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Your Digestive System Can Protect You From Colds and Flu

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Probiotics are known for their positive effects in the gastrointestinal tract. However, recent evidence shows that they can provide even more benefits outside the gut. Because the gut is wired to the immune system, probiotics can also enhance immune functions. Studies show that the key to protecting you from cold and flu may lie in your digestive system. How do probiotics prevent and treat cold and flu? Do probiotics affect the efficacy of flu shots? Can all probiotics protect your from colds and flu? Read on to find out.

What Are Probiotics?

Probiotics are live microbes that can provide certain health benefits for the host. While most probiotics are bacteria, there are a few yeasts that qualify.

Probiotics are also referred to as “good” and “beneficial” microbes. At any point in time, the gut is populated by microbes. Most of these beneficial microbes are bacteria and they outnumber human cells in population.

Beneficial bacteria in the gut make up healthy gut flora. These microbes prevent the overgrowth of pathogens, improve digestion and absorption, help synthesize vitamin K, maintain the pH of the gut and keep the immune system properly challenged without being overwhelmed.

However, when pathogens outnumber beneficial bacteria in the gut, the imbalance that results leaves the body open to infections and other diseases.

Probiotics are recommended to restore healthy gut flora. Therefore, probiotics can help reverse the damage done to the gut flora by antibiotics, poor diet, stress, diseases, and hormone imbalance.

Most probiotics belong to two bacteria families: Bifidobacterium and Lactobacillus. Examples of such bacteria are Bifidobacterium bifidus and Lactobacillus acidophilus.

Certain foods are excellent sources of probiotics. Examples of these are fermented dairy products such as yogurt. Other dietary sources of probiotics are kefir and soy products such as miso and tempeh.

Besides foods, probiotics are also available as dietary and health supplements.

Conditions Treated with Probiotics
  • Diarrhea especially antibiotic-associated diarrhea
  • Irritable bowel syndrome
  • Eczema
  • Respiratory tract infections such as cold and the flu
  • Peptic ulcer
  • Dental caries

How Probiotics Can Help Colds and Flu

Probiotics can help your colds and flu by boosting the immune system. Most of the studies investigating the benefit of probiotics used specific strains of probiotics.

Evidently not all “beneficial bacterial” are helpful for preventing and/or treating cold and the flu.

Since the gut is the gateway to the body, it serves as a physical barrier against pathogens, toxins and undigested food particles.

Therefore, most of the immune system is directed to preserve the gut barrier and quickly address any breach from there. To this end, healthy gut flora is essential to a functional immune system.

When probiotics restore the gut flora, they allow the immune system to fully recover and combat the pathogens and toxins in the systemic circulation. However, probiotics do more than that. They increase the production of immunoglobulins and specialized immune cells such as T lymphocytes and NK (Natural Killer) cells.

Besides increasing the production and release of immune cells, probiotics also enhance the activities of these cells.

Studies have confirmed that probiotics improve phagocytosis and, therefore, the ability of white blood cells to engulf and destroy viruses such as cold and influenza viruses.

Can the beneficial effects of probiotics on the immune system translate to shorter cold and flu episodes? According to the results of multiple studies and a Cochrane review, yes. In addition, probiotics are most effective against cold and flu in children.

The evidence is rather strong that probiotics reduce both the duration and severity of colds and the flu.

In addition, probiotics can improve immune response to flu vaccines. This is especially important because flu shots are the primary preventative intervention recommended every flu season.

Every year, more and more people choose to get vaccinated against influenza viruses and yet every year, more people come down with colds and the flu. One reason for this outcome is because the vaccine does not trigger a significant response from the immune system to confer full protection on the immunized.

However, reports show that those who take probiotics along with flu vaccines are far less likely to catch a cold or come down with the flu.

How can probiotics improve the efficacy of flu shots? By boosting the immune system.

Probiotics can increase the production of specific antibodies that combat antigens produced by cold and flu viruses. Therefore, these beneficial microbes can help the immune system quickly and efficiently respond to the viral challenge and protect the body against subsequent viral infections.

Lastly, the anti-inflammatory property of probiotics also makes them useful for relieving cold and flu symptoms. Probiotics contribute to the regulation of cytokine functions. Therefore, they modulate inflammatory and hypersensitivity reactions.

These anti-inflammatory and immunomodulatory effects are also responsible for the efficacy of probiotics for preventing and/or treating inflammatory bowel disease, lactose intolerance, and milk allergies.

Studies on Probiotics, Colds and Flu

Probiotics and Stressed-Induced Cold and Flu

A 2010 study published in the Journal of the American College of Nutrition investigated the effect of a fermented dairy product on common respiratory and gastrointestinal infections among shift workers.

Shift workers are known to be immunocompromised and, therefore, carry higher risks of colds and the flu than the general population. For this study, the researchers recruited 100 shift workers as volunteers. Half of them were given a placebo while the other half received 200 g/day of the probiotic, verum (Lactobacillus casei DN-114 001) for 3 months.

After allowing a follow-up period of 1 month, the researchers observed that the probiotic group had fewer cases of respiratory and gastrointestinal infections.

In addition, probiotics reduced the duration of fever due to infection and reduced sick days even among the smokers in the probiotic group. The researchers also showed that probiotics increased the levels and activities of immune cells such as leukocytes, neutrophils, and NK (natural killer) cells.

The researchers, therefore, concluded that probiotics are safe, well-tolerated and effective for boosting the immune system and lowering the risk of common infections even in those under significant stress.

In a 2012 study published in the journal, Human Kinetics, researchers also investigated the benefits of probiotics for treating common cold among another group of stressed individuals: endurance athletes.

The researchers recruited 66 men and women engaged in high-intensity endurance physical activities during a 4-month spring training program.

Half of them were given the probiotic, Lactobacillus salivarius, while the other group was placed on placebo.

The results of the study showed that there was no difference between the two groups. Neither the presentation/incidence of cold symptoms nor immune functions differed between both groups.

This study highlights the fact that not all probiotics can protect or treat your cold or flu. Even though the probiotic used in this study belonged to the Lactobacillus group, it was an ineffective strain.

Therefore, you need to choose specific strains of probiotics proven to prevent and/or treat colds and the flu.

Can Minerals and Vitamins Help?

A 2011 study published in the European Journal of Nutrition also investigated the benefits of other Lactobacillus species in the treatment of a common cold. The study involved 272 healthy volunteers and the probiotics, Lactobacillus plantarum and Lactobacillus paracasei.

The results of this study showed that, compared to the control group, those who took probiotics had lower risks of the common cold (55% vs. 67%), shorter duration of cold symptoms (6.2 days vs. 8.6 days) and fewer symptoms.

The researchers, therefore, concluded that the probiotics used were safe and effective for reducing the risks of acquiring common cold infections.

A 2005 study published in the journal, Clinical Nutrition, confirmed the same benefits for Bifidobacterium species.

The 3-month study spanning winter and spring involved 479 healthy adults who took vitamins and minerals with or without the probiotic bacteria, Lactobacillus gasseri, Bifidobacterium longum, and bifidum.

The results showed that those who took probiotics had fewer sick days and fewer cold symptoms than those who did not. In addition, the results showed that probiotics enhanced the activities of immune cells such as monocytes, leucocytes and the lymphocytes, cytotoxic T suppressor cells or CD8+ and T helper cells or CD4+.

In conclusion, the researchers believed that the probiotics used were effective for boosting the immune system and reducing both the duration and severity of cold symptoms.

But did the vitamins and minerals used by the probiotic group improve the efficacy of probiotics?

A reinterpretation of the results published in the International Journal of Clinical Pharmacology and Therapeutics in the same year indicated that vitamins and minerals likely enhanced the positive effects of probiotics on the immune system.

Probiotics for Children

One of the oft-quoted studies in this field of research is a 2009 study published in the journal, Pediatrics.

The double-blind, placebo-controlled study involved 326 children aged 3 – 5 years. While 104 of these children were placed on placebo, the rest received probiotics. Of these, 110 were given Lactobacillus acidophilus and 112 received the same probiotic plus Bifidobacterium animalis subsp lactis two times daily for 6 months.

The results of the study showed that both probiotic groups performed better than the control group.

From the results, the incidence, severity, and duration of fever, cough, and rhinorrhea were reduced significantly in the probiotic groups. In addition, probiotics reduced antibiotics use and the number of days absent from school due to sickness.

The children who received the combined probiotics got the best benefits.

This study demonstrated that probiotics are safe even for children and can help prevent and treat cold and flu symptoms in this age group.

Reviews of Past Studies

A 2013 study published in the Korean Journal of Family Medicine reviewed past studies investigating the benefits of probiotics for preventing the common cold.

The authors selected 10 studies involving almost 3,000 participants. The results of their review showed that probiotics provided a modest but significant effect on the reduction of the common cold. In their opinion, probiotics were effective with or without vitamins and minerals.

In addition, they found probiotics more effective when taken for longer than 3 months.

A 2011 review from The Cochrane Collaboration analyzed available evidence to determine whether probiotics can help prevent respiratory infections.

By taking data from 14 randomized controlled trials involving 3,451 participants, they found that probiotics were effective for reducing the number of upper respiratory tract infections (cold and the flu, etc.) experienced as well as antibiotic use and duration of the infections.

Lastly, the authors found that probiotics only caused minor gastrointestinal symptoms and were largely safe for consumption.

Probiotics vs. Influenza A Virus

A lot of studies investigating the effect of probiotics conclude that they confer their benefits on health by boosting the immune system. However, this study published in the journal, Scientific Reports, in 2003 indicated that probiotics may have a direct antiviral effect against the influenza virus.

In the study, the researchers introduced heat-killed Lactobacillus pentosus b240 into a mouse model infected with the influenza A virus (H1N1).

Although their study did not show that the probiotic affected the replication of the virus and cytokine production, it showed that the probiotic regulated gene expression in the influenza viruses found in the lung of the mouse.

This result is important because it demonstrates that probiotics may disarm cold and flu viruses without necessarily killing them off.

The task of destroying the viruses rests with immune cells such as leucocytes and NK cells.

In addition, the results showed that this inhibition of the influenza virus occurred in the lungs. This shows that the antiviral effect of probiotics occurs in the respiratory tract, the very organ-system most affected by cold and flu.

With or Without Vaccination

Vaccination is officially considered the best means for preventing flu during the winter months. However, probiotics also boost the immune system and may offer a comparable level of protection.

A 2010 study published in The Journal of Alternative and Complementary Medicine investigated the effectiveness of a probiotic yeast for cold/flu-like symptoms in a group of people who did not receive flu shots. For this study, the researcher recruited 112 volunteers.

Then over a period of 12 weeks, they gave some of them a once-daily 500 mg dose of dried modified Saccharomyces cerevisiae oral fermentate (EpiCor) while the others got a placebo.

The results of the study showed that, compared to the placebo group, the probiotic yeast reduced the incidence of colds or flu-like symptoms but not their duration or severity. In their conclusion, the researchers believed that this probiotic was a safe and effective alternative to flu vaccines for protecting against cold and flu-like symptoms of seasonal flu.

A 2012 study published in the British Journal of Nutrition also examined the relationship between flu vaccines and probiotics but from a different angle.

In this study, the researchers investigated the effects of probiotics on the performance of flu vaccines.

The researchers recruited 211 subjects and divided them into 3 groups. While one group received a placebo, the second group received probiotic capsules containing Bifidobacterium animalis subsp lactis while the third group got Lactobacillus paracasei in the form of a dairy drink.

While the treatment went on for 6 weeks, all the volunteers were given seasonal influenza vaccination after 2 weeks.

The results showed that both probiotic groups had higher plasma levels of flu vaccine-specific immunoglobulins, IgG, IgG1, and IgG3. In addition, total antibody levels and saliva IgA levels were higher in the probiotic groups than the placebo group.

The researchers concluded that the 2 probiotics used boosted systemic and mucosal immune response to the influenza virus challenge.

This study indicates that probiotics can improve the efficacy of flu shots and confer greater protection against influenza viruses during the flu season. However, the right probiotics should be selected. The ones used in this study are the most effective probiotics for preventing and/or treating colds and flu.

The Right Probiotics for Cold and Flu
  • Lactobacillus acidophilus
  • Lactobacillus casei
  • Lactobacillus paracasei
  • Lactobacillus plantarum
  • Lactobacillus gasseri
  • Lactobacillus pentosus
  • Bifidobacterium animalis subsp lactis
  • Bifidobacterium longum
  • Bifidobacterium bifidus





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