Selenium’s and iron’s different roles in cancer prevention

 – and why it is vital to get the exact right amount!

Selenium’s and iron’s different roles in cancer preventionAll our cells contain different selenium compounds that support a number of vital functions, and which have several cancer-fighting mechanisms. As an antioxidant, selenium prevents iron from developing some of the most harmful free radicals that can damage cellular DNA and lead to uncontrolled cell division. This is why a selenium deficiency combined with excess iron is a lethal cocktail. Although iron is essential, it is vital that we do not get too much. It is also important to get plenty of selenium from food and/or supplements and in a form that the body can absorb and utilize in each and every cell in order to be properly protected against cancerous substances.

Each and every cell in our body – there 1013 (or 10,000,000,000,000) of them – is specialized to undertake specific tasks. The cell membrane is the outer shield that protects against external threats. All interactions between the cells and its surrounding environment are handled by membrane proteins. Inside the cells are different organelles such our genetic coding (DNA) that switches on or off special functions in the cell. The mitochondria are the cellular powerhouses that convert fat, carbohydrate, and protein into energy (ATP) by means of oxygen and Q10. All cells, however, are vulnerable, and their worst enemies are the free radicals that are like internal terrorists that are capable of transforming healthy cells into cancer cells, provided the cells are not properly protected.

Free radicals and antioxidants are key words in the development and prevention of cancer

Free radicals are a byproduct of human respiration. We generate more free radicals when we are exposed to stress, or as a result of ageing processes, poisoning, smoking, and radiation. Free radicals attack cell membranes, starting chain reactions among and inside the cells that attack their DNA and mitochondria.
Our only protection against free radicals are various antioxidants, especially the essential nutrients vitamin A, vitamin C, vitamin E, selenium, and zinc. Selenium plays a particularly important role in cancer prevention, but only if we get adequate amounts of this nutrient.
At a cellular level, selenium is a part of the active antioxidant, glutathione peroxidase (GPx) that serves as first-line defense against free radical attacks on cells. Especially a free radical like hydrogen peroxide, which is a byproduct of cellular energy metabolism, is a key activator of some very dangerous and harmful free radicals.

Too much iron and lack of selenium is a lethal cocktail

Iron is included in the hemoglobin of red blood cells that supplies oxygen to the body’s different cells and tissues. Iron is also a catalyst of free radicals, which is why we must be careful not to have too much iron in the body. Inside the mitochondria of the cells, iron is able to instigate a so-called Fenton reaction where iron reacts with hydrogen peroxide to form hydroxyl radicals – the most harmful free radicals we know of.

Free radicals start by attacking the mitochondria

Hydroxyl radicals start by attacking mitochondrial DNA, proteins, and cell membranes, thereby stifling the energy turnover and various other functions of the cell, causing it to die prematurely. It is therefore important not to consume more iron than is needed, and it is normally a good idea to have your iron levels checked. Ideally, iron levels must lie in the range of 40-60 ng/ml of blood.
Apparently, many people have excess iron in their blood. The problem is common with those who consume large quantities of meat or take iron supplements without actually needing them. Children primarily lack iron, and the same is the case with women of childbearing age due to the iron that is lost with their menstrual bleeding. In other words, we need sufficient amounts of iron but not too much. At the same time, it is vital to get enough selenium to ensure proper selenium saturation of the selenium-dependent GPx proteins and other selenoproteins so they can exert their cancer-protective properties.

200 micrograms of selenium yeast may lower cancer risk and cancer mortality by over 50%

Baron Jöns Berzelius, a Swedish chemist, discovered selenium around 200 years ago. Ever since, scientists have been busy investigating the role of selenium in human health, especially its ability to counteract inflammation and cancer.
In 1996, the American scientist Larry Clark demonstrated with his NPC study (Nutritional Prevention of Cancer) that daily supplementation with 200 micrograms of selenium yeast was able to lower the risk of three common cancer forms by 46-63 percent, while reducing cancer mortality by 50%. This study made science realize the important role of the selenium-dependent GPx antioxidants and their ability to neutralize free radicals.

Supplementation with selenomethionine is ineffective, and studies are misguiding

Unfortunately, the more recent SELECT study clouds the picture results. In this study, researchers also used supplements of selenium (and vitamin E), but no cancer reducing effect was observed. The reason for this is that the scientists used selenemethionine, a form of selenium that, unlike organic selenium yeast, has not demonstrated any cancer-protective potential. Moreover, the scientists used a synthetic form of vitamin E.
It is therefore misleading to refer to the SELECT study in an attempt to discourage people from taking selenium supplements. It would be more correct to inform the public that selenomethionine supplements cannot be expected to have any effect and recommend organic selenium yeast, instead.

It is vital to take the right kind of selenium

As mentioned earlier, all our cells contain selenium. The nutrient supports around 30 different selenium-dependent proteins (selenoproteins) that control energy turnover, metabolism, and immune defense. Also, they serve as antioxidants and have many other functions
Selenium yeast contains a host of different selenium compounds. It provides the same selenium variety that we have inside our cells or that can be found in a balanced diet consisting of many different selenium sources like fish, organ meat, eggs, and Brazil nuts.
In other words, selenium yeast provides selenomethionine but it also provides methylselenocysteine, selenocysteine, and other selenium compounds. Scientists believe that methylselenocysteine, which is converted into methylselenol, may be one of the most active selenium compounds when it comes to preventing cancer.
Researchers from the University of Copenhagen have published a study that investigates how methylselenol inhibits cancer cell proliferation caused by cellular stress and a derailed immune defense. Selenium yeast is known to contain methylselenocysteine, which is not found in ordinary selenium supplements containing selenomethionine, selenate, or selenite.
As described, selenium is more than just plain selenium. In fact, the devil is in the detail when studies conducted with simple, inorganic selenium forms fail to show positive results. Leading researchers therefore believe that the actual combination of different selenium compounds in food sources and selenium yeast supplements is what influences cellular function and cancer protection.

Selenium is more than just selenium

Selenium supports around 30 different selenoproteins.
Science believes that methylselenocysteine that is converted into methylselenol may be one of the most active selenium compounds in cancer prevention.
Selenium yeast contains methylselenocysteine and numerous other selenium compounds that give the same variety as found inside our own cells.

Other known cancer-protective properties

Selenoprotein P is able to repair DNA damage and prevent healthy cells from turning into cancer cells. Selenium generally strengthens the immune system and bolsters its ability to attack cancer cells. Other selenoproteins are able to neutralize cancerous toxins such as mercury. The different selenoproteins also counteract two traits that are characteristic of cancer cells. One is their formidable ability to form new blood vessels while spreading (angiogenesis). The other is their lacking ability to self-destruct (programmed cell death or apoptosis). This is what normal cells do when they are no longer able to function normally.

Less cancer in countries with high selenium intake

In 1977, the American scientist Gerhard Schrauzer from San Diego University mapped out cancer mortality in 27 different countries. He observed that the higher the selenium intake in the individual country, the lower its cancer mortality.

Impaired selenium status long before the cancer shows

In many cases, 10-15 years pass from the occurrence of the first cell mutation until a tumor is detected. Meanwhile, lack of selenium leaves cells increasingly vulnerable, whereby they can more easily mutate and spread inside the body. Several large studies have shown differences in blood selenium levels between cancer patients and healthy controls long before the disease manifests itself. Because cancer often takes years to develop, selenium is a crucial key to long-term prevention.

Widespread selenium deficiency in Europe

The European soil contains very little selenium. Low intake of fish and organ meat contributes to the widespread deficiency problem. Smoking, alcohol abuse, mercury poisoning, Crohn’s disease, and ulcerative colitis may also deplete the body’s selenium levels.

How much selenium do we need?

The official recommendation for selenium is around 50-60 micrograms daily. However, studies show that this intake level is not sufficient to ensure proper saturation of selenoprotein P, which is a marker for selenium status in the blood. It takes around 100 micrograms of selenium daily to saturate selenoprotein P. When it comes to cancer prevention specifically, researchers recommend 200 micrograms daily, which is the dose that was used in the NPC study. This study showed a 50% reduction of cancer mortality.
Studies using 400 micrograms of selenium/day have not shown better results, and selenium can even be toxic if ingested in very high doses. Daily intake levels of up to 300 micrograms are considered safe but they are probably not necessary.

If we want to protect ourselves against cancer, we must make to get enough selenium to saturate the different selenoproteins that work by:

  • protecting cells against free radicals
  • repairing DNA damage
  • neutralizing environmental toxins like mercury
  • inhibiting the formation of new blood vessels in tumors (angiogenesis)
  • helping diseased cells self-destruct (apoptosis)
  • contributing to a well-functioning immune system
  • controlling the production of compounds that overstimulate the immune defense


Mercola. The role of Selenium in Cellular Health and Cancer prevention. 2015

Clark LC et al: Effects of Selenium Supplementation for Cancer Prevention in Patients with Carcinoma of the Skin. Journal of the American Medical Association. 1996

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

Hagemann-Jensen Michael et al. The Selenium Metabolite Methylselenol Regulates the Expression of Ligands That Trigger Immune Activation through the Lymphocyte Receptor NKG2D. The Journal of Biological Chemistry. 2014.

Heath, J.C. et al: Dietary selenium protects against selected signs of aging and methylmercury exposure. Neurotoxicology, 2010.

Hertz Niels. Selen et livsvigtigt spormineral. Ny Videnskab 2002.