Have you ever wondered if there’s a natural way to lower your high blood pressure, guard against Alzheimer's, lose weight, and feel better? Well as it turns out there is. Michael Greger, M.D. FACLM, founder of NutritionFacts.org, and author of the instant New York Times bestseller “How Not to Die” celebrates evidence-based nutrition to add years to our life and life to our years.

Improving Immune Function

If you want to help your body defend itself against invaders that attack your immune system, you’ll want to take a listen.

This episode features audio from Best Food to Counter Stress-Induced Immune Suppression, Preserving Athlete Immunity with Chlorella, and Preserving Immune Function in Athletes with Nutritional Yeast. Visit the video pages for all sources and doctor’s notes related to this podcast.


There are lots of good reasons to try and follow a healthier diet–you lose weight, you feel good, but the main reason–to live a longer, happy, productive life.  Sounds good, right?   And though it may sound deceptively easy, the devil is in the details.   Welcome to the Nutrition Facts podcast.  I’m your host, Dr. Michael Greger. 

Today, we talk about improving how our body defends itself against invaders.  And if that sounds like a video game – well, that’s not too far from the truth, because our bodies are constantly under attack. Here are some ways to improve immune function in children and adults under physical or psychological stress.

“Natural immunomodulators are getting more and more popular [things that might naturally regulate our immune system]. That popularity, however, often brings over-optimistic claims and mediocre effects.” Such mythical beasts “have been sought [after] for centuries. The current market is full [of all sorts of supplements] promising the golden fleece–inexpensive,” no side effects, yet actively boosting our immune system. Many simply repeat unjustified claims “with hardly any” science to support them.

On the other hand, there is beta-glucan, which has “undergone…10,000 scientific studies…and…clinical trials. Wait, what? Beta-glucan is the fiber in nutritional yeast—able to decrease episodes of common illnesses in young children. But what about in adults?

First of all, why can’t they just come up with a vaccine against the common-cold virus? Because there is no single common-cold virus; there are hundreds of different viruses implicated in causing cold-like symptoms. So, that’s why there’s so much interest in finding a general, nonspecific immune booster, across the board.

Beta-glucan supplementation can increase the levels of immunoglobulin A in the saliva within four days, at a daily dose of 400 mg, but not 100 mg. So, the amount found in about two teaspoons of nutritional yeast a day; but not a half-teaspoon. (IgA is an antibody that plays a crucial role in the immune function of our moist membranes, like eyes, nose, and mouth.) One teaspoon’s worth didn’t do much, until they exercised.

Two hours after a strenuous 50-minute bout of strenuous cycling in a hot, humid environment, those who had been on the yeast beta-glucan did get that IgA boost. Beta-glucans failed, however, to boost the antimicrobial activity of white blood cells taken from subjects who had been taking like a tablespoon’s worth a day. What we care about, though, are clinical outcomes.  Do those consuming beta-glucans suffer significantly fewer infections?

Okay. How about a double-blind, randomized, placebo-controlled nutritional study to see if yeast beta-glucan can improve our “immune defense system.” A hundred people followed for 26 weeks; 50 getting about a tablespoon of nutritional yeast worth of beta-glucan a day; 50 getting a placebo. And they just counted how many episodes of the common cold they got, and there was “no significant difference.” Now, if you just look at the first half of the time, during cold season, there did appear to be fewer infections in the active group, meaning the beta-glucan group. But, this is what’s called a “post-hoc” analysis, where you go back and look at your data after the fact—which is frowned upon by the scientific community, because it increases the likelihood that your findings are just due to chance. But, those who did end up getting sick while on the beta-glucan did genuinely appear to suffer milder symptoms. A similar, larger study had similar findings. Maybe the severity of the colds was lessened, but, in the main analysis, no significant difference in the number of times people got colds in the first place.

Same in other studies: “no significant differences…in the number of [symptomatic respiratory infection] episodes.” No significant effect on upper respiratory tract infection outcomes. So, overall, pretty disappointing results.

But, wait a second. What about my video about preserving immune function in athletes with nutritional yeast? They found a significant drop in cold symptoms two weeks and four weeks after a marathon at both one teaspoon of yeast worth of beta-glucan a day, and two teaspoons. Yeah, but they had just run a marathon. Remember this study, where the effect only seemed to emerge after strenuous exercise? That’s where beta-glucan seems to shine: counteracting the toll extreme physical exertion can have on our immune function.

In an athlete, that just may mean some lost practice days or something, but for soldiers or firefighters, maintaining one’s health, even in the context of heavy physical stress, could be critical. Okay. But, that’s counteracting the effects of physical stress; what about mental stress?

Stressful life events can impair our moist membrane defenses, such that “psychological stress [has also] been shown to increase susceptibility to the common cold,” getting more colds, and worse colds, than people under less stress. So, let’s see if we can help and, indeed, in this study of healthy women under moderate levels of perceived psychological stress, those taking about a teaspoon of nutritional yeast a day worth of beta-glucans for 12 weeks were 60% less likely to report experiencing symptoms, like sore throat, stuffed or runny nose, or cough—strongly suggesting that baker’s, brewer’s, and nutritional yeast “beta-glucan is able to counteract the negative effects of stress on the immune system.” And, they experienced 41% greater vigor (which is a measure that encompasses “physical energy, mental acuity, and emotional well-being”). So, they just felt better, too.

Put all the studies together, and yeast beta-glucans do appear to have immune-strengthening effects, at least in children, and those under physical or mental stress.

The green algae, chlorella, may help attenuate the drop in immune function antibodies associated with over-strenuous exercise.  Here’s the research.

Sedentary women who start briskly walking on a treadmill 45 minutes a day for a few months may cut their risk of upper respiratory tract infections in half. But how does exercise improve our immune system?

Approximately 95% of all infections are initiated at the mucosal surfaces—the moist surfaces, like our eyes, nose, and mouth, that are protected by antibodies like IgA, which provides an immunological barrier by neutralizing and preventing viral pathogens from penetrating the body. The IgA in our saliva, for example, is the first line of defense against respiratory tract infections such as pneumonia and influenza.

And moderate aerobic exercise, even just 30 minutes in the gym three times a week, may be all it takes to significantly boost IgA levels and significantly decrease the risk of coming down with flu-like symptoms.

But we’ve known for a long time that prolonged heavy exercise may reduce resistance to infectious disease, manifesting by an apparent two- to six-fold increase in upper respiratory tract infection symptoms for several weeks following marathon running.

Even just a single bout of over strenuous exercise may drop IgA levels. Within a day of starting an international competition, for example, elite soccer players suffered a significant drop in IgA secretion. Yacht racing athletes training for America’s Cup who got upper respiratory tract infections during training had significantly lower IgA concentrations. Those with higher levels had fewer infections, and if you measure over time, you can see dropping levels precede the infection. Furthermore, a simple fatigue rating appears to reflect changes in salivary immunity. If you just ask them, “How rested do you feel?” those who reported feeling worse than normal had significantly lower IgA levels.

Sport coaches are advised to monitor immune function, since illness could ultimately lead to a decrease in performance. Therefore, it may be necessary to take protective actions to, for example, minimize contact with cold viruses. But the reason athletes can’t get away with just washing their hands and wearing a mask is because upper respiratory tract infections are often triggered by reactivations of latent viruses already inside our bodies, like Epstein-Barr virus (EBV), and as soon as our immune function dips, the virus becomes reactivated. IgA levels drop the day before EBV comes out of hiding and causes a spike in symptoms. These results suggest that the appearance of upper respiratory symptoms is associated with reactivation of EBV and reduction of salivary IgA during training.

So, how are we going to preserve immunity in athletes? Well, I talked about the efficacy of using a one-celled fungi—nutritional yeast—to boost the immune systems of athletes.  What about a one-celled plant?

Researchers out of Japan found IgA concentrations in breast milk could be increased by giving mothers chlorella, a unicellular freshwater green algae sold as powder or compressed into tablets. What about other parts of the body? Thirty tablets of chlorella a day for a month increased IgA secretion in the mouth as well. But does that actually help in a clinically meaningful way? Researchers in Canada tried to see if they could boost the efficacy of flu shots, but a chlorella-derived dietary supplement did not appear to have any effect. They were using some purified extract of chlorella, though, not the real thing.

What about giving chlorella to athletes during training camp? High-intensity physical activity, group living—ripe for infection, and indeed the training was so intense IgA levels significantly dropped, but not in those given chlorella each day. So, chlorella intake may attenuate the reduced IgA secretion during athletic training.

Athletes who overtrain may put excessive stress on their bodies, and become more susceptible to respiratory infections. But, the fiber found in nutritional and brewer’s yeast may prevent this immune decline in marathon runners.

“Moderate exercise improves immunity and decreases illness rates. By far, the most important finding that has emerged from exercise immunology studies [during] the past 2 decades is that positive immune changes take place during each bout of moderate physical activity.” Over time, this translates to fewer days of sickness with the common cold and other [upper respiratory infections].” We’re talking a “25% to 50% reduction in sick days.” Name one drug or supplement that can do that!

And, it doesn’t take much. Let kids run around for just six minutes, and you can boost the numbers of immune cells circulating in their bloodstream by more than a third.

At the other end of the life cycle, exercise may help prevent age-related immune decline. Sedentary women in their 70s may have a 50% chance of getting an upper respiratory illness during the fall season every year, but walk a half-hour a day, and your risk is down to 20%. And the runners in the group got it under 10. That’s like a five times better immune system.

Now, while “[r]egular physical activity improves immune function and lowers [upper respiratory infection] risk,…sustained and intense exertion [may have] the opposite effect”—forming a so-called J-shaped curve relationship. As you go from inactive to active, your infection risk declines, but hardcore athletes that overtrain may actually put excessive stress on their bodies, and increase their risk of infection. Then, you could lose training days; your performance could suffer. So, what can you do? Well, traditional sports medicine doesn’t appear to have much to offer, advising athletes to you know, don’t pick your nose, avoid sick people, and get a flu shot.

A new study, though, found that one can better maintain one’s level of circulating white blood cells after exhaustive exercise by consuming a special type of fiber found in baker’s, brewer’s and nutritional yeast. Brewer’s yeast is bitter, but nutritional yeast has a nice cheesy flavor. I use it mostly to sprinkle on popcorn. Anyway, normally two hours after cycling-your-brains-out, you can experience a dip in circulating monocytes—one of our first line of defense white blood cells. But, those who had been eating the equivalent of less than 3/4 of a teaspoon a day of nutritional yeast ended up even better than when they started, after strenuous exercise.  Sprinkle a little spoonful of nutritional yeast, and you may feel less tense, less fatigued, less confused—even less angry, and my favorite, significantly more vigor!

To see any graphs, charts, graphics, images or studies mentioned here, please go to the Nutrition Facts podcast landing page.  There, you’ll find all the detailed information you need, plus links to all of the sources we cite for each of these topics.

Be sure to check out my new How Not to Die Cookbook. It’s beautifully designed, with more than 120 recipes for delicious, plant-based meals, snacks, and beverages. All the proceeds from the sales of all my books all go to charity. I just want you to be healthier. 

NutritionFacts.org is a nonprofit, science-based public service, where you can sign up for free daily updates on the latest in nutrition research via bite-sized videos and articles.

Everything on the website is free. There’s no ads, no corporate sponsorship. It’s strictly non-commercial. I’m not selling anything. I just put it up as a public service, as a labor of love—as a tribute to my grandmother – whose own life was saved with evidence-based nutrition.

Thanks for listening to Nutrition Facts. I’m Dr. Michael Greger.

This is just an approximation of the audio content, contributed by Allyson Burnett.


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