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Selenium supplements protect against colon cancer

- and routine screening is not enough

Selenium supplements protect against colon cancerCancer in the colon and rectum is rather common. One in 20 Danes gets colon cancer at some point in life. Since 2014, the Danish Health Authority has recommended a screening program, offering middle-aged and older people a screening for colon cancer every other year. If the disease is discovered in its early stage, the chances of successful treatment increase. Supplementation with organic selenium yeast has been shown to lower the risk of colorectal cancer in the first place, and selenium even has a protective effect against other cancer forms, so the nutrient is an essential part of the prevention. The problem is that selenium deficiencies are so common as a result of our nutrient-depleted soil.

In the spring of 2018, a large number of Danes aged 50-74 years received a letter from the Danish Health Authority, offering a screening test for early signs of colon cancer. The test involves checking a stool sample for signs of invisible blood. If no signs of blood are found, the person will be offered a new test in 2020.
If it appears that there is blood in the stools, a colonoscopy of the colon and rectum is the next move. This will show if there is cancer or polyps (intestinal growths) that may develop into colon cancer.

Every year, 5,000 Danes are diagnosed with colorectal cancer

Most people are older than 50 years, and their risk of dying of their disease increases, as they grow older
Cancer in the colon, rectum, and appendix are categorized as colorectal cancer. In Europe, it is the second most common cause of cancer-related deaths.

Worries, discomfort, and false alarms

The pamphlet from the Danish Health Authority states that the test may have several negative effects. Even though there are signs of blood in the stool sample, it may stem from harmless things such as bleeding from a rupture or a hemorrhoid. Similarly, if no signs of blood are found in the stool sample, there can still be cancer in the colon or rectum, which means that the screening result gives a false sense of security. After all, it is only a small part of a stool sample that is analyzed.
There is also a risk of overtreatment and unnecessary fear, as far from all polyps develop into cancer. Add to that the fact that many do not like the thought of having to send in a sample of their own feces. Still, based on a collective assessment of pros and cons, the Danish Health Authority recommends the screening program.

Around 20 percent of those who are diagnosed with colon cancer will survive if they participate in the screening program. However, it is also important to get enough selenium, which prevents the disease from occurring in the first place. This fact is not addressed in the pamphlet from the Danish Health Authority.

Selenium is an essential nutrient, which helps lower the risk of colon cancer and liver cancer

Selenium supports around 30 different enzymes (also known as selenoproteins) that are unable to function without selenium. Selenoproteins are important for our energy turnover, metabolism (thyroid gland), immune defense, reproduction, and they also have important antioxidant functions that protect cells against oxidative stress and DNA damage.
High levels of selenium in the blood are associated with a reduced risk of colon cancer and liver cancer. This was demonstrated in a study from 2017, which was headed by Dr. David Hughes, from the Conway Institute at the University College in Dublin. Hughes and his team of scientists analyzed data from the so-called EPIC study, where around 500,000 people had submitted blood samples and provided detailed information about their diet and lifestyle.
Several hundred participants, who had been diagnosed with cancer of the colon and the liver, had their levels of selenoprotein P measured. This particular selenoprotein transports selenium in the body and serves as an antioxidant and a marker for the selenium status in blood. Their blood samples were then compared with blood samples from healthy participants.
Hughes and his team found that higher selenium levels in the blood, including levels of selenoprotein P, were associated with a significantly lower risk of colon cancer and liver cancer. According to Dr. Hughes, their study suggests that a higher selenium intake may be relevant for most people in Europe, because the selenium intake in this part of the world is suboptimal.

Selenium supplements protect against colon polyps and colon cancer

Colon polyps are rather common. A particular type of colon polyp called adenoma is linked to the development of colon cancer in around five per cent of cases, and it is therefore important to monitor these patients.
In an earlier study, an Italian researcher named Luigina Bonelli wanted to demonstrate the ability of selenium and other antioxidant to prevent recurrence of adenomas. Three hundred people took part in the study. All patients had undergone surgical removal of adenomas in their colon. The patients were divided in two groups. One group received a Danish selenium preparation with selenium yeast combined with zinc and four antioxidant vitamins. The other group got placebo. Neither the researchers nor the patients knew who got what. After five years of treatment, the double-blind, placebo-controlled trial showed that the patients in the selenium group had a 50% lower incidence of malignant polyps compared with those in the placebo group, which meant that they had a far lower risk of developing colon cancer.

Long-term effect of selenium supplementation

Dr. Bonelli continued to monitor the two patient groups. About 15 years after the first study, the patients in the group that took selenium and antioxidants still had 41% lower recurrence of adenomas compared with the placebo group.
It is the first study to show that supplements of selenium and other antioxidants have a persistent and statistically significant ability to lower the risk of colorectal cancer.
Science does not know exactly how the specific nutrients affect the polyps, but it is a fact that antioxidants generally protect cells against oxidative stress caused by free radicals. Free radicals are highly aggressive molecules that are generated in the body. The free radical load is heavily increased by stress, poisoning, smoking, inflammation, overweight, ageing processes, and excess iron, which we get from e.g. read meat. Selenium has several anti-cancer properties.

Proper cancer prevention requires an adequate intake of selenium to saturate the many selenium-dependent compounds (selenoproteins) and their many functions. Selenoproteins work by

  • Serving as powerful antioxidants that protect cells against free radicals
  • Repairing DNA damage
  • Neutralizing environmental toxins such as mercury
  • Inhibiting blood vessel formation (angiogenesis) in tumors
  • Helping diseased cells self-destruct (apoptosis)
  • Contributing to a well-functioning immune defense
  • Counteracting inflammation

Selenium yeast lowers the risk of colon cancer and other cancer forms

Back in 1996, the (now deceased) American cancer researcher, Professor Larry Clark, documented that supplementation with selenium yeast could lower the risk of colorectal cancer by nearly 60 percent. Larry Clark originally wanted to see if selenium could prevent recurrence of benign skin cancer. In his groundbreaking NPC study (Nutritional Prevention of Cancer), 1,312 patients with benign skin cancer were randomly assigned to either 200 micrograms of selenium yeast daily or matching placebo. Six years later, when the researchers broke the code to find out who had been taking what, they discovered that selenium supplementation did not have a significant impact on skin cancer. However, it turned out that the selenium had a massive effect on several other cancer forms. It turned out that in the group of patients who had taken selenium, there were:

  • 58% fewer cases of colorectal cancer
  • 63% fewer cases of prostate cancer
  • 46% fewer cases of lung cancer
  • 50% lower all-cause cancer mortality

Selenomethionine supplements do not work. Studies are misleading

In a larger study (the SELECT study) that was conducted later, scientists tested the effect of selenium and vitamin E. However, this study did not show any protective effect on cancer. This is because they used a form of selenium called selenomethionine. Contrary to selenium yeast, selenomethionine has no documented anti-cancer properties. Moreover, they used a synthetic vitamin E source. It is therefore misleading to use the SELECT study as leverage for discouraging people from taking selenium to prevent cancer. It would be far more correct to inform that selenomethionine most probably does not work and to recommend selenium yeast, instead.

When discussing studies of minerals, one should always make a note of the form that is used

Many minerals occur in different forms that have widely different effects in the body. Consequently, there is a big difference between consuming sodium in the form of table salt (sodium chloride) or baking soda (sodium hydrogen carbonate/sodium bicarbonate). Similarly, there is a difference between taking selenium as selenium yeast or selenomethionine. There are also large differences when it comes to the bioavailability and quality of different nutritional supplements on the market. Always make sure to check if the manufacturer can document the bioavailability of his product.

It is difficult to get enough selenium, even with a balanced diet

Selenium in its different organic forms is mainly found in fish, shellfish, offal, eggs, dairy products, and Brazil nuts. However, Danish crops are generally low in selenium, and although fish and shellfish as such are considered good selenium sources, it is not possible to get adequate amounts of selenium by eating seafood five days a week. This was demonstrated in a study that was carried out in collaboration with the Danish Cancer Society several years ago. Selenium supplements can easily compensate for the low selenium content in our diet, especially preparations with selenium yeast, which contain a variety of different selenium species similar to the variety found in a balanced diet.

Important note: The nutrient depletion of European soil increases the risk of selenium deficiencies

A team of scientists from the Swiss Federal Institute of Aquatic Science and Technology conducted a thorough analysis of soil samples taken from 1994 to 2016, looking at how the selenium content in the top soil changed over time. By holding selenium levels in soil up against 26 environmental variables, the scientists were able to see how the selenium content would continue decreasing until the end of the century.

How to compensate for the decreasing selenium intake and saturate selenoprotein P

An estimated 20 percent of the Danish population has a dietary selenium intake that is below the reference intake level (RI). However, according to research, even the RI level of 55 micrograms is not sufficient to properly saturate selenoprotein P, which is an important marker of selenium status in the human body. In order to saturate this selenoprotein, one would need to consume 100-125 micrograms of selenium every day, which is around twice as much as the current recommendations.

Your risk of colorectal cancer inceases

  • the older you are
  • if you have a family history of the disease
  • if you eat too little fiber and too much red meat (from four-legged animals)
  • if you are overweight
  • if you smoke
  • if you take a lot of medicine
  • if you lack selenium


Sundhedsstyrelsen. Tilbud om undersøgelse for kræft i tyk- og endetarm

New Links between selenium and cancer prevention. HRB. December 2017

Clark LC et al: Effects of Selenium Supplementation for Cancer Prevention in Patients with Carcinoma of the Skin. JAMA: 1997.

Klein EA et al. Vitamin E and the risk of prostate cancer: The Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA 2011.

Bonelli et all. Antioxidant supplement and long-term reduction of recurrent adenomas of the large bowel. A double-blind randomized trial. J. Gastroenterol 2013

Bonelli Luigina. Reduction of the Incidence of Metachronous Adenomas of the Large Bowel by Means of Antioxidants". Colon Cancer Prevention 1999

Lutz Shomburg. Dietary Selenium and Human Health. Nutrients 2017

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