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Why You Should Be Concerned if You See Blood in Your Stool

blood in your stool

Story at-a-glance -

  • Colorectal cancer is the third most common cancer in the U.S., affecting 1.3 million people in 2015, and it is the second leading cause of cancer-related deaths
  • Some cancers have early signs, but not colorectal cancer; a common screening involves testing for nearly invisible blood in the stool to find a cancerous growth early, increasing the potential for better treatment options
  • Researchers have found trace amounts of blood in the stool increase your risk of premature death from all causes by 58 percent, which may be the result of inflammation leading to other diseases
  • Only 5 to 10 percent of cancers are related to genetics; making simple lifestyle changes with your diet and exercise, maintaining your weight and controlling belly fat may cut your risk of colorectal cancer in half

By Dr. Mercola

Colorectal cancer, which includes cancers of the colon and rectum, is the third most common cancer diagnosed in the U.S., and is the second leading cause of cancer related deaths.1 The condition affected 1.3 million people in 2015.2 Based on data from the National Cancer Institute, relative survival after five years is just over 64 percent.3

Your colon, also known as your large intestines, plays an important role in your overall health. Aside from removing liquid from stool and preparing it for elimination, your colon contains billions of bacteria essential for your optimal health. Early screening and detection increases your potential for survival as it allows for a greater number of treatment options.

It is uncommon for early colorectal cancers to have signs and symptoms.4 One of the simplest tests used to determine if there is an abnormality in the colon is a fecal occult blood test (FOBT) that detects hidden traces of blood in your stool. However, a recent study demonstrates this "invisible" blood may also be linked to a heightened risk of death from all causes.5

Occult Blood May Offer a Window Into Your Health

Even when blood is not visible to the naked eye in your stool, it can signal the presence of other potentially fatal health conditions other than colon cancer. Researchers found those who had trace amounts of blood in their stool had a 58 percent higher risk of premature death from a variety of causes.6

A standard test for colon cancer looks for blood in the stool, often associated with bleeding in the colorectal area. However, these surprising results indicate bleeding in the colon may also be a sign of other conditions not normally associated with internal bleeding. The researchers looked at medical records of more than 130,000 people living in Scotland who had an FOBT between 2000 and 2016.7

During this time, 2 percent of the participants, about 2,700, had a positive test.8 As expected, those whose test came back positive were seven times more likely to eventually die of colon cancer than those who did not have blood in their stool. The more surprising result was the association of noncolorectal cancer mortality with those who also had a positive FOBT.

Although this was an observational study with no immediate link to causality, researchers speculated the presence of an inflammatory response may produce bleeding in the body.9 There is strong evidence to suggest many cancers, Alzheimer's disease and other chronic illnesses occur with chronic systemic inflammation, potentially linking the presence of occult fecal blood with other health conditions.

As noted by the authors,10 "factors predisposing to ill-health, such as obesity, sedentary behavior, smoking, alcohol dependence and a western diet, have been shown to be associated with systemic inflammation."

In an accompanying commentary,11 a professor from Stanford University School of Medicine speculates the FOBT may offer unique insights into your general health and, more importantly, is a predictor of life expectancy. The professor points out the current study confirms and expands on previous observations reporting a relationship between all-cause mortality and fecal blood. Occult blood may also provide you with a window into your health, beyond your colon and rectum.

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Other Reasons for Blood in Your Stool

The researchers found older age, increasing levels of deprivation, male gender and prescriptions for aspirin or other drugs boosting the risk of digestive tract bleeding, were associated with a positive test result. While FOBT testing for occult blood in the stool is commonly used to screen colon cancer, there are other reasons you may have visible or occult blood in your stool.

Finding blood in your stool can be frightening and while it may signal a serious problem, it doesn't always. For the most part, it means there's bleeding somewhere in your digestive tract, as the tube leading from your mouth to your rectum is completely separate from your other internal organs. Sometimes the blood may be bright red and appear on your toilet tissue and at other times bleeding happens higher in the digestive tract making the stool appear black and tarry. Possible causes include:12,13

Diverticular disease

These are small pouches projecting from the colon wall, which don't usually cause problems but sometimes bleed or become infected.


These are swollen veins in the lowest part of your rectum and anus and are sometimes called piles.14 Hemorrhoids are one of the most common causes of rectal bleeding as the vein is sometimes stretched so thin they get irritated, causing them to crack and bleed. While rarely dangerous and usually clear up in a couple of weeks, you may want to consult with your physician to ensure it's not a more serious condition.

Anal fissure

This is a small cut or tear in the tissue lining the anus, similar in appearance to cracks on chapped lips or a paper cut. Fissures may happen when passing large hard stool.


This is a condition in which your blood vessels are fragile and may lead to bleeding.

Peptic ulcers

Peptic ulcers may occur in the stomach or upper end of the small intestines. Caused by an infection with helicobacter pylori, they may cause open bleeding areas. As the bleeding occurs higher in the digestive tract, it causes your stool to appear black. Long term use of anti-inflammatory drugs such as aspirin, ibuprofen or naproxen may also cause ulcers.

Polyps or cancer

Polyps are benign growths, which sometimes become cancerous. Both polyps and colorectal cancer may cause bleeding not seen with the naked eye.


This is an infection in your stomach, often presenting with runny stools, containing mucus and traces of blood. It can result from a virus, bacteria or food poisoning, and while the main symptom is diarrhea it can also include vomiting, stomach pain and dehydration.

Inflammatory bowel disease (IBD)

The two main forms of IBD are Crohn's disease and ulcerative colitis. The condition is not the same as irritable bowel syndrome and is a chronic condition responsible for inflaming the intestinal walls, often resulting in diarrhea, pain and weight loss.

Symptoms and Screening for Colorectal Cancer

Frequently symptoms of colorectal cancer appear only after the cancer has grown or spread. This is why a simple screening before symptoms may find problems earlier when it's often easier to treat. While there are some symptoms indicating colorectal cancer, diagnosis requires further testing. Symptoms may include:15

  • A change in bowel habits, such as diarrhea, constipation or narrowing of the stool, lasting more than a few days
  • Blood in the stool is either dark or bright red
  • A feeling of fullness, not relieved by having a bowel movement
  • Cramping or abdominal pain
  • Weakness, fatigue and unintended weight loss

Screening tests are done in individuals who have no symptoms, but several tests may be used to check for cancerous growth when symptoms are present.16 Stool tests are less invasive and easier to be done, while visual exams of the structure of the colon and rectum will look for abnormal areas and will be done using either a scope with a tiny video camera on the end or with special imaging. A stool DNA test may be done after a positive FOBT to look for mutated sections of DNA coming from cancer or polyps cells that are released into the stool.

Visual exams look at the inside of the colon and rectum for abnormal areas. This testing requires more preparation and has some associated risks not found with stool-based exams. During a colonoscopy the entire length of the colon and rectum is viewed with a colonoscope, a flexible tube about the width of your finger with a light and small video camera on the end. A flexible sigmoidoscopy is similar, but only the lower end of the rectum and colon are viewed.

During a CT colonography or virtual colonoscopy, a CT scan is used to take many pictures as it rotates around you on a table. A special computer program allows your physician to see 2-dimensional and 3-dimensional views of the colon and may be useful for individuals who can't have a more invasive test, as it can be done fairly quickly and sedation is not needed. However, while not invasive like a colonoscopy, bowel preparation is still needed and if suspicious areas are seen, a colonoscopy will still be used to remove them or explore further.

There are significant risks associated with colonoscopies that you need to be aware of. To learn more, see "The Pros and Cons of Colonoscopies." Importantly, most sigmoidoscopes and colonoscopies are not properly sterilized between patients, which can have serious risks.

An estimated 80 percent of endoscopes are cleaned using Cidex (glutaraldehyde), which does NOT properly sterilize these tools, potentially allowing for the transfer of infectious material from one patient into another. If you need to get a colonoscopy or flexible sigmoidoscopy, it is imperative that you contact the office before the procedure to make sure they are decontaminating the scope properly with peracetic acid and not Cidex.

Blood tests are often used to help monitor or diagnose cancer. A complete blood count will show if you have anemia, which is common in those who have been bleeding for a long time. Liver enzymes may be tested as spread to the liver is common with colorectal cancer. Blood tests for tumor markers may be done as they suggest possible colorectal cancer but are not used for screening or diagnosis alone. Tumor markers are more commonly used to monitor treatment or as an early warning for colorectal cancer recurrence.17

Help Protect Yourself Against Colon Cancer

According to a study published in Pharmaceutical Research18 only 5 to 10 percent of cancers are due to genetic defects and the rest are likely linked to environment and lifestyle factors. This means, while colorectal cancer is a leading cause of cancer deaths in the U.S., it is often preventable. The researchers estimated19 nearly 35 percent of all cancer-related deaths may be due to diet, another 30 percent to tobacco use, 20 percent to infection and the rest to other environmental factors, including exposure to radiation, stress, physical activity levels and environmental pollution.

I would add that mitochondrial dysfunction is at the heart of all cancers — often referred to as the metabolic theory of cancer — and all of these lifestyle and environmental factors affect your mitochondrial function. According to the American Institute for Cancer Research, one-third of most common U.S. cancer cases are preventable through a healthy diet, being physically active and maintaining a healthy weight.20

The percentage of colorectal cancers that may be preventable using these lifestyle factors rises to 50 percent. In my previous article, "How to Help Protect Against Colon Cancer," I discuss the top nine lifestyle choices to consider making today in order to reduce your risk of this deadly disease.

Even after treatment for colon cancer, genetic mutations can survive in stem cells and reappear to trigger a relapse.21 In initial studies, researchers found low levels of retinoic acid (a metabolite of retinol or vitamin A) in mice with colon cancer.22 When given extra doses, the disease progression slowed. A study from Switzerland found a protein in the gut, identified as HOXA5, plays a major role in restricting the number of stem cells and the cells making them.23

Colon cancer stem cells use a biological mechanism to block HOXA5. Researchers found retinoid, compounds related to vitamin A, can reactivate the protein, thereby slowing the progression of colon cancer.24 Many think eating carrots and sweet potatoes increases their levels of vitamin A. However, there are two different kinds, bioavailable retinoid from animals and carotenoids found in plant-based foods.

You may be able to lower your risk of colon cancer by drinking soursop tea. A study published in 2015 states that annomurucin E, a substance found in soursop leaves, may help lower the risk of colon cancer.25

Only the retinoid version is absorbable, while your body converts plant-based carotenoids into retinoid. Some factors may prevent this process, such as alcohol, certain foods and medications, low-fat diet and medical conditions preventing fat absorption. Your best sources of healthy vitamin A are eggs from organic pastured chickens and whole raw milk and cream, butter and cheeses from organic grass fed cows.

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