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Selenium deficiency and how it affects the gut flora, intestinal diseases, and mental health

Selenium deficiency and how it affects the gut flora, intestinal diseases, and mental healthSelenium is an essential trace element of vital importance to our general health. The nutrient is also important for our gut flora, and being selenium-deficient may increase the risk of irritable bowel syndrome, inflammatory gut diseases like Crohn’s disease and ulcerous colitis, and even bowel cancer. Our intestine is also called our “third brain” because both our gut flora and digestion have a significant influence on our mental well-being, according to a review article published in Frontiers in Nutrition. The authors focus on selenium because selenium deficiencies are common in China, Europe, and many other places, and supplementation may be necessary.

According to the new review article, which is authored by scientists from Wuhan in China, our enormous gut flora consists of more than 100 trillion microorganisms, including bacteria, viruses, fungi, and protozoa. Our gut flora codes for more than three million genes and handles a host of essential processes. Having a healthy gut flora helps us by:

  • Ensuring proper absorption of dietary nutrients
  • Producing vitamins and enzymes
  • Producing serotonin (a neurotransmitter)
  • Producing lactic acid and maintaining a normal pH value
  • Warding off harmful microorganisms
  • Metabolizing indigestible carbohydrates (fibers)

It is important for the different microorganisms in the gut flora to coexist in a delicate balance to maintain the essential ecosystem (symbiosis).
If this intestinal symbiosis is disrupted, a dysbiosis may occur, causing some species to be suppressed and others to dominate. For example, local bacteria and fungi may replicate and set the stage for digestive problems and infections. Also, various types of inflammatory conditions such as Crohn’s disease and ulcerous colitis may occur. A dysbiosis of the gut flora is even a key factor in the development of other conditions like cancer, diarrhea, and autism. They may be a result of different factors such as antibiotic use, unhealthy diets, lack of fiber, various types of medicine, stress, and lack of nutrients. The Wuhan scientists focused specifically on selenium because selenium deficiency is so widespread.

How does selenium affect our health, gut flora, inflammation, and mental health?

Selenium is of importance to our energy turnover, thyroid function, immune defense, and many other functions. The nutrient supports well over 25 different selenium-dependent proteins (selenoproteins) that serve as enzymes and antioxidants. One of the most important antioxidants is GPX (glutathione peroxidase). It counteracts oxidative stress and cell damage caused by free radicals.
With regard to the gut flora, selenium supports certain bacteria’s enzyme function, and selenium appears to have a direct influence on the intestinal flora and its condition. It appears that a specific selenium-rich lactic acid bacteria named Lactobacillus rhamnosus SHA113 can counteract intestinal damage by forming an insoluble protective compound.
Selenium is important for the intestinal immune defense that must be able to fight off pathogens and toxins from food. Selenium’s anti-inflammatory effect is a result of specific white blood cells (macrophages) shifting from being pro-inflammatory to anti-inflammatory with help from selenium. That way, the intestinal epithelial cells (IECs) that serve as a barrier are able to restitute much faster.
In their review article, the authors also refer to the intestines as the “third brain” and mention that our gut flora and digestion are of huge importance to our mental well-being. A healthy gut flora produces certain B vitamins, enzymes, and serotonin (a neurotransmitter), all of which are important for our mental wellbeing. It is also well-known that constipation can affect our mood. This is because toxins that would normally be secreted in the feces are reabsorbed by the colon and poison the body.
The authors conclude that a selenium deficiency is able to change the healthy bacterial flora in a negative direction, which paves the road for inflammatory bowel disease, thyroid disorders, cancer, and other diseases. Although there is a lot of research in this area, science still hasn’t found the optimal selenium levels for the gut flora. One of the reasons is that the majority of gut bacteria are difficult to cultivate.

Selenium deficiency and intestinal diseases

Colorectal cancer is one of the leading causes of cancer death in Europe. In 2015, researchers from 10 European countries looked at the relation between selenium deficiency and colorectal cancer in over 500,000 people. They found that low selenium levels in the blood were linked to an increased risk of colorectal cancer, while having high blood levels of selenium lowers the risk.
Experts from Penn State University in the United States have found that low selenium levels in the blood are related to an increased risk of developing inflammatory bowel diseases like Crohn’s disease and ulcerous colitis.

Where do we get selenium and why are deficiencies so common?

Some of the best selenium sources are grains, offal, meat, fish and seafood, and nuts (especially Brazil nuts). In over 70 percent of China, however, the selenium level in the soil is low. The same is the case with the farmland in Europe and many other parts of the world. This problem is reflected in the crops and it is one of the main reasons why the selenium intake in different parts of the world varies massively. In many cases, it may be necessary to take a supplement. Organic selenium forms are easier for the body to absorb and utilize compared with inorganic selenium forms. In most scientific studies of selenium, scientists have used daily doses of 100-200 micrograms. According to WHO, the safe upper intake level for selenium is 400 micrograms daily.


Jinzhong Cai et al. Advances in the study of selenium and human intestinal bacteria. Frontiers in Nutrition. 14 December 2022.

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