Haemoglobin
| Clinical | Optimal | |
|---|---|---|
| Male | 130 - 180 g/L | 130–170 g/L |
| Female | 115 - 165 g/L | 120–150 g/L |
What is Haemoglobin?
Haemoglobin (Hb) is the iron-containing protein inside every red blood cell that actually carries oxygen. Each red blood cell contains around 270 million haemoglobin molecules, and each molecule can carry up to four oxygen molecules — making it extraordinarily efficient at its job.
When haemoglobin picks up oxygen in your lungs, it turns bright red (which is why oxygenated blood appears red). When it releases oxygen to your tissues, it becomes darker — hence the bluer appearance of deoxygenated veins.
Your haemoglobin concentration tells you how much oxygen your blood can carry. It is arguably the most important number in a full blood count because it directly determines whether your body is getting enough oxygen to function optimally.
Why Haemoglobin Matters for Your Health
Haemoglobin is the cornerstone marker for diagnosing anaemia — a condition that affects approximately 1.6 billion people worldwide. Even mildly low haemoglobin can cause noticeable fatigue, reduced exercise tolerance, and difficulty concentrating.
For energy and performance, haemoglobin is king. Athletes obsess over it because even small changes affect endurance and recovery. But it matters just as much for everyday energy — getting through your day, concentrating at work, and having the vitality to exercise and enjoy life.
From a longevity perspective, chronic anaemia places strain on the heart (which must pump harder to compensate for reduced oxygen delivery) and is associated with cognitive decline in older adults. Maintaining optimal haemoglobin is a fundamental pillar of healthy ageing.
Haemoglobin& Your Wearable Data
Haemoglobin is the iron-containing protein in red blood cells that carries oxygen from your lungs to your tissues. It is one of the most performance-relevant biomarkers and has a direct relationship with wearable fitness metrics. Your VO2 max estimate is fundamentally dependent on haemoglobin concentration: each gram of haemoglobin carries approximately 1.34 mL of oxygen, so even small changes in haemoglobin affect aerobic capacity.
Your wearable's exercise heart rate data reflects haemoglobin status in real time. Low haemoglobin forces the heart to beat faster to deliver adequate oxygen, visible as elevated heart rates at given exercise intensities. If your wearable shows a gradual increase in exercise heart rates alongside declining VO2 max and increased perceived effort, anaemia should be investigated.
Endurance athletes frequently develop "sports anaemia" — a dilutional pseudoanaemia where plasma volume expansion from training lowers haemoglobin concentration despite normal or increased total haemoglobin mass. Wearable data showing excellent fitness metrics (high VO2 max, low resting heart rate, good recovery) alongside mildly low haemoglobin may indicate this benign adaptation rather than true anaemia.
What High Haemoglobin May Suggest
High haemoglobin means your blood is carrying more oxygen than usual per unit volume. While this might sound beneficial, it makes the blood thicker and harder for the heart to pump, increasing the risk of blood clots.
Common causes include dehydration (the most frequent reason for a mildly high result), smoking (the body compensates for carbon monoxide exposure by making more haemoglobin), chronic lung disease, sleep apnoea, living at altitude, and polycythaemia vera (a bone marrow disorder).
If your haemoglobin is mildly elevated, hydrate well and retest. If it is persistently high, your GP may investigate further. Symptoms of significantly high haemoglobin include headaches, dizziness, blurred vision, and a flushed complexion.
What Low Haemoglobin May Suggest
Low haemoglobin confirms anaemia — your blood cannot carry as much oxygen as your body needs. The severity of symptoms generally correlates with how low the haemoglobin has dropped and how quickly.
Iron deficiency is the most common cause in the UK, followed by B12 or folate deficiency, chronic disease, blood loss, and less commonly, bone marrow problems. Women of reproductive age are at higher risk due to menstrual blood loss.
Symptoms include persistent tiredness that rest does not fix, breathlessness on climbing stairs or mild exertion, pale skin and pale inner eyelids, dizziness, cold extremities, heart palpitations, and difficulty concentrating. Severe anaemia can cause chest pain and should be treated urgently.
How to Optimise Your Haemoglobin
Food
Prioritise iron-rich foods: lean red meat (the most absorbable haem iron), liver, sardines, mussels, dark turkey meat, and for plant-based options, lentils, chickpeas, and spinach paired with vitamin C. Include B12 (meat, fish, eggs) and folate (leafy greens, legumes). Beetroot has traditionally been used to support blood health and contains nitrates that may enhance oxygen delivery.
Lifestyle
Investigate and address any source of chronic blood loss with your GP. Regular exercise at moderate intensity stimulates haemoglobin production. Ensure adequate sleep for optimal bone marrow function. Avoid excessive tea and coffee consumption with meals, as tannins reduce iron absorption. If haemoglobin is high, stop smoking (if applicable), stay well hydrated, and seek investigation for sleep apnoea if you snore heavily.
Supplements
For iron-deficiency anaemia, iron bisglycinate (20–25 mg elemental iron) with vitamin C is effective and well tolerated. Vitamin B12 (methylcobalamin, 1,000 mcg) if deficient. Folate (methylfolate, 400–800 mcg) if deficient. Do not supplement iron without confirming deficiency first, as excess iron can be harmful. Allow 8–12 weeks for haemoglobin to improve with supplementation.
When to Speak to Your GP
See your GP if haemoglobin is below 120 g/L in men or 110 g/L in women, or if you have symptoms of anaemia at any level. Urgent review is needed for haemoglobin below 80 g/L, as this may require hospital assessment. Also see your GP for persistently high haemoglobin (above 170 g/L in men or 150 g/L in women) without an obvious cause.
References
- WHO. Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity. Geneva: WHO; 2011. who.int
- NHS. Iron deficiency anaemia — Overview. Updated 2024. nhs.uk
- NICE. Anaemia — Iron deficiency. NICE guideline NG210. nice.org.uk
- Lancet. Kassebaum NJ, et al. A systematic analysis of global anemia burden from 1990 to 2010. Blood. 2014;123(5):615-624. pubmed.ncbi.nlm.nih.gov
- BMJ. Goddard AF, et al. Guidelines for the management of iron deficiency anaemia. Gut. 2011;60(10):1309-1316. pubmed.ncbi.nlm.nih.gov
Medical Disclaimer— This content is for general educational and informational purposes only. It does not constitute medical advice, diagnosis, or treatment. Omniwo Ltd is a wellness information service and is not a medical device, clinical laboratory, or regulated healthcare provider under MHRA guidelines. The “optimal ranges” presented on this page are based on published clinical guidelines (WHO, NICE, NHS) and peer-reviewed research; they represent functional wellness targets and may differ from standard laboratory reference ranges. Individual results should always be interpreted by a qualified healthcare professional (such as your GP) who understands your full medical history. Do not start, stop, or change any medication or supplement based solely on this information. If you are experiencing symptoms, seek medical attention promptly.