Red blood cells (RBC), are the functional component of blood responsible for the transportation of gases and nutrients throughout the human body. Their unique shape and composition allow for these specialized cells to carry out their essential functions. The role of the erythrocyte is critical in investigating many disease processes in a variety of body systems. Their structure, function, physiology, preparation, microscopy, and clinical importance are the subject of this review article.
Red blood cells (RBCs), also referred to as red cells red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells, or erythrocytes are the most common type of blood cell and the vertebrate’s principal means of delivering oxygen (O2) to the body tissues—via blood flow through the circulatory system.[rx] RBCs take up oxygen in the lungs, or in fish the gills, and release it into tissues while squeezing through the body’s capillaries.
Red blood cells lack nuclei and have a biconcave shape.
The biconcave shape allows RBCs to bend and flow smoothly through the body’s capillaries. It also facilitates oxygen transport.
Red blood cells are considered cells, but they lack a nucleus, DNA, and organelles like the endoplasmic reticulum or mitochondria.
Red blood cells cannot divide or replicate like other bodily cells. They cannot independently synthesize proteins.
The blood’s red color is due to the spectral properties of the hemic iron ions in hemoglobin.
Each human red blood cell contains approximately 270 million hemoglobin biomolecules, each carrying four heme groups to which oxygen binds.
iron: A metallic chemical element with atomic number 26 and symbol Fe. Iron-containing enzymes and proteins, often containing heme prosthetic groups, participate in many biological oxidations and in transport.
hemoglobin: The iron-containing substance in RBCs that transports oxygen from the lungs to the rest of the body. It consists of a protein (globulin) and haem (a porphyrin ring with an atom of iron at its center).
Human erythrocytes or red blood cells (RBCs) are the primary cellular component of blood. They are involved in oxygen transport through the body and have features that distinguish them from every other type of human cell. Adult humans have roughly 20-30 trillion RBCs at any given time, comprising approximately one-quarter of the total number of human cells.
RBCs are disc-shaped with a flatter, concave center. This biconcave shape allows the cells to flow smoothly through the narrowest blood vessels. Gas exchange with tissues occurs in capillaries, tiny blood vessels that are only as wide as one cell. Many RBCs are wider than capillaries, but their shape provides the needed flexibility to squeeze through.
A typical human RBC has a disk diameter of 6–8 micrometers and a thickness of 2 micrometers, much smaller than most other human cells. These cells have an average volume of about 90 femtoliters (fL) with a surface area of about 136 square micrometers. They can swell up to a sphere shape containing 150 fL without bursting their cell membrane. When the shape does change, it inhibits their ability to carry oxygen or participate in gas exchange. This occurs in people with spherocytic (sphere-shaped) anemia or sickle-cell anemia.
Although RBCs are considered cells, they lack a nucleus, nuclear DNA, and most organelles, including the endoplasmic reticulum and mitochondria. RBCs therefore cannot divide or replicate like other labile cells of the body. They also lack the components to express genes and synthesize proteins. While most cells have chemotaxis ways to travel through the body, RBCs are carried through the body by blood flow and pressure alone.
Hemoglobin molecules are the most important component of RBCs. Hemoglobin is a specialized protein that contains a binding site for the transport of oxygen and other molecules. The RBCs’ distinctive red color is due to the spectral properties of the binding of hemic iron ions in hemoglobin. Each human red blood cell contains approximately 270 million of these hemoglobin biomolecules, each carrying four heme groups (individual proteins). Hemoglobin comprises about a third of the total RBC volume. This protein is responsible for the transport of more than 98% of the oxygen, while the rest travels as dissolved molecules through the plasma.
The primary functions of red blood cells (RBCs) include carrying oxygen to all parts of the body, binding to hemoglobin, and removing carbon dioxide.
Red blood cells contain hemoglobin, which contains four iron-binding heme groups.
Oxygen binds the heme groups of hemoglobin. Each hemoglobin molecule can bind four oxygen molecules.
The binding affinity of hemoglobin for oxygen is cooperative. It is increased by the oxygen saturation of the molecule. The binding of an initial oxygen molecule influences the shape of the other binding sites. This makes binding more favorable for additional oxygen molecules.
Each hemoglobin molecule contains four iron-binding heme groups which are the site of oxygen binding. Oxygen-bound hemoglobin is called oxyhemoglobin.
Red blood cells alter blood pH by catalyzing the reversible carbon dioxide to carbonic acid reaction through the enzyme carbonic anhydrase.
pH is also controlled by carbon dioxide binding to hemoglobin instead of being converted to carbonic acid.
carbonic anhydrase: The enzyme found in RBCs that catalyzes the reaction between carbonic acid and carbon dioxide and water.
cooperative binding: In binding in which multiple molecules can potentially bind to multiple binding sites when a first molecule is bound to a binding site, the same molecule is favored for the rest of the binding sites through increased binding affinity.
Red blood cells (RBCs) perform a number of human respiratory and cardiovascular system functions. Most of these functions are attributed to hemoglobin content. The main RBC functions are facilitating gas exchange and regulating blood pH.
Heme: This is a diagram of the molecular structure of heme.
RBCs facilitate gas exchange through a protein called hemoglobin. The word hemoglobin comes from “hemo” meaning blood and “globin” meaning protein. Hemoglobin is a quaternary structure protein consisting of many smaller tertiary structure proteins composed of amino acid polypeptide chains. Each hemoglobin molecule contains four iron-binding heme groups, which are the site of oxygen (O2) binding. Oxygen-bound hemoglobin is called oxyhemoglobin.
The binding of oxygen is a cooperative process. Hemoglobin bound oxygen causes a gradual increase in oxygen-binding affinity until all binding sites on the hemoglobin molecule are filled. As a result, the oxygen-binding curve of hemoglobin (also called the oxygen saturation or dissociation curve) is sigmoidal, or S-shaped, as opposed to the normal hyperbolic curve associated with noncooperative binding. This curve shows the saturation of oxygen bound to hemoglobin compared to the partial pressure of oxygen (concentration) in blood.
Oxygen saturation curve: Due to cooperative binding, the oxygen saturation curve is S-shaped.
RBCs control blood pH by changing the form of carbon dioxide within the blood. Carbon dioxide is associated with blood acidity. That’s because most carbon dioxide travels through the blood as a bicarbonate ion, which is the dissociated form of carbonic acid in the solution. The respiratory system regulates blood pH by changing the rate at which carbon dioxide is exhaled from the body, which involves the RBC’s molecular activity. RBCs alter blood pH in a few different ways.
Quaternary structure: hemoglobin: Hemoglobin is a globular protein composed of four polypeptide subunits (two alpha chains, in blue, and two beta-pleated sheets, in red). The heme groups are the green structures nestled among the alpha and beta.
RBCs secrete the enzyme carbonic anhydrase, which catalyzes the conversion of carbon dioxide and water to carbonic acid. This dissociates in solution into bicarbonate and hydrogen ions, the driving force of pH in the blood. This reaction is reversible by the same enzyme. Carbonic anhydrase also removes water from carbonic acid to turn it back into carbon dioxide and water. This process is essential so carbon dioxide can exist as a gas during a gas exchange in the alveolar capillaries. As carbon dioxide is converted from its dissolved acid form and exhaled through the lungs, blood pH becomes less acidic. This reaction can occur without the presence of RBCs or carbonic anhydrase but at a much slower rate. With the catalyst activity of carbonic anhydrase, this reaction is one of the fastest in the human body.
Hemoglobin can also bind to carbon dioxide, which creates carbamino-hemoglobin. When carbon dioxide binds to hemoglobin, it doesn’t exist in the form of carbonic acid, which makes the blood less acidic and increases blood pH. However, because of allosteric effects on the hemoglobin molecule, the binding of carbon dioxide decreases the amount of oxygen bound for a given partial pressure of oxygen. This decrease in hemoglobin’s affinity for oxygen by the binding of carbon dioxide is known as the Bohr effect, which results in a rightward shift to the O2-saturation curve. Conversely, when the carbon dioxide levels in the blood decrease (i.e., in the lung capillaries), carbon dioxide and hydrogen ions are released from hemoglobin, increasing the oxygen affinity of the protein. A reduction in the total binding capacity of hemoglobin to oxygen (i.e. shifting the curve down, not just to the right) due to reduced pH is called the Haldane effect.
Red blood cell count
A red blood cell (RBC) count is a blood test that tells you how many red blood cells you have.
Red blood cells contain a substance called hemoglobin, which transports oxygen around the body. The amount of oxygen that’s delivered to your body’s tissues depends on the number of red blood cells you have and how well they work. An RBC count is usually carried out as part of a full blood cell (FBC) count. Women usually have a lower RBC count than men, and the level of red blood cells tends to decrease with age.
A normal RBC count would be
men – 4.7 to 6.1 million cells per microlitre (cells/mcL)
women – 4.2 to 5.4 million cells/mcL
The results of an RBC count can be used to help diagnose blood-related conditions, such as iron deficiency anemia (where there are fewer red blood cells than normal).
RBC Life Cycle
Human erythrocytes are produced through a process called erythropoiesis. They take about seven days to mature.
After about 100-120 days, RBCs are removed from circulation through a process called eryptosis.
Erythropoiesis is the process by which human erythrocytes are produced. It is triggered by erythropoietin, a kidney hormone produced during hypoxia.
Erythropoiesis takes place in the bone marrow, where hemopoietic stem cells differentiate and eventually shed their nuclei to become reticulocytes. Iron, vitamin B12, and folic acid are required for hemoglobin synthesis and normal RBC maturation.
Reticulocytes mature into normal, functional RBCs after 24 hours in the bloodstream.
Following eryptosis, the liver breaks down old hemoglobin into biliverdin and iron. The iron is taken back to the bone marrow for reuse by transferrins, while biliverdin is broken down into bilirubin and excreted through the digestive system bile.
erythropoietin: A hormone produced by the kidneys in response to hypoxia, which stimulates erythropoiesis.
bilirubin: A bile pigment that arises when biliverdin is separated from the iron of old hemoglobin molecules in the liver. Bilirubin becomes part of bile salts in the digestive system and is excreted, while the iron content is reused.
Human erythrocytes are produced through a process called erythropoiesis, developing from committed stem cells to mature erythrocytes in about seven days. When matured, these cells circulate in the blood for about 100 to 120 days, performing their normal function of molecule transport. At the end of their lifespan, they degrade and are removed from circulation.
Scanning electron micrograph of blood cells: Shown on the left, the erythrocyte, or red blood cell, has a round, donut-like shape.
Erythropoiesis is the process in which new erythrocytes are produced, which takes about seven days. Erythrocytes are continuously produced in the red bone marrow of large bones at a rate of about 2 million cells per second in a healthy adult. Erythrocytes differentiate from erythropoietic bone marrow cells, a type of hemopoietic stem cell found in the bone marrow. Unlike mature RBCs, bone marrow cells contain a nucleus. In the embryo, the liver is the main site of red blood cell production and bears similar types of stem cells at this stage of development.
Erythropoiesis can be stimulated by the hormone erythropoietin, which is synthesized by the kidney in response to hypoxia (systemic oxygen deficiency). In the last stages of development, immature RBCs absorb iron, Vitamin B12, and folic acid. These dietary nutrients are necessary for the proper synthesis of hemoglobin (iron) and normal RBC development (B12 and folic acid). Deficiency of any of these nutrients may cause anemia, a condition in which there aren’t enough fully functional RBCs carrying oxygen in the bloodstream. Just before and after leaving the bone marrow, the developing cells are known as reticulocytes. These immature RBCs have shed their nuclei following initial differentiation. After 24 hours in the bloodstream, reticulocytes mature into functional RBCs.
Eryptosis, a form of apoptosis (programmed cell death), is the aging and death of mature RBCs. As an RBC age, it undergoes changes in its plasma membrane that make it susceptible to selective recognition by macrophages and subsequent phagocytosis in the reticuloendothelial system (spleen, liver, and bone marrow). This process removes old and defective cells and continually purges the blood. Eryptosis normally occurs at the same rate as erythropoiesis, keeping the total circulating red blood cell count in a state of equilibrium. Many diseases that involve damage to RBCs (hemolytic anemias, sepsis, malaria, pernicious or nutritional anemias) or normal cellular processes that cause cellular damage (oxidative stress) may increase the rate of eryptosis. Conversely, erythropoietin and nitric oxide (a vasodilator) will inhibit eryptosis.
Following eryptosis, the hemoglobin content within the RBC is broken down and recirculated throughout the body. The heme components of hemoglobin are broken down into iron ions and a green bile pigment called biliverdin. The biliverdin is reduced to the yellow bile pigment bilirubin, which is released into the plasma and recirculated to the liver, then bound to albumin and stored in the gallbladder. The bilirubin is excreted through the digestive system in the form of bile, while some of the iron is released into the plasma to be recirculated back into the bone marrow by a carrier protein called transferrin. This iron is then reused for erythropoiesis, but additional dietary iron is needed to support healthy RBC life cycles.
Red blood cells (RBCs), also called erythrocytes, are cells that circulate in the blood and carry oxygen throughout the body. The RBC count totals the number of red blood cells that are present in your sample of blood. It is one test among several that is included in a complete blood count (CBC) and is often used in the general evaluation of a person’s health.
Blood is made up of a few different types of cells suspended in fluid called plasma. In addition to RBCs, there are white blood cells (WBCs) and platelets. These cells are produced in the bone marrow and are released into the bloodstream as they mature. RBCs typically make up about 40% of the blood volume. RBCs contain hemoglobin, a protein that binds to oxygen and enables RBCs to carry oxygen from the lungs to the tissues and organs of the body. RBCs also help transport a small portion of carbon dioxide, a waste product of cell metabolism, from those tissues and organs back to the lungs, where it is expelled.
The typical lifespan of an RBC is 120 days. Thus the bone marrow must continually produce new RBCs to replace those that age and degrade or are lost through bleeding. A number of conditions can affect RBC production and some conditions may result in significant bleeding. Other disorders may affect the lifespan of RBCs in circulation, especially if the RBCs are deformed due to an inherited or acquired defect or abnormality. These conditions may lead to a rise or drop in the RBC count. Changes in the RBC count usually mirror changes in other RBC tests, including the hematocrit and hemoglobin level.
If RBCs are lost or destroyed faster than they can be replaced if bone marrow production is disrupted, or if the RBCs produced do not function normally, or do not contain enough hemoglobin, then you may develop anemia, which affects the amount of oxygen reaching tissues.
If too many RBCs are produced and released, then you can develop polycythemia. This can cause thicker blood, decreased blood flow, and related problems, such as headache, dizziness, problems with vision, and even excessive clotting or heart attack.
How is the test used?
A red blood cell (RBC) count is typically ordered as part of a complete blood count (CBC) and may be used as part of a health checkup to screen for a variety of conditions. This test may also be used to help diagnose and/or monitor a number of diseases that affect the production or lifespan of red blood cells.
When is it ordered?
An RBC count is ordered as a part of the complete blood count (CBC), often as part of a routine physical or as part of a pre-surgical workup. A CBC may be ordered when you have signs and symptoms suggesting a disease that might affect red blood cell production. Some common signs and symptoms associated with anemia that generally lead to a healthcare practitioner ordering a CBC are:
Weakness or fatigue
Lack of energy
Some signs and symptoms that may appear with a high RBC count include
A CBC may also be performed on a regular basis to monitor people who have been diagnosed with conditions such as
Bone marrow disorders
Cancer, like chemotherapy or radiation therapy, often decreases bone marrow production of all the blood cells
What does the test result mean?
Since an RBC count is performed as part of a complete blood count (CBC), results from other components are taken into consideration. A rise or drop in the RBC count must be interpreted in conjunction with other tests, such as hemoglobin, hematocrit, reticulocyte count, and/or red blood cell indices.
The following table summarizes what results may mean.
Examples of Causes of Low Result
Examples of Causes of High Result
Red Blood Cell Count (RBC)
Men: 4.5-5.9 x 106/microliter
Women: 4.1-5.1 x 106 microliter
Men: 4.5-5.9 x 1012/L
Women: 4.1-5.1 x 1012/L
Known as anemia
Acute or chronic bleeding
RBC destruction (e.g., hemolytic anemia, etc.)
Nutritional deficiency (e.g., iron deficiency, vitamin B12 or folate deficiency)
Bone marrow disorders or damage
Chronic inflammatory disease
Chronic kidney disease
Known as polycythemia
Lung (pulmonary) disease
Kidney or another tumor that produces excess erythropoietin
Living at high altitude
Genetic causes (altered oxygen sensing, abnormality in hemoglobin oxygen release)
Polycythemia vera—a rare disease
from Henry’s Clinical Diagnosis and Management by Laboratory Methods. 22nd ed.
McPherson R, Pincus M, eds. Philadelphia, PA: Elsevier Saunders; 2011.
Note: Conventional Units are typically used for reporting results in U.S. labs;
SI Units are used to report lab results outside of the U.S.
Some causes of a low RBC count (anemia) include
Trauma that leads to loss of blood
Conditions that cause red blood cells to be destroyed, such as hemolytic anemia caused by autoimmunity or defects in the red cell itself; the defects could be a hemoglobinopathy (e.g., sickle cell anemia), thalassemia, an abnormality in the RBC membrane (e.g., hereditary spherocytosis), or enzyme defect (e.g., G6PD deficiency).
Sudden (acute) or chronic bleeding from the digestive tract (e.g., ulcers, polyps, colon cancer) or other sites, such as the bladder or uterus (in women, heavy menstrual bleeding, for example)
Nutritional deficiency such as iron deficiency or vitamin B12 or folate deficiency
Bone marrow damage (e.g., toxin, radiation or chemotherapy, infection, drugs)
Bone marrow disorders such as leukemia, multiple myeloma, myelodysplastic syndrome, or lymphoma or other cancers that spread to the bone marrow
Chronic inflammatory disease or condition
Kidney failure—severe and chronic kidney diseases lead to decreased production of erythropoietin, a hormone produced by the kidneys that promote RBC production by the bone marrow.
Some causes of a high RBC count (polycythemia) include
Dehydration – as the volume of fluid in the blood drops, the count of RBCs per volume of fluid artificially rises.
Lung (pulmonary) disease – if someone is unable to breathe in and absorb sufficient oxygen, the body tries to compensate by producing more red blood cells.
Congenital heart disease – with this condition, the heart is not able to pump blood efficiently, resulting in a decreased amount of oxygen getting to tissues. The body tries to compensate by producing more red blood cells.
Kidney tumor that produces excess erythropoietin
Genetic causes (altered oxygen sensing, abnormality in hemoglobin oxygen release)
Polycythemia vera—a rare disease in which the body produces too many RBCs
My RBC count is slightly out of range. What does this mean?
Your RBC count is interpreted by your healthcare practitioner within the context of other tests that you have had done as well as other factors, such as your medical history. A single result that is slightly high or low may or may not have medical significance. There are several reasons why a test result may differ on different days and why it may fall outside a designated reference range.
Biological variability (different results in the same person at different times): If you have the same test done on several different occasions, there’s a good chance that one result will fall outside a reference range even though you are in good health. For biological reasons, your values can vary from day today.
Individual variability (differences in results between different people): References ranges are usually established by collecting results from a large population and determining from the data an expected average result and expected differences from that average (standard deviation). There are individuals who are healthy but whose tests results, which are normal for them, do not always fall within the expected range of the overall population.
A test value that falls outside of the established reference range supplied by the laboratory may mean nothing significant. Generally, this is the case when the test value is only slightly higher or lower than the reference range and this is why a healthcare practitioner may repeat a test on you and why they may look at results from prior times when you had the same test performed.
However, a result outside the range may indicate a problem and warrant further investigation. Your healthcare provider will consider your medical history, physical exam, and other relevant factors to determine whether a result that falls outside of the reference range means something significant for you.
If my RBC Count is out of range, what other tests might be done?
An RBC count can be used to detect a problem with red blood cell production and/or lifespan, but it cannot determine the underlying cause. In addition to the full CBC, some other tests may be performed at the same time or as a follow-up to help establish a diagnosis. Examples include:
Blood smear—a laboratory professional examines the blood under the microscope to confirm results of a CBC and/or to look abnormal blood cells
Reticulocyte count—determines the number of young (immature) red blood cells
Iron studies—iron is important in the production of red blood cells
Vitamin B12 and folate levels—these vitamins are also important for red blood cell production
In more severe conditions, a bone marrow aspiration and biopsy—usually done by a pathologist to help detect abnormalities in the bone marrow and determine the cause of low or high blood cell counts or abnormal blood cells
How treatable are abnormal red blood cell counts?
First, a healthcare practitioner must determine the cause of someone’s abnormal RBC count so the appropriate treatment can be prescribed. For some anemias, treatment may include a dietary supplement or a change in diet to include nutritional foods. In some instances, it may only require a change in the person’s current medication. For more severe cases, treatment may involve transfusion with blood from a donor. For some, prescribing a drug to stimulate red cell production in the bone marrow may be required, especially for people who have received chemotherapy or radiation treatments.
How to Increase Your Red Blood Cell Count
Anemia and red blood cell count
Are you feeling weak or fatigued? You may be experiencing symptoms of anemia. Anemia occurs when your red blood cell (RBC) count is low. If your RBC count is low, your body has to work harder to deliver oxygen throughout your body.
RBCs are the most common cells in human blood. The body produces millions each day. RBCs are produced in the bone marrow and circulate around the body for 120 days. Then, they go to the liver, which destroys them and recycles their cellular components.
Anemia can put you at risk for a number of complications, so it’s important to get your RBC levels back on track as soon as possible.
Keep reading to learn how to increase your RBCs at home, how your doctor can help, and more.
5 nutrients that increase red blood cell counts
Eating foods rich in these five nutrients can help you improve your red blood cell levels.
Eating an iron-rich diet can increase your body’s production of RBCs. Iron-rich foods include:
red meat, such as beef
organ meat, such as kidney and liver
dark, leafy, green vegetables, such as spinach and kale
dried fruits, such as prunes and raisins
Adding certain B vitamins to your diet can also be beneficial. Foods high in vitamin B-9 (folic acid) include:
dark, leafy, green vegetables, such as spinach and kale
Foods high in vitamin B-12 include:
red meat, such as beef
dairy products, such as milk and cheese
Copper intake doesn’t directly result in RBC production, but it can help your RBCs access the iron they need to replicate. Foods high in copper include:
Vitamin A (retinol) also supports RBC production in this manner. Foods rich in vitamin A include:
dark, leafy green vegetables, such as spinach and kale
fruits, such as watermelon, grapefruit, and cantaloupe
8 supplements that increase red blood cell counts
If you aren’t getting enough key nutrients through your diet, you may want to talk to your doctor about taking supplements. Certain supplements can help increase your RBC production or support related processes in your body.
Some supplements can interact with medications that you may be taking, so be sure to get your doctor’s approval before adding them to your regimen.
Never take more than the recommended dosage found on the product’s label.
Supplements your doctor may suggest include
Iron – Iron deficiency commonly causes low RBC production. Women need about 18 milligrams (mg) per day, whereas men only need 8 mg per day.
Vitamin C – This vitamin may help your body better absorb iron. The average adult needs about 500 mg per day.
Copper – There may also be a link between low RBC production and copper deficiency. Women need 18 mg per day, and men need 8 mg per day. However, your daily copper requirement depends on a variety of factors, including sex, age, and body weight. Be sure to consult your doctor or a dietitian to understand how much you need.
Vitamin A (retinol) – Women need 700 micrograms (mcg) per day. For men, the recommendation increases to 900 mcg.
Vitamin B-12 – Most people who are 14 years and older need 2.4 mcg of this vitamin per day. If you’re pregnant, the recommended dosage raises to 2.6 mcg. If you’re breastfeeding, it jumps to 2.8 mcg.
Vitamin B-9 (folic acid) – The average person needs between 100 and 250 mcg per day. If you regularly menstruate, it’s recommended that you take 400 mcg. Women who are pregnant need 600 mcg per day.
Vitamin B-6 – Women need about 1.5 mg of this nutrient each day, and men need about 1.7 mg.
Vitamin E – The average adult needs about 15 mg per day.
How to Increase the Absorption of Iron From Foods
Iron is an essential mineral your body needs to function properly.
Thus, it’s vitally important to consume adequate amounts of it in your daily diet. Interestingly, the foods you eat influence not only how much iron you consume, but also how well it is absorbed into your body [rx].
Once it’s absorbed by your body, it’s used as a building block for hemoglobin, a protein found in red blood cells that helps shuttle oxygen around your body. Iron is also a component of myoglobin, an oxygen storage protein found in your muscles. This oxygen is used when you use your muscles.
The recommended intake range is 7–18 mg per day for the general population and up to 27 grams for pregnant women [rx].
Which Foods Contain It?
You may have heard that you can get iron from red meat, but there are many other foods that naturally contain iron.
In foods, iron is present in two forms: heme and non-heme.
Sources of Heme Iron
Heme iron is found in animal foods that contain hemoglobin, such as meat, fish and poultry.
Heme iron is the best form of iron, as up to 40% of it is readily absorbed by your body [rx].
Good food sources of heme iron include:
Fish such as halibut, haddock, perch, salmon or tuna
Shellfish such as clams, oysters and mussels
Red meats and organ meats like liver are particularly good sources.
Sources of Non-Heme Iron
Non-heme iron primarily comes from plant sources and is present in grains, vegetables and fortified foods.
This is the form added to foods enriched or fortified with iron, as well as many supplements.
It’s estimated that 85–90% of total iron intake comes from the non-heme form, while 10–15% comes from the heme form [rx].
In terms of its bioavailability, non-heme iron is absorbed much less efficiently than heme iron.
Good sources of non-heme iron include:
Fortified cereals, rice, wheat and oats
Dark green leafy vegetables like spinach and kale
Dried fruits like raisins and apricots
Beans like lentils and soybeans
Heme iron is found in animal foods, while non-heme iron comes from plant sources. The heme form is better absorbed by your body than the non-heme form
Certain Populations May Be at Risk of Deficiency
Iron deficiency is the most common cause of anemia, which affects a billion people worldwide [rx].
A person who is iron deficient may have various symptoms, including fatigue, dizziness, headaches, sensitivity to cold, and shortness of breath when doing simple tasks.
Moreover, iron deficiency can result in poorer attention span and mental function. In fact, being deficient during early childhood has been linked to lower IQs [rx]
Children, adolescents, and women of reproductive age, particularly during pregnancy, are most at risk of iron deficiency. This is because their intake doesn’t meet their body’s high demand for it [rx]
Additionally, it’s commonly thought that vegetarians and vegans are more prone to iron deficiency. But, interestingly, studies have shown that vegetarian and vegan diets contain just as much iron, if not more, than diets containing meat
However, although vegetarians may consume as much iron as non-vegetarians, a review found that they are still at greater risk of deficiency [rx]
This is because they consume mainly non-heme iron, which is not absorbed as well as the heme form in animal products.
It’s generally recommended that vegetarians multiply their recommended iron intake by 1.8 times to compensate for the reduced absorption [rx].