Boost your good gut bacteria with probiotics in order to enhance your immune function, and help fight off inflammation and infection.

Thanks to the pandemic, as well as cold and flu season, we are reminded that eating to enhance the immune system is a hot trend. Sauntering down the supermarket aisle, you will surely spot a variety of food products—from cookies to juices—boasting immune health benefits. In fact, food industry insiders consider immune support a new functional food niche. MarketWatch reported in March 2019 that the global probiotics market is anticipated to reach over $77 million by 2026, referencing consumer awareness of the health benefits offered, such as improved digestion, stronger immune system, healthier skin, and decreased chances of cold and flu. According to a September 2019 issue of Nutraceuticals World, there was a 72% rise in food and drink launches featuring probiotics in 2018. They report other reasons behind consumer interest, among them are an increasingly polluted world, hard-to-kill microbes, concerns about the pandemic, more stress due to work and family responsibilities, and a reliance on highly processed foods that may potentially compromise a person’s immune system and increase risk of illness.

As healthcare costs rise, maintaining a strong immune system provides tangible value for many people. Mothers are always on the lookout for ways to help their children avoid catching the latest bug. Boomers are determined to live active lifestyles as they age, searching for preventive methods to maintain their health. According to the Natural Marketing Institute’s Health and Wellness Trends Report, people believe that maintaining good immune health is the best way to prevent illness. The increased interest in eating for immune health is a good thing, since infectious diseases are the world’s leading cause of morbidity.

But just how much science is there to support probiotics’ role in improving immune health?

Good Gut Bacteria Boost Immune Health
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Gut’s Role in Immune Function 

The immune system, the body’s protective network that fends off the invasion of harmful substances such as bacteria, viruses, and chemicals and guards against the development of cancer, allows humans to flourish in a busy, interactive world. Multiple barriers protect against foreign invaders, including the skin, inflammatory responses, and specific immune responses, such as certain types of immune cells like natural killer cells and macrophages that destroy pathogens.

One key player in immune health is the gut, a part of the body that is constantly exposed to toxins and foreign antigens, such as those from food and microbes. According to nutrition and immune expert Simin Meydani, DVM, PhD, director of the Jean Mayer USDA Human Nutrition Research Center on Aging and the Nutritional Immunology Laboratory at Tufts University, “The gut is the largest immune organ in the body, accounting for 25% of the immune cells in the body that provide 50% of the body’s immune response. There are more than 400 species of bacteria residing in the gut, and they have symbiotic relationships with your body.”

Meydani calls the gut flora “the forgotten body organ” because of its vital yet underappreciated health functions. “There are 100 trillion bacteria in our intestines. The assembly of intestinal bacteria is called the intestinal flora. They form an ecosystem like a flower garden,” reports Haruji Sawada, formerly the director of the Yakult Central Institute in Japan. In fact, there are 10 times more intestinal bacteria than there are human cells in the body. Humans develop their intestinal flora after birth, not in the womb. Thus, newborn babies’ gastrointestinal tracts are sterile but quickly become colonized by microorganisms after birth. During babies’ first year of life, the intestinal microbiota begin to develop to resemble that of an adult.

The current knowledge base on intestinal flora is expanding. “It’s pretty clear that the microbes in your body are an important part of the development and function of the immune system. Microbes have evolved mechanisms to communicate with immune cells, and our bodies communicate with microbes,” says Mary Ellen Sanders, PhD, a consultant on probiotics for the food and supplement industry. Scientists know that intestinal microbiota may aid in the maturing of immune cells and physically block the passage of pathogenic bacteria and antigenic components of foods.

Sawada explains that intestinal bacteria are separated into good (beneficial), opportunistic, and bad categories. Beneficial bacteria, such as Bifidobacteria or Lactobacilli, help maintain health by resisting bad bacteria and harmful substances and aiding digestion and nutrient absorption. Opportunistic bacteria such as Enterobacteria take advantage of certain conditions to cause disease. And bad bacteria such as Staphylococcus and Clostridium cause disease because they produce toxins or are carcinogens.

“Factors influencing the intestinal flora include an unbalanced diet, stress, fatigue, aging, antibiotic therapy, and bacteria-contaminated food,” says Sawada. “These conditions increase the levels of harmful bacteria in the intestines.”

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Science on Probiotics and Immune Health

Looking to probiotics to support immune health is nothing new; the idea has existed for more than 100 years. Probiotics’ main benefit is that they help restore balance in the intestinal microbiota. “Probiotics are live microorganisms that beneficially affect the host by improving the intestinal flora,” says Sawada.

Scientific evidence is now emerging to further support probiotics’ role in immune health. “There are mechanistic studies that show when you consume a probiotic, it can interact with different immune cells and lead to potentially positive changes,” says Sanders. Tetsuji Hori, formerly the Yakult USA science manager, reports that while there are other mechanisms involved in probiotics’ immune benefits, natural killer cell, a lymphocyte that functions in the rejection of tumor cells and cells infected by viruses, is of particular interest. He reports that research indicates the probiotic Lactobacillus casei Shirota (LcS) augments natural killer cell activity.

“A growing number of studies show that probiotics can help healthy subjects stay healthy,” says Sanders. “For example, studies have shown that children in day care centers don’t get sick as often when they consume probiotics. If you combine the mechanistic studies with the studies showing fewer respiratory and GI infections, it suggests that the immune effects are meaningful.”

Sanders reports that there are several examples of probiotics with scientific evidence supporting immune health benefits, including Lactobacillus casei DN-114 001 (DanActive), Lactobacillus reuteri ATCC 55730 (BioGaia Probiotic drops), Lactobacillus rhamnosus GG (Culturelle), and LcS (Yakult). The following are several examples of studies that show the immune benefits of probiotics among healthy subjects:

  • A 2019 review of studies on probiotic supplementation in healthy adults reported that probiotic supplements have a positive impact on several health outcomes, including: improvement in gut microbiota concentration of supplement-specific bacteria, immune system responses, stool consistency, bowel movement, and vaginal lactobacilli concentration.
  • Reported in Immunity and Ageing in December 2015, a randomized, double-blind, placebo-controlled parallel-arms study was performed on 100 healthy subjects aged 60-74 to assess the effects of Bacillus subtilis CU1 consumption on immune stimulation and resistance to common infectious disease. Subjects consumed either the probiotic or placebo for 10 days, alternating every 18 days four times total over four months. Consumption of the probiotic significantly increased immune response compared to placebo.
  • Researchers studied the influence of prebiotics, probiotics, and synbiotics on health and mucosal and immune function by altering the composition of gut microbiota in a study in the June 2014 British Journal of Nutrition. All three were given to healthy adults aged 25-65 years for 21 days. The probiotic significantly increased in the gut and lowered inflammatory secretions in blood cultures and saliva content. The lowest use of pain killers was reported during the symbiotic period.
  • A study in the December 2013 European Journal of Nutrition reported on probiotics’ health benefits by modulating immune function. Thirty healthy volunteers participated in a randomized, placebo-controlled, single-blind crossover study. They drank either a probiotic drink or skimmed milk daily for four weeks, followed by four weeks break, and then did the opposite for four more weeks. Drinking the probiotic drink was associated with increased the activity of antitumor cells and tended to produce a more anti-inflammatory profile in older people.

While the research is building in support of immune-protection benefits in general populations, there is also much to consider in treating special conditions or groups of people. For example, Koji Nomoto, PhD, chief researcher of the Yakult Central Institute, reports on the effects of the preoperative oral administration of synbiotics (prebiotics and probiotics) in patients with biliary cancer who were undergoing high-risk hepatobiliary resection. The study found that the preoperative oral administration of synbiotics enhanced immune responses, attenuated systemic postoperative inflammatory responses, and improved intestinal microbial environment. Such benefits may reduce postoperative infectious complications after hepatobiliary resection for biliary tract cancer.

Bottom Line Recommendations 

Just because science suggests that probiotics may support immune health doesn’t mean every product on the market offers the same advantages. “It’s important to remember that probiotic benefits are strain specific, dose specific, and maybe even matrix specific. For example, probiotics in capsules may have different effects than probiotics in yogurt. Also remember that not all products in the marketplace called ‘probiotic’ have solid science backing them,” stresses Sanders.

Indeed, there are scores of probiotic products available, and they’ve moved beyond fermented dairy products such as yogurt and kefir; today, dietary supplements and products such as frozen yogurt, cereal, juice, and cookies claim to contain probiotics. To complicate matters, consumers are easily confused by probiotics. This complex concept involves good and bad bacteria as well as a slew of complicated scientific terms about the immune system. And whether a particular probiotic product contains adequate amounts of efficacious probiotic strains is another matter.

“My strongest recommendation is to use probiotics with good-quality evidence behind them. But it can be hard to see benefits with immune health in consumers who are generally healthy anyway. Since there is a good history of safety with probiotics from genera such as Lactobacillus and Bifidobacterium, I don’t see anything wrong with people trying products out to see if they work for them,” advises Sanders. “If consumers choose probiotics in foods, they may see a reduction in being sick with GI or upper respiratory illnesses, and they can also benefit from the nutrients in the product, such as calcium and protein in yogurt. When it comes to specific applications in certain illnesses, such as immune-suppressed individuals, the science is emerging, so stay tuned. Be familiar with the research and look at the quality of the studies.”

Good Advice on Probiotics 

  • Not all probiotics are created equal. Different strains of even the same species can be different and may not produce the same effects. A probiotic is defined by its genus (eg, Lactobacillus), species (eg, rhamnosus), and strain designation (often a combination of letters or numbers).
  • Trademarked names, often used by manufacturers for marketing purposes, are essentially an alias for the probiotic strain.
  • Whether probiotics are found in foods or supplements, the content of the probiotic is generally more important than the way in which it is consumed.
  • Probiotics sold as dietary supplements or food ingredients cannot legally claim to cure, treat, or prevent disease, but claims that relate the product to health are allowable.
  • Ensure that sound science backs probiotics using the term “clinically proven” on their label and ensure that the products contain the specific strain(s) of bacteria at the same levels as those used in published research. The studies should be performed in humans and published in reputable peer-reviewed journals.
  • Just because a product says “probiotic” doesn’t mean it is a probiotic. Some products do not have clinically validated strains or levels.
  • Discuss their use of probiotics with a physician, and warnings of side effects or symptoms should be reviewed.
  • Look for the right quantity of probiotics, which are measured in colony-forming units (CFUs), the measure of live microbes in a probiotic. The CFUamount should be the same as that shown to be effective in clinical studies. Different probiotics have been shown to be effective at different levels; thus, it’s impossible to provide one count for all probiotics.
  • Pick a product from a trusted manufacturer, who is more likely to ensure that the probiotic product has the same strain(s) and is as potent through the end of shelf life as what was used in clinical studies.
  • The product label should reveal the following: strain, CFUs, expiration date, suggested serving size, health benefits, proper storage conditions, and corporate contact information.

To read more about gut health and diet, check out these blogs:

Eat These Foods for Gut Health
5 Expert Tips to Boost Your Gut Bacteria
Learning All About Probiotics

Image: Plant-based yogurt, Sharon Palmer

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