S. Boulardii and Hashimoto’s

Saccharomyces boulardii or S. boulardii is often referred to as a probiotic, but it is actually a beneficial yeast that is usually taken in the form of a dietary supplement. It has been used clinically for over 50 years, originally to prevent and treat infectious diarrhoea.

However, S. boulardii has been used traditionally as a component of herbal preparation for hundreds, if not thousands of years, long before scientists were able to identify and classify bacteria or yeasts.

S. Boulardii

S.boulardii is named after the French microbiologist who discovered it, Henri Boulard. The story goes something like this: In the 1920s, Boulard was in Indonesia, where medicinal tea was used as a treatment for cholera-associated diarrhoea.

Boulard discovered that the tea, which contained mangosteen peel and lychee, owed its medicinal properties to S. boulardii, which was able to multiply at high temperatures. Upon his return to France, Boulard patented his discovery. Official research and publications on the species began in the 1940s and 1950s.

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We now know that by crossing the digestive system, S. boulardii helps to cleanse the intestine and improve the microbial balance, but does not take up residence in the intestine by multiplying there. 

probiotic in gut

Instead, it helps remove and eliminate opportunistic and pathogenic organisms such as yeasts, bacteria, and parasites from the gut. In other words, S. boulardii helps establish a healing environment in the gut and takes pathogens with it when they leave the body through the stool. This helps prevent new infections and reinfections.

S.boulardii has been shown to help produce secretory IgA, an immunoglobulin (antibody) that plays a crucial role in the immune function of the body's mucosa and helps provide a protective barrier (SIgA is the first line of defence of the respiratory tract and stomach - intestinal tract). 

It can prevent the attachment of viruses, bacteria, parasites, and other pathogens to our respiratory tract and intestinal mucosa. Numerous studies have shown better results for various infections, as well as cancer and intestinal problems, with S. boulardii supplementation.

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What conditions may benefit from S.boulardii?

Most research on S. boulardii over the years has focused on the conditions that cause diarrhoea. These include pathogenic diarrhoea (bacterial, viral, fungal), traveller's diarrhoea, HIV-related diarrhoea, antibiotic-associated diarrhoea, Clostridium difficile infections, and others.


The reason S. boulardii works so well against diarrhoea is that it stimulates the release of immunoglobulins (antibodies) and chemical messengers (like cytokines) and supports the maturation of immune cells. Because S. boulardii binds to pathogenic bacteria, it can neutralize toxins and decrease pathogens clinging to the walls of the digestive system. Essentially, it calms an overactive immune response in the digestive system.

Scientific literature suggests that S. boulardii is safe and beneficial even for acute diarrhoea in children. It can also be used with antibiotics to prevent gastrointestinal symptoms. Me too S. boulardii is used in combination with antibiotics to prevent dysbiosis, an imbalance of gut bacteria that often occurs as a result of antibiotic use.

inflammation in gut

Also, s. boulardii benefits the gut by reducing inflammation in the digestive system and helping to repair leaky gut.

Due to the immune and gut protective effects of S. boulardii, a recent study looked at this supplement for several different conditions, including:

  • Parasites, such as Blastocystis hominis 
  • Irritable bowel syndrome (IBS) 
  • Inflammatory bowel disease (IBD) 
  • SIBO (small intestinal bacterial overgrowth) 
  • Lyme disease 
  • Candida (yeast) infections 
  • Urinary tract infections 
  • H. pylori 
  • Mold exposure 


What's interesting about this list is that these conditions are often considered a cause of Hashimoto's or a co-diagnosis or symptom in my clients.

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How does S. boulardi benefit Hashimoto's?

Although there are no current studies specifically examining the direct effects of S. boulardii on Hashimoto's or thyroid health, S. boulardii. boulardii can help address some of the underlying causes of autoimmune thyroiditis.

Gut health 

Improving gut health and fighting infection are key factors in achieving Hashimoto's remission, and as mentioned above, S. boulardii can help with both.

gut health

Hippocrates had the idea that "all disease begins in the gut," and Hashimoto's is no exception. Hashimoto's disease and all autoimmune diseases require three factors: genetic predisposition, environmental triggers (such as heavy metal toxicity or infection), and leaky gut (gut permeability). This is called the autoimmune tricycle. 

A leaky gut occurs when the connections between the epithelial cells (the cells that line the small intestine) become loose or leaky.

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Because S. boulardii induces SIgA, Blastocystis hominis, H. pylori, Candida, SIBO, Giardia and other common infections in Hashimoto's patients.


Blastocystis hominis is a common parasite in people with Hashimoto's disease that can be associated with chronic hives and uncomfortable IBS symptoms.

  1. pylori is another gastric bacterial infection that can cause Hashimoto's thyroiditis. H. pylori can cause low stomach acid, nutritional deficiencies, inflammation and leaky gut. Although S. boulardii did not self-medicate, H. pylori reduce curative symptoms (eg, diarrhoea and nausea) and prevent dysbiosis.

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Candida overgrowth

A third intestinal infection that can cause Hashimoto's disease in some cases is Candida overgrowth, and S. boulardii supplements can also support Candida treatment. S. boulardii is a probiotic yeast, so it can help eliminate pathogenic strains of yeast like Candida and balance it with the rest of the organisms in the colon. 


Small intestinal bacterial overgrowth (SIBO) is a gut disorder that many people with Hashimoto's disease have. In SIBO, bacteria, and yeast move from the large intestine to the small intestine, which usually contains much fewer bacteria than the large intestine. Overgrowth of these bacteria ferments food and causes gas, bloating, constipation, or diarrhoea, among other things.

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Mold toxicity

Mold toxicity is another possible cause that we have seen in Hashimoto's disease. If you are exposed to a moldy environment, there is a good chance that fungus has colonized your body, including your intestines and sinuses. 


In addition to eliminating the cause of the fungus, additional procedures may be necessary to eliminate the fungus from the body. Mold in the sinuses and intestines can lead to loss of the gut and lead autoimmune disease.

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S.boulardii is one such supplement considered to be generally safe and effective in treating some of the underlying causes and symptoms of Hashimoto's disease, such as antibiotic-induced microbiome imbalances, adrenal dysfunction, and certain intestinal infections. If you're dealing with digestive issues, looking for ways to support your adrenal health, or just want to boost your overall immune system, adding S. boulardii to your routine can help.


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