Symptoms of low iron. What iron deficiency actually feels like
One of the most common nutritional deficiencies in the UK, and one of the most commonly missed.
Iron deficiency is the most widespread nutritional deficiency worldwide, and in the UK it is particularly common among women of reproductive age, pregnant women, and people eating plant-based diets. Yet because the symptoms develop gradually and overlap with everyday feelings of tiredness and stress, it often goes unrecognised for months or years.
This article covers what iron does in the body, what the symptoms of low iron actually feel like, why some groups are more vulnerable, the best dietary sources, what supplementation looks like, and why some people's bodies absorb iron less efficiently than others even when their diet is good.
"Iron deficiency is the most common nutritional deficiency in the world. In the UK, many of the people affected have no idea."
What iron actually does
Iron's most critical role is in the production of haemoglobin, the protein in red blood cells that carries oxygen from the lungs to every cell in the body. Without adequate iron, the body cannot produce enough functional red blood cells, and oxygen delivery throughout the body is impaired. This is the mechanism behind most of the symptoms associated with low iron.
Iron is also essential for myoglobin, the protein that stores and transports oxygen within muscle tissue, and for the production of ATP, the molecule cells use for energy. Beyond oxygen transport, iron plays roles in immune function, cognitive performance, and the regulation of body temperature. The brain is particularly sensitive to iron status. Iron is required for the synthesis of dopamine and serotonin, which helps explain the mood and concentration effects associated with low iron.
Symptoms of iron deficiency. What low levels actually feel like
Iron deficiency exists on a spectrum. In the early stages, when iron stores (measured as ferritin) are depleted but haemoglobin levels are still normal, symptoms are subtle. As deficiency progresses into iron deficiency anaemia, symptoms become more pronounced. The most consistently reported signs are:
😔
Most common
Persistent fatigue and exhaustion
The most common and most debilitating symptom. Because iron is central to oxygen delivery, low iron means cells, particularly in working muscles and the brain, receive less oxygen than they need. The result is a fatigue that does not resolve with rest and often worsens throughout the day.
💨
Breathing
Shortness of breath
Feeling breathless during activities that would not normally cause it, such as climbing stairs, walking briskly, or light exercise, is a classic sign of iron deficiency. The body compensates for reduced oxygen delivery by increasing breathing rate.
👁️
Appearance
Pale skin and pale inner eyelids
Haemoglobin gives blood its red colour. When haemoglobin is low, skin and the mucous membranes, including the inner lower eyelids, lose their normal pink tone. Pulling down the lower eyelid and looking at the inner rim is one of the simple checks a GP will often use.
💓
Heart
Heart palpitations
The heart works harder to compensate for reduced oxygen delivery, which can cause a noticeable awareness of the heartbeat, particularly during activity or at rest when lying down.
🤕
Head
Headaches and dizziness
Reduced oxygen delivery to the brain causes headaches and lightheadedness. This is particularly common when standing up quickly.
🥶
Circulation
Cold hands and feet
Poor circulation caused by low red blood cell production leads to reduced blood flow to the extremities, resulting in persistently cold hands and feet even in warm conditions.
💅
Physical
Brittle nails and hair loss
Iron is required for healthy cell production including nail and hair cells. Brittle, ridged, or spoon-shaped nails (koilonychia) and increased hair shedding are associated with iron deficiency, though they tend to appear later in the progression.
🧠
Cognitive
Difficulty concentrating and brain fog
Iron is required for the synthesis of neurotransmitters including dopamine. Low iron is consistently associated with reduced concentration, slower processing, and the kind of mental sluggishness often described as brain fog.
🦵
Sleep
Restless legs syndrome
Low iron is strongly associated with restless legs syndrome, an uncomfortable urge to move the legs particularly at night. The mechanism involves iron's role in dopamine regulation in the brain.
🧊
Cravings
Unusual food cravings (pica)
Some people with iron deficiency develop cravings for non-food items such as ice, clay, or soil. This is known as pica and is a recognised, if less common, sign of significant deficiency.
When to speak to your GP
The only way to confirm iron deficiency is a blood test. A full blood count (FBC) measures haemoglobin and red blood cell levels, while a ferritin test measures iron stores. If you are experiencing persistent fatigue, breathlessness, frequent headaches, or several of the symptoms above, speak with your GP about testing. Iron deficiency can be a sign of an underlying issue — including blood loss — that warrants investigation.
Who is most at risk
Iron deficiency is more common in certain groups:
♀️
Most at risk
Women of reproductive age
Monthly blood loss through menstruation depletes iron stores. Women with heavy periods are particularly at risk.
🤰
Increased need
Pregnant women
Iron requirements increase significantly during pregnancy to support the growing foetus and placenta.
🌱
Diet
Plant-based and vegetarian diets
Plant foods contain non-haem iron, which is less efficiently absorbed than the haem iron in meat and fish.
🏃
Exercise
Endurance athletes
Intense exercise increases iron loss through sweat, urine, and foot-strike haemolysis, the destruction of red blood cells with each foot strike while running.
🫁
Health conditions
Gastrointestinal conditions
Coeliac disease, Crohn's disease, and inflammatory bowel disease all reduce iron absorption in the gut.
👴
Age
Older adults
Older adults may have reduced dietary intake and absorption efficiency, making iron deficiency more common with age.
The best dietary sources of iron
There are two types of dietary iron: haem iron, found in animal products, and non-haem iron, found in plant foods. Haem iron is absorbed significantly more efficiently, at around 15 to 35 percent absorption compared to 2 to 20 percent for non-haem iron. This is why iron deficiency is more common among people eating predominantly plant-based diets.
Approximate iron content per 100g serving
Liver (beef, cooked)6.5mg
Pumpkin seeds8.8mg
Lentils (cooked)3.3mg
Spinach (cooked)3.6mg
Tofu (firm)2.7mg
Beef (lean, cooked)2.7mg
Sardines (tinned)2.9mg
Fortified breakfast cerealvaries — check label
UK recommended daily intake: 8.7mg (men and post-menopausal women) | 14.8mg (women aged 19–50)
Vitamin C significantly improves iron absorption
Eating vitamin C-rich foods alongside plant-based iron sources substantially increases non-haem iron absorption. A glass of orange juice, a serving of peppers, or a squeeze of lemon over spinach makes a meaningful practical difference. Tannins in tea and coffee reduce iron absorption. Avoiding these with meals that are your main iron source is worth doing.
Supplementation — what to know
If a blood test confirms iron deficiency, your GP will typically recommend iron supplementation. Ferrous sulfate is the most commonly prescribed form and is effective, though it causes digestive side effects in some people. Ferrous gluconate and ferrous fumarate are gentler alternatives with similar efficacy. Iron bisglycinate (also called chelated iron) is available over the counter and is generally well tolerated with fewer digestive side effects, though it is more expensive.
Iron supplements are best taken on an empty stomach for maximum absorption, though this can increase the likelihood of nausea. Taking with a small amount of food is a reasonable compromise. Taking iron with vitamin C improves absorption. Calcium, dairy products, and antacids all reduce iron absorption and should be separated from iron supplementation by at least two hours.
Do not self-supplement with iron without a confirmed deficiency. Unlike water-soluble vitamins, excess iron is not easily excreted and can cause harm at high doses. A blood test first is the right approach.
Why some people absorb iron less efficiently — the genetics dimension
For most people with low iron, the cause is straightforward: dietary intake that does not meet requirements, or blood loss that is not being compensated. But genetics plays a meaningful role in iron absorption efficiency, which helps explain why some people consistently struggle with iron status despite a diet that should be sufficient.
The TMPRSS6 gene encodes a protein that regulates hepcidin, the hormone that controls how much iron the gut absorbs. Variants in TMPRSS6 are associated with lower iron absorption and higher rates of iron deficiency. The HFE gene influences how the body regulates iron stores. Variants in genes encoding transferrin, the protein that transports iron in the blood, affect how efficiently iron is moved from the gut into circulation. For people eating plant-based diets, variants affecting the absorption of non-haem iron are particularly relevant, since non-haem iron absorption is more variable and more influenced by genetic factors than haem iron absorption.
In the Boone app
Boone analyses genetic variants relevant to iron absorption and transport, showing you whether your body is likely to absorb iron efficiently or whether you may need to pay more deliberate attention to your dietary sources and food combinations. Combined with the food log tracking your dietary iron intake and the micro nutrition scores showing what your iron picture means for your Energy and Immunity, it gives you a personal picture rather than a generic one.
What to do if you think your iron is low
The most important first step is a blood test. Ask your GP for a full blood count and a ferritin test. Ferritin measures iron stores and is a more sensitive early indicator of deficiency than haemoglobin alone.
In the meantime, focus on iron-rich dietary sources. If you eat meat, include red meat and liver periodically. If you eat fish, sardines and other oily fish are useful sources. If you eat a predominantly plant-based diet, prioritise lentils, tofu, pumpkin seeds, and fortified foods, always alongside vitamin C-rich foods to improve absorption. Reduce tea and coffee with meals if iron is a known concern.
If deficiency is confirmed, supplement with the form your GP recommends or with iron bisglycinate if you are self-managing and find other forms cause digestive discomfort. Retest after 8 to 16 weeks to assess whether levels have improved.
"For most people, low iron is a diagnosable and fixable problem. A blood test, targeted dietary changes, and supplementation where needed covers the majority of cases. Understanding your genetic absorption profile tells you how deliberate you need to be."
The earliest signs are often subtle. Persistent tiredness despite adequate sleep, reduced exercise tolerance, and difficulty concentrating. These appear when iron stores (ferritin) are depleted but before haemoglobin levels fall significantly. As deficiency progresses, more noticeable symptoms appear including pale skin, shortness of breath, heart palpitations, and cold hands and feet. The only way to confirm iron deficiency is a blood test measuring ferritin and haemoglobin.
Low iron is associated with mood changes including low mood and anxiety. Iron is required for the synthesis of dopamine and serotonin, neurotransmitters that regulate mood. Reduced oxygen delivery to the brain also contributes to mental fatigue that can present similarly to low mood. Addressing iron deficiency often improves mood, though it is not a treatment for clinical anxiety or depression.
Haemoglobin levels typically normalise within 4 to 8 weeks of effective supplementation. Rebuilding iron stores (ferritin) takes longer, usually 3 to 6 months. This is why a follow-up blood test after 8 to 16 weeks is important to assess progress, and why supplementation is usually continued for several months after haemoglobin normalises.
Plant foods contain non-haem iron, which is absorbed less efficiently than the haem iron found in meat and fish. Non-haem iron absorption ranges from 2 to 20 percent, compared to 15 to 35 percent for haem iron. However, eating vitamin C-rich foods alongside plant-based iron sources significantly improves absorption. People eating plant-based diets can meet their iron needs but typically need to be more deliberate about food choices and combinations.
Yes. Variants in genes including TMPRSS6, HFE, and transferrin-related genes influence how efficiently the body absorbs and transports iron. These genetic differences help explain why some people consistently have lower iron levels than expected despite adequate dietary intake, and why iron needs are not the same for everyone.
No. Iron supplementation without confirmed deficiency is not recommended. Unlike water-soluble vitamins, excess iron is not easily excreted and can cause harm at high doses over time. A blood test measuring ferritin and haemoglobin is the right first step before supplementing. If you are experiencing symptoms of iron deficiency, speak with your GP about testing.
Understand your personal iron picture.
Boone analyses your genetic profile for iron absorption and transport variants and connects those insights to your real diet. It shows you your dietary iron sources, your micro nutrition scores across Energy and Immunity, and personalised food recommendations that address your specific gaps.
Download the Boone app and discover what your nutritional picture looks like.
