Red Blood Cell Count

Red blood cell (RBC) count measures how many red blood cells are circulating in your blood. RBCs carry oxygen to your brain, muscles, and organs so they can make energy and work well. The test is part of a full blood count (FBC) and helps spot when your body is making too few or too many RBCs.

Your RBC count influences how much oxygen your body can deliver with each heartbeat and breath.

• Too low can mean reduced oxygen delivery, leading to tiredness, brain fog, low mood, headaches, reduced fitness, and greater strain on the heart. Common causes include low iron, vitamin B12 or folate, copper deficiency (all of which are needed for the production of red blood cells), blood loss, or conditions that break down RBCs (1,2).
  

• Too high thickens the blood, which can slow flow and stress the heart and lungs. Triggers include dehydration, living or training at high altitude, smoking-related lung changes, sleep apnea, and certain hormone or performance drugs (1).
  

Because RBCs live for about a few months, tracking this marker over time helps you see how everyday habits add up and whether changes you make are truly moving the needle.

RBC count changes in response to nutrition, hydration, oxygen levels, and bone marrow activity. Common influences include:

• Iron, B12, and folate status: Low levels reduce red-cell production and oxygen-carrying capacity.

• Copper deficiency: Impairs iron transport and red-cell synthesis.

• Blood loss: Heavy menstrual bleeding, gastrointestinal bleeding, or frequent donation can lower counts.

• Dehydration: Concentrates the blood, temporarily raising RBC count.

• Altitude and hypoxia: Living or training at elevation increases red-cell production to improve oxygen delivery.

• Smoking: Carbon monoxide exposure from smoking reduces oxygen availability, prompting higher RBC production.

• Sleep apnoea: Intermittent oxygen drops overnight stimulate red-cell production.

• Endurance training: Long-distance running and intense aerobic exercise can lower iron and damage red cells through “foot-strike haemolysis.”

• Hormonal or performance-enhancing drugs: Certain anabolic agents increase red-cell production and blood viscosity.

Think of RBCs as “oxygen couriers.” Your goal is to give them the right building blocks, limit things that block those blocks, and tailor your routine to your current level.

If your RBC count tends to be low

• Eat “iron-smart.” Include heme iron most people absorb well (lean red meat, sardines, mussels, chicken thigh), and pair plant iron (beans, lentils, tofu, spinach, pumpkin seeds) with vitamin C foods like capsicum, citrus, berries, or tomatoes to boost absorption .

• Time tea and coffee. Drinking coffee or tea with meals can cut non-heme iron absorption by roughly 40% for coffee and 60% for tea. Leave about 1 hour between these drinks and iron-rich meals to reduce the effect .

• Fortify your recipes. Add vitamin C–rich sides to grain and legume dishes, use tomato-based sauces with beans, and cook acidic tomato or citrus–based recipes with iron-friendly pairings. Small shifts at most meals compound over months .

• Mind the other builders. Low vitamin B12, folate, vitamin B6, or copper can also reduce RBC production. Add foods like eggs, dairy or B12-fortified plant milks, leafy greens, legumes, avocado, nuts, seeds, and shellfish .

• Train smart if you are an endurance athlete. Heavy mileage can increase iron losses and “foot-strike” haemolysis. Rotate in low-impact cardio, use cushioned shoes, and periodise long runs around iron-rich meals to protect your stores .
  
  

If your RBC count tends to be high

• Hydrate on a schedule. Dehydration concentrates the blood and can push RBC count upward. Aim for steady fluids across the day, especially with heat exposure, sauna, or intense training .

• Cut smoke exposure. Tobacco smoke causes lung changes and low oxygen that drive the body to make more RBCs. Reducing or stopping smoking can help bring the count toward your personal baseline over time .

• Check your environment and habits. Recent high-altitude trips or living/training at elevation naturally raise RBCs. Values often drift back down after you return to lower altitude. Avoid unnecessary high-dose iron supplements unless you truly need them .

• Prioritise sleep quality. Snoring and poor sleep may signal overnight low oxygen, a known driver of higher RBC counts. Simple steps such as side-sleeping, nasal breathing practice, and weight management can support healthier oxygen levels over time.
  

Make it trackable

• Keep the same testing conditions as much as possible, for example time of day and hydration.

• Combine your RBC count with related markers (haemoglobin, haematocrit, ferritin, B12, folate) to see the full picture, and keep an eye on trends across months and years rather than one-off results.

1. MedlinePlus. Red Blood Cell (RBC) Count: MedlinePlus Medical Test. National Library of Medicine, 2024. Available from: https://medlineplus.gov/lab-tests/red-blood-cell-rbc-count/
   

2. MedlinePlus Medical Encyclopedia. RBC count. National Library of Medicine, reviewed 2024. Available from: https://medlineplus.gov/ency/article/003644.htm
   

3. Iron — Health Professional Fact Sheet. Office of Dietary Supplements, National Institutes of Health, updated 2024. Available from: https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/
   

4. Inhibition of food iron absorption by coffee and tea. American Journal of Clinical Nutrition. Available from: https://ajcn.nutrition.org/article/S0002-9165%2823%2915679-6/fulltext
   

5. Harvard T.H. Chan School of Public Health. Iron – The Nutrition Source. Updated 2024. Available from: https://nutritionsource.hsph.harvard.edu/iron/