6 mins read

Red Blood Cell (RBC)

Red blood cells are vital for the transport of oxygen around the body, but if their numbers fluctuate it can lead to some debilitating symptoms.

Author: Leanne Edermaniger

April 30, 2024

Reviewed by: Dr Thom Phillips

In this article:

What are Red Blood Cells?

Red blood cells, also called erythrocytes, are important functional components of blood and have pivotal roles in transporting oxygen, carbon dioxide, and nutrients around the body.

Red blood cells have a distinctive size and shape that enable them to carry out their functions. For example, the cells are biconcave discs which helps to maximise their surface area and increase their oxygen-carrying capacity. Plus, the shape also provides some flexibility as the cell travels through the narrow blood vessels.

The characteristic red colour is because of their haemoglobin content, the iron-containing protein responsible for binding to and transporting oxygen around the body and removing carbon dioxide.

What are the functions of red blood cells?

  • Deliver oxygen to the cells and tissues to help generate energy
  • Transport carbon dioxide from the tissues to the lungs for removal from the body[1]

How long do red blood cells live?

Healthy red blood cells live for an average of 120 days before being processed by special immune cells called macrophages[2].

What is a red blood cell count?

Red blood cells have important roles in the body and can also be a good indicator of health and disease.

To find out how many red blood cells you have, you may have a red blood cell count[3]. The test tells you how many red cells are present in a litre of blood and may indicate if there is any presence of disease or illness.

What is a Good Red Blood Cell Count?

The normal range for a red blood cell count can differ between the testing laboratory, but women tend to have a lower red blood cell count than men, and the number of red blood cells seems to decline with increasing age[4].

Generally, a healthy range is:

  • 4.0 to 5.2 x 1012/L for women
  • 4.5 to 5.9 x 1012’L for men

At Forth, our data shows that 89% of people have a red blood cell count that falls within a healthy range.

What Happens if Your RBC is Too Low?

Anaemia is a common condition that causes a low number of red blood cells or reduced haemoglobin levels.

A low red cell count can indicate deficiencies in vitamin B6, B12, or B9 (folate). Vitamin B12 and folate deficiency are the world’s most common causes of megaloblastic anaemia. This type of anaemia causes unusually large red blood cells and a reduced number which lessens their oxygen-carrying capacity[5].

Symptoms of vitamin B12 or folate deficiency

  • Fatigue
  • Weakness
  • Increased heart rate
  • Shortness of breath
  • Pale skin
  • Bruising or bleeding easily
  • Sore tongue
  • Upset stomach
  • Weight loss
  • Diarrhoea
  • Constipation
  • Tingling or numbness in your fingers and toes
  • Mood changes
  • Depression
  • Memory issues[6]

Other causes of low red blood cells

Vitamin B12 and folate deficiencies are not the only causes of a low red blood cell count, others include:

  • Iron deficiency: Iron is an important component of haemoglobin, the protein responsible for transporting oxygen around the body. Iron deficiency limits the production of haemoglobin and the subsequent production of red blood cells, resulting in anaemia.
  • Chronic disease: Long-term illnesses, such as chronic kidney disease, rheumatoid arthritis, and cancer can all cause low levels of red blood cells.
  • Malnutrition: If you do not eat the recommended intake of some nutrients, such as iron, it can impact the production of red blood cells.

How do you fix a low red blood cell count?

In some cases, it may be necessary to seek the advice of a doctor to increase your red blood cell levels. For example, you may need:

  • Medication to treat an underlying condition, such as an autoimmune disease.
  • You may need hormone treatment to help stimulate or increase the production of red blood cells, called erythropoietin.
  • A blood transfusion if your medication isn’t working.

However, you can make some simple lifestyle changes to support your body to produce a healthy number of red blood cells.

To make healthy red blood cells, some specific nutrients are required. So, it is useful to make sure you are eating foods that contain nutrients, such as iron, vitamin B12, and folate.

The following table lists the types of foods you should be including to help support the development of red blood cells.

Iron Vitamin B12 Vitamin B9
Lean, red meat Lean meat Dark green, leafy vegetables
Poultry Poultry Legumes and beans
Green, leafy vegetables Eggs Nuts
Lentils  Milk and milk products Wholegrains
Tofu  Shellfish e.g., oysters and clams Seeds
Shellfish e.g., oysters Fish  Fruit 

You may need to supplement your intake of some of these nutrients if they are found to be a cause of anaemia. A doctor may also prescribe medication to treat the underlying cause. For example, if anaemia is caused by iron deficiency, you may be prescribed iron tablets.

You can also help to support your red blood cell levels by limiting your alcohol intake. Increased alcohol consumption can lead to vitamin B12 and B9 deficiency, and increase the risk of developing megaloblastic anaemia[8].

Finally, exercise is important for all aspects of health and some research shows that it can promote a younger red blood cell population with improved functioning[9]. Further research shows that activities, such as jogging, can raise haemoglobin levels[10]. Exercise in general, increases blood flow to the muscles, delivering oxygen to the cells that need it, ready for energy production.

What Happens if Your RBC is Too High?

It is also possible to have a high number of red blood cells which may be caused by:

  • Congenital heart disease
  • Smoking
  • Dehydration
  • Low blood oxygen levels
  • Scarring on your lungs called pulmonary fibrosis
  • Sleep apnoea[11]
  • Living at high altitudes
  • Genetic mutations
  • Chronic obstructive pulmonary disease (COPD)

The use of performance-enhancing drugs, such as anabolic steroids, also increases the number of red blood cells[12]. Although illegal, blood doping improves the athlete’s performance by artificially increasing the individual’s oxygen-carrying capacity. However, blood doping is linked to serious health risks and can impair rather than improve performance[13].

A high concentration of red blood cells is referred to as erythrocytosis or polycythaemia. It increases the thickness of blood, making it more difficult to flow through your blood vessels.

Symptoms of a high red blood cell count

Some people who have erythrocytosis do not experience any symptoms, but if they do they are often related to sluggish blood flow, like:

  • Blurred vision
  • Headaches
  • Tiredness
  • High blood pressure
  • Dizziness
  • Tummy pain
  • Confusion
  • Gout
  • Itchy skin
  • Bleeding issues such as nosebleeds and bruising[14]

How do you fix a high red blood cell count?

For many people, erythrocytosis is a mild condition which doesn’t cause any side effects, while for others it may require further investigation and even medical treatment, either to treat the condition itself or any underlying conditions or complications. For example, people who experience itchy skin may need treatments to help deal with the effects.

Because a high red blood cell count is associated with an increased risk of blood clots, there are several things you may be able to do to help, including:

  • Losing weight if you are overweight or obese
  • Quitting smoking
  • Reducing your intake of red meat
  • Drinking more water throughout the day
  • Avoiding diuretics such as caffeine and alcohol

How to Check Your Red Blood Cell Count?

Testing your red blood cells can give you a unique insight into your wider health.

Checking your red blood cell count at home couldn’t be easier with our Ultimate Health Check.

The test measures 47 biomarkers to assess all key aspects of your health, pinpointing specific areas of your lifestyle that may need improvement to help you better support your overall health and wellbeing.

Written by Leanne Edermaniger

Based in the UK, Leanne specialises in writing about health, medicine, nutrition, and fitness.

She has over 5 years of experience in writing about health and lifestyle and has a BSc (hons) Biomedical Science and an MSc Science, Communication and Society.

- Health scores calculated


Article references

  1. Bizjak, D.A. et al. (2020) ‘Does endurance training improve red blood cell ageing and hemorheology in moderate-trained healthy individuals?’, Journal of Sport and Health Science, 9(6), pp. 595–603. doi:10.1016/j.jshs.2019.02.002.

  2. Sepriadi, Jannah, K. and Eldawaty (2020) ‘The effect of jogging exercise to improve haemoglobin levels’, Journal of Physics: Conference Series, 1481(1), p. 012028. doi:10.1088/1742-6596/1481/1/012028.

  3. Sawka, M. N., Joyner, M. J., Miles, D. S., Robertson, R. J., Spriet, L. L., & Young, A. J. (1996). American College of Sports Medicine position stand. The use of blood doping as an ergogenic aid. Medicine and science in sports and exercise, 28(6), i–viii.

This article was written by Leanne Edermaniger

This information has been medically reviewed by Dr Thom Phillips

Thom works in NHS general practice and has a decade of experience working in both male and female elite sport. He has a background in exercise physiology and has published research into fatigue biomarkers.

Dr Thom Phillips

Dr Thom Phillips

Head of Clinical Services