Fish: approximately 0.3-1.3mg per 100g, depending on the fish
• Sardines: approximately 2.5-6.1mg per 100g, depending on whether canned or cooked/fried
• Tuna: approximately 1.1-1.5mg per 100g
• Oysters and mussels: approximately 6-9mg per 100g
• Liver or organ meats, where appropriate: approximately 6-11mg per 100g, depending on the type

Non-haem iron foods

• Lentils: approximately 3.3mg cooked or 9.1mg dry per 100g
• Chickpeas: approximately 1.8-2.9mg per 100g
• Beans: approximately 2-3mg per 100g, depending on the type
• Tofu: approximately 2.9mg per 100g
• Tempeh: approximately 2.7mg per 100g
• Pumpkin seeds: approximately 8-9mg per 100g
• Sesame seeds and tahini: sesame seeds approximately 14mg per 100g; tahini approximately 2-3mg per 100g
• Cashews: approximately 5mg per 100g
• Spinach and leafy greens: raw spinach approximately 3mg per 100g; cooked spinach can be higher per 100g because it is more concentrated
• Quinoa: approximately 1.5mg cooked or 4.6mg dry per 100g
• Iron-fortified cereals: varies widely, often approximately 8-16mg per serve depending on the product
• Whole grains: approximately 1-4mg per 100g, depending on the grain
• Dried apricots: approximately 3.1-6.3mg per 100g

Plant-based eaters can build iron-rich diets, but they usually need to be more intentional about absorption.

How To Improve Iron Absorption From Food

Iron absorption depends on the type of iron, the meal composition and the person’s current iron status.

Simple food-first strategies include:

• Pair plant-based iron foods with vitamin C, such as citrus, kiwi, berries, capsicum or tomato.
• Include haem iron foods if they fit your diet and values.
• Avoid drinking tea or coffee directly with iron-rich meals if iron status is low.
• Be mindful that calcium supplements can reduce iron absorption when taken at the same time.
• Build meals around protein, colourful plants and enough overall food, not just one iron-rich ingredient.

Harvard’s Nutrition Source notes that vitamin C and haem iron can improve non-haem iron absorption, while phytates, tannins and large amounts of calcium can inhibit non-haem iron absorption (Harvard T.H. Chan School of Public Health).

Why You Should Not Self-Prescribe Iron

While supplementing with iron can be the most simple solution, consuming too much iron is equally as harmful as consuming too little.

Having too much iron in the body is toxic and can be fatal, and this is because it’s highly oxidative (think of too much oxidation as cellular rust).

Some people are also at risk of iron overload conditions such as haemochromatosis. This condition involves the inability to metabolise and clear iron from the body as fast as most people These people often need to give blood or reduce iron consumption, so if you have this condition, you definitely do not want to be touching an iron supplement.

Some iron supplements can also cause constipation, nausea, stomach pain and digestive discomfort. Usually, this depends on the type of supplement and iron source you choose, so it’s always good to discuss with a health practitioner first before supplementing with iron.

A sensible approach to take before taking an iron supplement includes:

1. Test your iron levels first and understand your serum iron, ferritin and transferrin levels.
2. Discuss with a health professional to understand the broader scope or other causative factors.
3. Implement food first approaches alongside a good, bioavailable iron supplement.
4. Recheck levels at a later date to measure against your first test baseline.
5. Stop, reduce or adjust when appropriate.

When To Seek Professional Guidance

It is worth seeking guidance if you have ongoing symptoms such as:

• Fatigue that does not improve with rest
• Breathlessness on exertion
• Dizziness or light-headedness
• Poor concentration or memory issues
• Restless legs or sleep disruption
• Heavy menstrual bleeding
• Hair shedding with fatigue or low mood
• Reduced exercise tolerance
• Pale skin or unusual weakness
• A history of low ferritin or iron deficiency
• Gut symptoms, blood in stool or unexplained weight changes

It is especially important to seek medical care if symptoms are severe, new, worsening or linked with possible blood loss or fainting.

Seeking out a Naturopath or Nutritionist can help interpret your blood results in context with other factors that could be causative factors to your low iron and overall fatigue picture.

The Takeaway

Iron is bigger than energy and fatigue.

It helps carry oxygen, but it also supports cellular energy production, brain function, dopamine-related pathways, sleep, restless legs, thyroid physiology and nervous-system resilience.

That is why low iron can sometimes feel like more than tiredness. It may show up as fogginess, poor concentration, low motivation, poor sleep, restless legs, reduced exercise tolerance or feeling wired but depleted.

But symptoms alone are not enough to diagnose low iron.

The smart approach is to test, interpret the results properly and understand why iron may be low in the first place. Food can help. Absorption strategies can help. Supplements may be useful when there is a confirmed need. But iron should not be taken casually without testing and guidance.

If you are dealing with fatigue, brain fog, restless legs, poor sleep, low mood, heavy periods or reduced exercise tolerance, Stephen can help you look at the bigger picture: diet, iron intake, ferritin and iron studies, nervous-system load, sleep, stress, training, thyroid context and other nutrients that may be part of the pattern.

FAQ

Why is iron more than an energy nutrient?

Iron helps carry oxygen, but it is also involved in cellular energy production, brain function, neurotransmitter synthesis, dopamine pathways, thyroid hormone metabolism, immune function and nervous-system health. That is why low iron can affect more than fatigue.

Can low iron cause anxiety-like symptoms?

Low iron can sometimes contribute to symptoms that overlap with anxiety, such as shortness of breath, racing heart, restlessness, poor sleep, dizziness, fatigue and reduced stress tolerance. It is not the only possible cause, so testing and proper assessment matter.

What is ferritin?

Ferritin is a protein that stores iron. Low ferritin can suggest low iron stores, even when haemoglobin is still normal. Ferritin can also rise with inflammation or illness, so it should be interpreted alongside symptoms, full blood count, iron studies and health context.

Can you have low iron without being anaemic?

Yes. Iron stores can become low before haemoglobin drops low enough to be classified as anaemia. This is often called non-anaemic iron deficiency. It may still be associated with symptoms such as fatigue, poor concentration, reduced exercise tolerance or restless legs.

Can low iron affect sleep?

Low iron can be linked with restless legs syndrome, which can disrupt sleep. Low iron may also contribute indirectly to fatigue, restlessness or poor recovery. Sleep problems can have many causes, so iron is one possible factor to investigate.

What foods contain iron?

Animal sources include beef, lamb, poultry, fish, seafood and organ meats. Plant sources include lentils, beans, chickpeas, tofu, tempeh, pumpkin seeds, tahini, leafy greens, quinoa and iron-fortified cereals. Pairing plant iron with vitamin C-rich foods can improve absorption.

Should I take iron supplements without testing?

No. Iron supplements should not be taken casually without testing or professional guidance. Too much iron can be harmful, and symptoms of low iron can overlap with many other issues. It is better to confirm whether iron is low, understand the cause and use the right approach.

Is plant-based iron enough?

It can be, but plant-based eaters usually need to be more intentional. Plant foods contain non-haem iron, which is less readily absorbed than haem iron and more affected by meal composition. Vitamin C-rich foods, adequate protein and smart meal timing can help.

How long does it take to improve low iron?

It depends on the severity, cause, treatment approach, absorption, diet and whether ongoing blood loss is present. Some people feel better within weeks, while iron stores may take longer to rebuild. Follow-up testing helps confirm whether the plan is working.

References

American Academy of Sleep Medicine. (2025). Treatment of restless legs syndrome and periodic limb movement disorder: An American Academy of Sleep Medicine clinical practice guideline. https://pubmed.ncbi.nlm.nih.gov/39324694/

Auerbach, M., DeLoughery, T. G., & Tirnauer, J. S. (2025). Iron deficiency in adults: A review. JAMA, 333(20), 1813-1823. https://doi.org/10.1001/jama.2025.0452

Australian Prescriber. (2021). Non-anaemic iron deficiency. https://australianprescriber.tg.org.au/articles/non-anaemic-iron-deficiency.html

Bani-Ahmad, M., Ahmad, M., Obeidat, M., & Barqawi, M. (2022). The modulation of plasma levels of dopamine, serotonin, and brain-derived neurotrophic factor in response to variation in iron availability. Acta Biomedica, 93(6), e2022293. https://doi.org/10.23750/abm.v93i6.13276

Gao, Q., Zhou, Y., Chen, Y., Hu, W., Jin, W., Zhou, C., Yuan, H., Li, J., Lin, Z., & Lin, W. (2025). Role of iron in brain development, aging, and neurodegenerative diseases. Annals of Medicine, 57(1), 2472871. https://doi.org/10.1080/07853890.2025.2472871

Garofalo, V., Condorelli, R. A., Cannarella, R., Aversa, A., Calogero, A. E., & La Vignera, S. (2023). Relationship between iron deficiency and thyroid function: A systematic review and meta-analysis. https://pubmed.ncbi.nlm.nih.gov/38004184/

Greig, A. J., Patterson, A. J., Collins, C. E., & Chalmers, K. A. (2013). Iron deficiency, cognition, mental health and fatigue in women of childbearing age: A systematic review. https://pubmed.ncbi.nlm.nih.gov/25191562/

Harvard T.H. Chan School of Public Health. Iron. https://nutritionsource.hsph.harvard.edu/iron/

Healthdirect Australia. How to meet your iron needs. https://www.healthdirect.gov.au/how-to-meet-your-iron-needs-infographic

Healthdirect Australia. Iron deficiency. https://www.healthdirect.gov.au/iron-deficiency

Kim, J., & Wessling-Resnick, M. (2014). Iron and mechanisms of emotional behavior. Journal of Nutritional Biochemistry, 25(11), 1101-1107. https://doi.org/10.1016/j.jnutbio.2014.07.003

Luo, J., Wang, X., Yuan, L., & Guo, L. (2021). Iron deficiency, a risk factor of thyroid disorders in reproductive-age and pregnant women: A systematic review and meta-analysis. https://pmc.ncbi.nlm.nih.gov/articles/PMC7947868/

National Institutes of Health, Office of Dietary Supplements. Iron: Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/

Nutrition Australia. (2021). Iron. https://nutritionaustralia.org/resources/iron/

Pivina, L., Semenova, Y., Doşa, M. D., Dauletyarova, M., & Bjørklund, G. (2019). Iron deficiency, cognitive functions, and neurobehavioral disorders in children. Journal of Molecular Neuroscience, 68(1), 1-10. https://doi.org/10.1007/s12031-019-01276-1

Rizvi, S., et al. (2025). Restless legs and iron deficiency: Unravelling the hidden link and current evidence. https://pmc.ncbi.nlm.nih.gov/articles/PMC12084866/

Sleep. (2025). Bringing iron to the brain for restless legs. https://academic.oup.com/sleep/article/48/7/zsaf128/8129076

U.S. Department of Agriculture. FoodData Central. https://fdc.nal.usda.gov/

Yin, R., Gao, Q., Fu, G., & Zhao, Q. (2024). The causal effect of iron status on risk of anxiety disorders: A two-sample Mendelian randomization study. PLOS ONE, 19(3), e0300143. https://doi.org/10.1371/journal.pone.0300143