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.

Colds and Flu

Beating Colds and Flu

Most of us suffer from colds year round. Here’s a way to bolster your chances of staying healthy this season.

This episode features audio from Boosting Immunity Through Diet, Preventing the Common Cold With Probiotics?Kiwifruit for the Common Cold, and Can Gargling Prevent the Common Cold?.


Hello and welcome to Nutrition Facts – the podcast that brings you the latest in evidence-based nutrition research.  I’m your host, Dr. Michael Greger.

I know that facts have been in the news a lot lately, both real and fake.  The concept of alternative facts is nothing new in the field of nutrition, though, where powerful commercial interests have tried to not only keep people in the dark, but actively try to confuse them.  That’s why I stick to the science:  What’s the best available balance of evidence published in peer-reviewed medical journals right now?    That’s why I wrote my New York Times best-selling book, “How Not to Die” and why I created my nonprofit site NutritionFacts.org and, now, this podcast.

Though flu and cold season only comes around once a year, people can suffer from upper respiratory tract infections year round and, today, we’re going to look at ways to prevent and treat them. 

Inadequate fruit and vegetable intake may help explain the loss of immune function as we age, which is linked to an increased risk of dying from pneumonia and influenza.  Here’s the story. 

Recently, researchers in Belfast reported an investigation into the possibility that inadequate diet may be a contributing factor to immunological aging.  Both immunity and fruit and vegetable intake can be low in the elderly, so they wondered if there might be a connection.

So, they rounded up 83 volunteers between 65 and 95 years of age and randomized them into the control group, following their pitiful two or fewer servings of fruits and vegetables a day diet, versus the experimental group that were told to consume at least five.  They did this for a month before they were due for their pneumonia vaccine. The experimental group didn’t quite hit five daily servings, but at least they did better than control group.

Here’s what happened when they were given Pneumovax.  Here’s the immune response in the control group:  They were injected with pneumonia bacteria vaccine.  Their immune systems should have gone crazy making antibodies to fight off the perceived invader and, they tried their best, but this is the group that was on almost five servings of fruits and veggies every day for the prior four weeks.

Influenza and pneumonia constitute the seventh leading cause of death for our elderly.  It’s never too late to start eating healthier.

We’ve been hearing a lot about probiotics lately.  Here’s some information about the different ways that they can reduce the risk of upper respiratory tract infections.

Babies delivered via Caesarean section appear to be at increased increase for various allergic diseases.  The thought is that vaginal delivery leads to the first colonization of the gut with maternal vaginal bacteria, while C-section babies are deprived of this natural exposure and exhibit a different gut flora.  This is supported by research noting that a disturbance in maternal vaginal flora during pregnancy may be associated with early asthma in their children.  This all suggests our natural gut flora can affect the development of our immune system, for better or for worse.

In adulthood, two studies published back in 2001 suggested that probiotics could have systemic immunity-enhancing effects.  Subjects were given a probiotic regimen between weeks three to six and saw a significant boost in the ability of their white blood cells to chomp down on potential invaders and, what’s interesting is that even after the probiotics were stopped, there was still enhanced immune function a few weeks later compared to baseline.  The same boost was found in the ability of their natural killer cells to kill cancer cells and similar results were also found using a different probiotic strain.

Now, improving immune cell function in a Petri dish is nice, but does this actually translate into people having fewer infections?  For that, we had to wait another ten years but, now, we have randomized, double-blind, placebo-controlled studies showing that those taking probiotics may have significantly fewer colds, fewer sick days, and fewer symptoms.

The latest review of the best studies to date found that probiotics, such as those in yogurt, soy yogurt, or supplements, may indeed reduce one’s risk of upper respiratory tract infection but, the totality of evidence is still considered weak, so it’s probably too early to make a blanket recommendation.

Unless one has suffered a major disruption of gut flora by antibiotics, or an intestinal infection, unless one is symptomatic with, like, diarrhea, or bloating, I would suggest focusing on feeding the good bacteria we already have by eating so-called prebiotics, such as fiber.

After all, as we saw before, who knows what you’re getting when you buy probiotics?  They may not even be alive by the time you buy them.  They also have to survive the journey down to the large intestine.  Altogether, these points suggest that the advantages of prebiotics found in plant foods outweigh those of probiotics and by eating raw fruits and vegetables, we may be getting both.  Fruits and vegetables are covered with millions of lactic acid bacteria, some of which are the same type used as probiotics.  So, when studies show eating more fruits and vegetables boosts immunity, prebiotics and probiotics may both be playing a role.

I’ve got a question for you:  Compared to bananas, does eating kiwifruit decrease the incidence and severity of upper respiratory tract infections?  Let’s take a look at the facts.

It is well known that deficiencies in certain vitamins and minerals can lead to significant impairment of immune function and an increased susceptibility to infection, which can be reversed by supplementation in deficient individuals; however, it is unclear to what extent supplementation may aid in maintaining an optimal balance within the immune system in adequately nourished individuals.  So, researchers in New Zealand tried supplementing with kiwifruit.  In a Petri dish, gold kiwifruit puree appeared to boost natural killer cell activity in human blood and boost the response to a tetanus vaccine, but does, you know, what happens in a Petri dish happen in people?

There was a study in which two immune-related sets of genes were found to be upregulated by eating three kiwifruit a day.  But, does this translate into actual helping us fight off infection?  We didn’t know, until this study.

Researchers in New Zealand found that the consumption of gold kiwifruit reduces the severity and duration of certain upper respiratory tract infection symptoms.  Why study gold kiwifruits?  Because the study was funded by the company that owns the patent to gold kiwifruits.  A few dozen elderly individuals were randomized to one or two groups, eating two bananas a day, or eating four kiwifruit a day for a month, and then they switched.  The next month, the banana group ate kiwis and the kiwifruit group ate bananas.

The rationale for providing banana as kind of like the placebo was to provide an alternative fruit that had relatively similar calories, but lower nutritional value.

The purpose of the study was to determine whether regular consumption of gold kiwifruit reduces the incidence, duration, and severity of symptoms of upper respiratory tract infections, like the common cold, in comparison to bananas.  They found no reduction in overall incidence, but those that did get sick during the kiwifruit phase had significantly reduced severity and duration of head congestion and the duration of sore throat–and not just by a little.  The sick banana eaters suffered for five days with a sore throat and congestion, compared to the kiwifruit eaters, who felt better after just a day or two.  That’s significant!

The reason they studied older individuals is that they tend to be more susceptible to respiratory infections.  Small children are another at-risk group, averaging twice as many upper respiratory tract infections as adults (four to six a year).  So, 66 preschoolers were randomized into the same two groups, kiwifruit versus bananas, and not only were there, again, significant improvements in the symptoms of those who got sick while on kiwifruit, fewer got sick in the first place.  Forty-five percent lower odds of a cold or flu-like illness, which means that the children eating kiwis had almost a 50% reduction in the chance of having a cold or flu.

This suggests that kiwifruit consumption may be a daily prescription for health, though, about 1 in 150 children report being allergic to kiwifruit, which ranks them #3 after milk and eggs, and above peanuts, in a survey of 3,500 kids, as the most common food allergies and, so, are not for everyone.

Gargling, as commonly practiced in Japan, cannot only soothe a sore throat, but may even help prevent one.  Here’s the story.

Gargling is one of the best things to do to treat a sore throat.  As one of my medical mentors, Dr. Michael Klaper, instructs, you take a glass of warm water, add a pinch of salt, hold the glass of salt water in your hand, open your mouth, take a deep breath, tilt your head back, slide a generous mouthful to the back of your throat and, with your mouth still open, gently breathe out through the water.  Continue until the end of the breath and then spit it out into the sink.  Repeat until the full glass of salt water is used.  Works wonders to soothe a sore throat when you have a cold, but I never heard of gargling to prevent a cold.  

Though not popular in the Western world, gargling has been strongly recommended in Japan to prevent upper respiratory tract infections, such as the common cold; however, there had been no controlled trials and it remained unresolved as to whether gargling was really effective—until this one was published in 2005.  They found a significant drop in the incidence of the common cold, but not the flu, suggesting that simple plain water gargling is effective in preventing upper respiratory tract infections among healthy people.  This virtually cost-free modality would appreciably benefit people both physically and economically around the world.

What do they mean, economically?  Well, most Americans, for example, report about two to three colds a year.  That actually surprised me.  Between medical costs and work absenteeism, we’re talking nearly 40 billion dollars a year–the common cold.  So, even if you take into account the 71 seconds it took, on average, to walk to and from the sink, and gargle, and multiply that by the average wage to calculate the cost of gargling in wasted time, it’s still considered a cost-effective strategy.

Here’s the latest; a new study on whether it works in kids:  Gargling for Oral Hygiene and the Development of Fever in Childhood.  A total of nearly 20,000 preschoolers were observed for 20 days and, just like the study for adults, gargling appears to lower the odds of illness by about a third and, gargling with green tea may work better.  Note, they speculate that the fact that tap water is chlorinated may have played a role.  So, gargling with filtered water may be less effective. But, I would stay away from iodine solutions (such as Betadine), since one can run into the same kind of iodine overload thyroid dysfunction you can get by eating too much kelp.

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 the sources we cite for each of these topics.

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.

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