Understanding Anemia And How It Relates To Colon Cancer

Anemia is a fairly common term that describes a deficiency of red blood cells or hemoglobin, an iron-rich protein. However, people may misunderstand anemia as a diagnosis of a condition rather than a symptom indicative of many diseases. Therefore, a doctor may not focus on the anemia itself but will focus on the problem causing the anemia.

For example, anemia may be a symptom indicating an iron deficiency, lead poisoning, and, yes, colon cancer. This article will provide an all-inclusive look at anemia, its symptoms, and how it relates to colon cancer.

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What are the symptoms of anemia?

The job of the red blood cells and hemoglobin is to receive oxygen from the lungs and bring it to the tissues throughout the body. A deficiency of red blood cells or hemoglobin means that the blood cannot carry enough oxygen.

When there are not enough red blood cells to carry the required amount of oxygen throughout the body, the body’s tissues may experience a lack of oxygen. This can lead to symptoms such as:

  • Weakness

  • Fast or irregular heartbeat

  • Headache

  • Pounding or a "whooshing" sound in your ears

  • Cold hands or feet

  • Chest pain

  • Dizziness

  • Fatigue

  • Pale skin

  • Jaundice (yellowish skin, eyes, and mouth)

What is jaundice?

Red blood cells generally have a life expectancy of about 120 days. When the red blood cells wear out, the liver and spleen take them out of circulation and destroy them so that the body can reuse some of their nutrients. This process produces an orange-yellow pigment called bilirubin.

At the same time, the bone marrow continually produces more red blood cells to replace the ones that are no longer viable and destroyed.

Jaundice occurs when bilirubin builds up in the body, leading to a yellowing of the skin and the whites of the eyes. There are many potential causes of jaundice. One of these is a type of anemia known as hemolytic anemia, in which the liver and spleen destroy red blood cells too quickly before their normal lifespan is over.

Types of anemia by cause

Anemia simply means a lack of red blood cells. There are many different potential causes of anemia.

Iron deficiency anemia

Iron deficiency is the most common type of anemia. Iron is needed to create healthy red blood cells because it’s an important component of hemoglobin, the protein that carries oxygen. If you don’t have enough iron, then you’ll end up with a low red blood cell count. In most cases, a doctor can quickly pinpoint and treat conditions causing this kind of anemia. 

If you have iron deficiency anemia, it’s important to ensure that your diet contains the right amount of iron. The recommended daily amount differs based on age and sex, with women needing more iron than men (due to menstruation, which causes women to lose iron every month). In addition, a woman who is pregnant or breastfeeding needs extra iron. If you’re not getting enough, then you may need to.  

Some people take in enough iron, but their digestive tract cannot absorb it well enough. This can be caused by diseases that impair the ability of the intestines to absorb nutrients, such as celiac disease.

Iron deficiency anemia can also be caused by blood loss. In this case, even though you’re taking in a normal amount of iron, you’re losing it too quickly and are unable to replace it. This can indicate a blood loss issue, such as fibroids, excessively heavy menstruation, or blood loss in the digestive tract.

Vitamin B12 deficiency anemia

As with iron-deficiency anemia, it's essential to pay attention to the recommended daily amount of vitamin B12 that you should be taking in. However, other risk factors can contribute to a vitamin B12 deficiency:

  • Your body is unable to absorb vitamin B12 because of the intrinsic factor.

  • You drink too much alcohol daily, preventing your body from absorbing vitamin B12.

  • You take certain medicines that can make it more difficult to absorb vitamin B12.

  • You may have a medical condition that can contribute to vitamin B12 deficiency.

Hemolytic anemia

This anemia occurs when your body destroys many old or defective red blood cells. This process, called hemolysis, will leave the body with a lower red blood count than required. More severe conditions cause this type of anemia, such as:

  • Autoimmune conditions like rheumatoid arthritis or inflammatory bowel disease

  • Bone marrow failure

  • Infections

  • Side-effects of some medicines

  • Inherited blood disorders like sickle cell anemia

The severity of hemolytic anemia will determine the severity of the treatment needed. Physicians may not have to treat some people with mild hemolytic anemia. In contrast, others with severe anemia need treatment to avoid symptoms, such as irregular heart rhythms, a larger-than-normal heart, or heart failure.

Treatments for severe hemolytic anemia include:

  • Medicines

  • Blood transfusions

  • Blood or bone marrow transplants

  • Surgery to remove the spleen

Aplastic anemia

This type of anemia occurs because the bone marrow cannot produce enough red blood cells. In this case, the bone marrow cannot produce enough red blood cells because the body attacks the bone marrow stem cells, damaging them.

Treatments for this type of anemia can range from medicines to blood and bone marrow transplants.

Anemia and other symptoms that can indicate colon cancer

Symptoms rarely present themselves in the early stages of colon cancer. Even then, the signs that do appear will depend on where the tumor is growing in the intestine. Let's look at the many symptoms that may indicate colon cancer.


Intestinal bleeding may occur in patients with colon cancer, and because of this, anemia may occur. As discussed before, when blood loss happens, there is a loss of red blood cells. If too many red blood cells are lost, the patient may develop anemia, which could cause symptoms like paleness of the skin, fatigue, dizziness, and increased heart rate. 

Also, a growing tumor can cause systemic inflammation or activation of the immune system. This can block the formation of red blood cells, resulting in anemia.

Rectal bleeding

A person experiencing rectal bleeding may see some blood in the toilet or on the toilet paper after using the bathroom. The blood may be bright red or darker, depending on how far the bleeding is from the rectum. 

If the bleeding occurs closer to the rectum, such as in the left colon or the rectum itself, the blood will be bright red. The further bleeding occurs from the rectum, such as in the right colon, the darker the blood. This is because the digestive system acts on the blood and changes its color.

Blood in the stool

As the stool (also known as feces or poop) passes through the intestines, it will pass through any bleeding that may occur there. When the stool leaves the body, the blood may be visible on or in the stool. Blood in the stool is not always visible in patients with colon cancer because the bleeding may occur at very low levels. 

Abdominal pain and bloating

Most people will experience digestive issues at some point in their lives, including stomach bloating, cramps, or pain. When this occurs, a potential cause is usually apparent, such as gas, indigestion, fluid retention, and menstruation. However, patients with colon cancer experience these symptoms frequently and without an obvious reason.

Changes in bowel movements

Again, most people will experience changes in their bowel movements once in a while due to diet, medications, or other reasons. Patients with colon cancer generally experience bowel movement problems quite regularly. Tumors can partially block the colon, making bowel movements uncomfortable and unusual.

Bowel movement abnormalities that colon cancer patients may experience include:

  • Diarrhea, constipation, or alternating between these

  • Bowels that don't feel empty even after you’ve just gone to the bathroom

  • Stools that are narrower than usual 

  • A change in the frequency of bowel movements

Symptoms tend to develop faster if the obstruction is in the left colon rather than the right.

Nausea and vomiting

While partial obstructions of the intestines from a tumor can cause unusual bowel movements, a complete blockage can cause nausea and vomiting. The total obstruction of the bowel prevents liquids, solids, or gasses from passing through. As these backups, it causes persistent nausea and vomiting.

Nausea and vomiting can also result from treatments used for colon cancer, such as chemotherapy. In this case, dehydration and a lack of nutrition can make it harder for your body to heal, so it's best to keep hydrated and eat during the treatment process, even if you may not feel like it. Eating small meals every two hours, consisting of bland foods, may help alleviate nausea. 

Loss of appetite and unexplained weight loss

Abdominal pain, bloating, and nausea can lead to a loss of appetite, while diarrhea and vomiting can contribute to unexplained weight loss. These factors may lead to a lack of nutrition, contributing to anemia. All of this together often causes the colon cancer patient to feel weak and tired. 

Why does colon cancer cause anemia?

When a tumor grows in the colon, it will often bleed because it has a network of blood vessels. In the early stages of cancer, the tumor’s blood vessel network is fragile and will tend to bleed slightly. As cancer grows, it will invade the normal tissue surrounding it, extending into the blood vessels of that normal tissue and causing additional bleeding.

However, this internal bleeding will most likely cause you to notice rectal bleeding before it becomes severe enough to cause anemia. As the tumor grows and spreads, the bleeding may become more severe, which can lead to anemia.

What stage of colon cancer causes anemia?

In a study published in the World Journal of Surgical Oncology,¹ the researchers found that the more advanced the colon cancer, the more patients tested positive for preoperative anemia. The study tested two groups of colon cancer patients, including both men and women. One group had earlier-stage cancers, which had not yet spread from the colon to other parts of the body. The other group had more advanced cancers, which had spread more widely.

The study found that the more advanced cancer, the more likely the patients were to have anemia. In the group of patients in the earlier stages of colon cancer, 29% tested positive for anemia, and 4% had severe anemia. In the group of patients in a more advanced stage of colon cancer, 46% tested positive for anemia, and 17% had severe anemia.  

Anemia of chronic disease (AOCD)

Diseases that cause inflammation can lead to anemia, a process known as inflammation anemia or anemia of chronic disease (AOCD). This occurs because inflammation can interfere with the process of making new red blood cells. Many conditions can cause this, including:

  • Rheumatoid arthritis

  • Lupus

  • Cancer


  • Tuberculosis

  • Inflammatory bowel disease (IBD), Crohn's disease, or ulcerative colitis

  • Diabetes

Inflammation is a process of immune system activation. The inflammation signals the immune cells to fight foreign invaders to help heal an infection. It can be triggered by the presence of any abnormal proteins that the body doesn’t recognize as belonging to your own cells.

Cancer cells often contain abnormal proteins because they have developed mutations in their genes — this can activate the immune system. In addition, cancer cells often produce various proteins that act on the immune system. These may trigger an inflammatory response while protecting the cancer cells from being destroyed by the immune system.

So colon cancer can lead to symptoms of anemia not only due to blood loss but also due to inflammation.

Early detection of colon cancer

Adults aged 45 to 75 should undergo regular screening for colon cancer. The screening will help find colon cancer earlier when it’s easier to treat, rather than later. For people with risk factors for colon cancer, such as Crohn's disease, ulcerative colitis, another inflammatory bowel disease, or a strong family history of colorectal cancer or colon polyps, it may be beneficial to begin screening at an earlier age. 

There are risk factors that increase the risk of getting colon cancer. Some of these include:

  • Excessive alcohol use

  • Cigarette smoking

  • Obesity

  • Sedentary lifestyle

  • Poor diet

It’s best to address these risk factors to reduce the chances of colon cancer. If you have any of these risk factors, it’s even more important to complete your recommended colon cancer screenings.

The most common and convenient method of testing is stool tests. These tests require the patient to collect a stool sample using a kit and return it to the doctor or lab, where it’s tested for blood. If blood is found, then you’ll need additional testing for colon cancer. There are several different ways to do this.

gFOBT test

The method of testing for the gFOBT stool test is using a chemical to detect heme. This is a component of a protein called hemoglobin, which is found in red blood cells. This type of screening reduces the risk of death due to colon cancer if it’s performed every one to two years in people aged 50 to 80. 

The downside to this type of screening is that you must avoid certain foods before taking the test. Heme is also found in certain foods (such as red meat), which can lead to a false positive test.

FIT test

The FIT stool test uses antibodies to detect the hemoglobin protein. This type of testing is more sensitive than the gFOBT stool test and can detect more colon cancers. Similarly to the gFOBT test, it should be performed every one to two years. The test does not require dietary restrictions.

FIT-DNA test

This screening process detects hemoglobin and DNA biomarkers from the cells in the lining of the colon and rectum that collect in the stool. This type of screening is even more sensitive and can detect more colon cancers than the gFOBT and the FIT tests. 

However, the FIT-DNA test is more likely to produce false-positive results than the other tests. The false positives could lead to unnecessary additional testing. 

If this is the method chosen for your screening, you should get this test every three years.


When a stool test returns with a positive result, additional testing is needed to confirm whether colon cancer may be present. At that point, a colonoscopy is necessary. Colonoscopies can also be performed as the primary screening test without doing stool testing first.

A colonoscopy is a more invasive test that uses an instrument called a colonoscope. This device is a long flexible tube with a light and a camera on the end, which is inserted through the anus to allow the physician to see inside the colon. Air is pumped into the colon to inflate it so the physician can see the lining more clearly. 

The colonoscope also allows the insertion of specially designed instruments for removing tissue. The doctor will remove any abnormal growths and may perform biopsies of areas that are suspected of being precancerous or cancerous. The tissue samples are sent to a laboratory, where they’re analyzed.

There is a small risk when the doctor performs the colonoscopy. While performing the test, tears or holes can sometimes occur in the wall of the colon. There can also be bleeding from the sites where the tissue was removed, and some people may have a bad reaction to the sedative medication. However, colonoscopy is considered a very safe procedure, and the risk of serious complications is very low. 

Medical experts recommend you get this test every ten years, as long as no precancerous tissue was found. If there were any concerning changes, you might need to return sooner.

Virtual colonoscopy

This type of testing involves a CT scan, which uses X-rays to take images of the colon and rectum from outside the body. Then a computer assembles these pictures into 3D images, allowing doctors to check for concerning growths or abnormalities. If these are detected, you will need a colonoscopy to remove and test them.

This screening process may not be widely available or covered by insurance. Also, the process causes exposure to a small amount of radiation. 

If this testing is used, it’s recommended every five years.

When to see a doctor

It's time to see a physician if you have symptoms that could indicate colon cancer, such as abdominal bloating or pain, or diarrhea, which starts suddenly or last for a longer time than usual. Likewise, if you have symptoms that could indicate anemia, you should also make an appointment with a doctor. They can pinpoint the actual cause of the anemia and treat it appropriately.

When you turn 45, talk to your doctor about setting up a colon cancer screening test. If you’re at increased risk due to your family history or any medical conditions, see a doctor before you are 45.

The lowdown

It's dangerous to ignore symptoms of anemia, like persistent weakness or fatigue, a rapid heartbeat, pale skin, or jaundice. Ignoring these symptoms could mean that the organs in your body don’t get the oxygen they need to function correctly. It’s important to determine the cause of the anemia and treat it.

Remember, anemia is a sign that something is wrong. It could indicate many conditions, from benign, such as an iron deficiency, to malignant, such as colon cancer. Pay attention when you experience symptoms of anemia and visit the doctor for more information and treatment.

  1. Anemia can predict the prognosis of colorectal cancer in the pre-operative stage: A retrospective analysis (2021)

Other sources:

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