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Prevent sverity and duration of cold and flu

Reduce Cold, Flu, and Allergy Symptoms

Researchers identified two compounds that in clinical trials helped prevent colds and flu and reduce severity and duration when they occur.

Scientifically reviewed by: Amanda Martin, DC, in March 2024. Written by: Heather L. Makar.

Colds and allergies make millions of people miserable every year.

The flu causes tens of thousands of U.S. deaths in a typical year.1

Human studies demonstrate how two ingredients help prevent colds and flu and reduce the severity and duration of symptoms when they do occur.

In a clinical study of school children, consumption of yogurt containing the probiotic L. rhamnosus CRL1505 resulted in approximately:2

  • 55% fewer cold and flu occurrences, and
  • 48% fewer cases of fever.

In other human studies, yeast fermentate cut days of suffering from nasal congestion during peak allergy season by 43%3 and reduced cold and flu symptoms during winter.4

Both these ingredients boost the activity of an antibody that provides strong immune responses against viruses and bacteria.5,6

Fighting Colds and Flu

American adults get an average of two to four colds annually.7

Colds, flu, and seasonal allergies cause 75% of all employees miss some work with an average time out of work of two to three days per upper respiratory episode.8

Researchers have identified two compounds, a probiotic2 and a dried yeast fermentate,4 that can help prevent colds and flu and their symptoms and reduce their severity and duration when they occur.

Probiotics are beneficial bacteria. Their formal definition is “living microorganisms that promote health when ingested in sufficient amounts.” The specific strain Lactobacillus rhamnosus CRL1505 can enhance immunity against respiratory infections.5,9

Using a proprietary fermentation process, scientists created a special dried fermentate of baker's yeast (S. cerevisiae).

The fermentate helps promote the body's healthy immune response by increasing the antibody secretory IgA.10,11

Secretory IgA is known to block pathogens from penetrating mucosal surfaces,12,13  which may provide protection from environmental triggers of allergies, such as pollen.

Yeast fermentate is rich in beta-glucans, complex carbohydrates shown to have immune-enhancing effects such as supporting activity of natural killer cells.14,15

Avoid Allergy Drug Side Effects

While over-the-counter medications can provide temporary relief from cold, flu, and allergy symptoms, they don't impact the frequency or duration of these illnesses.

Side effects from drugs for seasonal flu and allergic rhinitis include drowsiness, headaches, rapid heartbeat, and sleep problems.16 Some allergy medications, such as anticholinergics, are associated with increased risk of cognitive impairment.17,18

The probiotic Lactobacillus rhamnosus CRL1505 and yeast fermentate are associated with little to no adverse effects.

An Immunity-Boosting Probiotic

L. rhamnosus CRL1505 was originally isolated from goat's milk in Argentina.5

Cell and animal research has found that this probiotic can improve innate respiratory immunity, increase levels of anti-pneumococcal antibodies (which fight a wide range of infections),19 and reduce the inflammatory response that causes some cold/flu symptoms.20,21

A human study found that oral use of this probiotic significantly increases levels of antibodies known as immunoglobulin A (IgA).2

These antibodies are secreted from mucous membranes including the nose, mouth, and lungs, and can block viruses that cause colds and flu from invading cells and causing infection.

What You Need To Know

Reduce the Misery of Colds, Flu, and Allergies

  • In a clinical trial, the probiotic strain Lactobacillus rhamnosus CRL1505 reduced cold and flu occurrences by 55%, infections by 49%, and fevers by 48% over six months.
  • Taking dried yeast fermentate also reduced cold and flu symptoms and dramatically reduced symptoms of seasonal allergies, leading to 43% fewer days with nasal congestion.
  • These ingredients boost aspects of the immune system, including natural killer cell activity and antibodies against viruses and bacteria.
  • A combination of yeast fermentate and L. rhamnosus CRL1505 may help decrease the frequency, duration, and severity of allergies, colds, and flu.

Preventing Infections

In Argentina, scientists enrolled preschool children attending day care centers in a placebo-controlled study of a yogurt containing the L. rhamnosus CRL1505 probiotic strain.

Over a six-month period, compared to a group receiving yogurt without the probiotic, children receiving 100 million CFUs (colony-forming units) of L. rhamnosus CRL1505 five days a week had:

  • 55% fewer cold and flu occurrences,
  • 48% fewer instances of fever,
  • 49% fewer overall infections, and
  • 47% higher levels of beneficial secretory IgA.

The treatment group also had 61% fewer cases of tonsillitis and pharyngitis (a throat infection).

These results captured the attention of the Argentinian government, which has been distributing the probiotic yogurt to more than 200,000 children annually since 2008.2

Yeast Fermentate Strengthens Immunity

The effects of yeast fermentate were discovered unintentionally when it was noticed that factory workers in Cedar Rapids, Iowa, who inhaled the yeast daily, took significantly fewer sick days than their office-worker counterparts.6

This observation led to multiple human studies, which found that oral intake of dried yeast fermentate resulted in:3,6,15,22,23

  • Increased levels of secretory IgA, the antibody providing mucosal immune defense against viruses and bacteria, and
  • Increased activity of natural killer cells, immune cells that are part of the first line defense against infected cells.

A company in Iowa went on to develop a dried yeast fermentate using baker's yeast. At least five placebo-controlled clinical trials have since validated its protection against colds, flu, and allergies.15,22,23

In one clinical trial, taking 500 mg of dried yeast fermentate daily from January through March (peak cold and flu season) led to a 13% reduction in cold or flu symptoms, compared to a placebo group.4

In a similar study, the same dose reduced the duration of cold and flu symptoms by 17%.24

Relief for Allergy Symptoms

Yeast fermentate also helps relieve symptoms of seasonal allergies.

Allergy symptoms are primarily caused by immunoglobulin A (IgE) antibodies, which trigger the body's release of chemicals such as histamine that cause these reactions.

Yeast fermentate has shown an ability to prevent IgE levels from rising too much, reducing allergic reactions.23

In a pilot study, adults were given a placebo or 500 mg of dried yeast fermentate daily for five weeks during allergy season. Symptoms were unchanged in the placebo group, while half of those taking yeast had a complete absence of allergy symptoms. Symptoms returned within two weeks of stopping the yeast fermentate.23

A larger clinical study of adults with seasonal allergies and hay fever showed that those taking 500 mg of dried yeast fermentate daily had 43% fewer days with nasal congestion and reduced severity of runny noses and congestion.3

Taking yeast fermentate and L. rhamnosus CRL1505 together may help provide broad protection against colds, flu, and allergies.


In separate clinical studies, dried yeast fermentate and the probiotic L. rhamnosus CRL1505 significantly reduced the severity, frequency, and duration of symptoms associated with colds and flu.

Yeast fermentate also reduced allergy symptoms.

These two ingredients have been found to enhance immune defenses against viruses and bacteria in numerous ways.

If you have any questions on the scientific content of this article, please call a Life Extension Wellness Specialist at 1-866-864-3027.


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