Full transcript
0:01We have lots of choices to make about
0:03our diet and to that doing the right
0:06thing when it comes to treating a
0:07chronic disease or fighting a virus or
0:10losing weight and suddenly
0:12our nutrition choices can seem almost
0:15overwhelming. Well,
0:17I'm here to help. Welcome to the
0:19NutritionFacts podcast. I'm your host
0:21Dr. Michael Greger. Today we look at the
0:23different ways we can improve immune
0:26function and we start with one that
0:28might surprise you.
0:30>> Several studies have demonstrated that
0:32cold temperatures may be a potential
0:33risk factor for cancer development. For
0:36example, this study compared the 50
0:38countries with the highest cancer rates
0:40to the countries with the lowest cancer
0:42rates and conclude that people living in
0:44cold environments may have a higher risk
0:47of getting and dying from cancer.
0:50A similar study within the United States
0:51found that colder counties were
0:53associated with a greater cancer
0:55incidence.
0:56But couldn't something like vitamin D
0:58exposure better explain these findings?
1:00Patients diagnosed with cancer during
1:02summer months may have a better
1:03prognosis than those diagnosed during
1:05the winter, but again this could be
1:07because of the sunshine vitamin, vitamin
1:09D. Evidently an animal colony had less
1:12cancer when they moved from a colder
1:13country to a warmer country based on
1:15some observation published in 1939. That
1:19seems a bit of a stretch. But then this
1:22study was published.
1:24Standard housing temperatures for
1:26laboratory mice in research facilities
1:28is mandated to be between 20 and 26°C
1:32unlike typical room temperatures in the
1:3470s Fahrenheit.
1:36But that's chilly for mice causing
1:39chronic mild cold stress. When that
1:41stress is alleviated by housing at
1:43warmer temperatures like in the 80s
1:45Fahrenheit, researchers observed a
1:47striking reduction in tumor formation,
1:50cancer growth rate, and metastasis.
1:52Warmer was better.
1:54They They that the cold stress results
1:57in a suppression of anti-tumor immunity.
2:00Then why do they keep mice at that lower
2:03temperature?
2:04It reduces the frequency of cage
2:06cleaning and helps ensure the thermal
2:09comfort of the staff.
2:11The proposed mechanism is the activation
2:13of the fight or flight response at least
2:15through the release of the stress
2:16hormone norepinephrine, also known as
2:18noradrenaline.
2:20Take a dip in a typical cold plunge and
2:22there can be a doubling of
2:23norepinephrine levels in the blood
2:25within minutes. And we don't seem to
2:26habituate, meaning we get that same bump
2:29in norepinephrine after each cold water
2:31immersion, even after 3 months of
2:33regular plunges.
2:35Might that be suppressing immune
2:37function? Or might it instead be
2:40hormesis, that which doesn't kill us
2:42makes us stronger?
2:44Cold water swimmers claim to suffer
2:46fewer and milder infections as a result
2:49of the practice.
2:50Even if that's true, cold water swimmers
2:53are swimming. Maybe it's the exercise,
2:55not the cold. How would we figure this
2:58out?
3:00To control for any effect of swimming,
3:02researchers compared cold water swimmers
3:04to indoor heated pool swimmers and
3:08found no difference in upper respiratory
3:10tract susceptibility between swimmers in
3:12cold water and heated pools. Therefore,
3:15cold water swimming appears to have no
3:16protective effect.
3:19What about regularly taking cold
3:21showers? Cold showers were first
3:23designed for the purpose of {quote}
3:25treating the insane and then used as an
3:28instrument of torture in prisons before
3:31it started killing too many people.
3:34Rather than being abandoned, however,
3:36the shower was transformed by the use of
3:38warm water to actually clean people. No
3:40idea.
3:41If you randomize people to short daily
3:43cold showers versus hot showers for a
3:45few months, regular cold shower exposure
3:48does appear to put the immune system on
3:50high alert. Does that actually translate
3:52into less sickness? There's only been
3:54this one randomized trial on the effect
3:56of cold showering on health and work, a
3:58randomized controlled trial.
4:00Participants were randomized to shower
4:02as normal, but end their showers with 0,
4:0530, 60, or 90 seconds of cold water.
4:08And compared to the no cold group, the
4:11different cold water groups collectively
4:13had a 29% reduction of self-reported
4:15sick leave from work, but no fewer
4:17self-reported days of sickness.
4:20Uh so, maybe the cold showering made
4:22them less sick even though they were
4:24sick for the same duration.
4:26The [clears throat] problem, of course,
4:27is that while there was a control group,
4:29there was no placebo control. So, maybe
4:31the cold showering groups chose to skip
4:33work less for some reason.
4:35It's not clear, but at least it didn't
4:37seem to show cold showering was harmful
4:39to immune function, at least in the
4:41short run in healthy [music] adults.
4:44In our next story, we look at which
4:46vegetables boost immune [music] function
4:49the most. What we eat or don't eat can
4:53affect [music] our immune system.
4:55This study was conducted to determine
4:57the effect of the consumption of
4:58brightly colored vegetables on the
5:00immune system.
5:01The first 2 weeks, basically no fruits
5:03and veggies. Then 2 weeks drinking a cup
5:05and a half of tomato juice every day.
5:07Then carrot juice. Then spinach powder.
5:11Within just 2 weeks of a fruit and
5:13veggie deficient diet, immune function
5:18plummets.
5:19But just a cup and a half of tomato
5:21juice and can bring us back from the
5:23ashes. Not five servings a day, just
5:26that one tall glass of tomato juice. But
5:29the carrot juice alone didn't seem to
5:31help as well. Nor did the powder
5:34equivalent of about one serving of
5:35spinach.
5:37This says to me two things. One, how
5:39remarkably we can affect our immune
5:41function with simple dietary decisions.
5:45And two, not all veggies are alike.
5:49Though this study was repeated looking
5:50at other immune markers and the tomato
5:53versus carrot appeared more evenly
5:55matched,
5:56there is one family of vegetables we
5:58definitely don't want to miss out on.
6:01Inflammation, leaky gut, all because of
6:04an absence of AHR ligands. In other
6:07words,
6:08an absence of cruciferous vegetables in
6:10our diet. Cabbage, collards,
6:12cauliflower, kale, brussels sprouts,
6:14broccoli.
6:16So, do people who eat healthier actually
6:19get sick less?
6:20Those who eat more fruits and vegetables
6:22appear to have a lower risk of getting
6:24an upper respiratory tract infection
6:25like the common cold, whether they're
6:27otherwise vegetarian or not. Even just
6:30one added apple a day
6:33may help keep the doctor away.
6:37Uh the common cold is so innocuous,
6:39though. Why not test against something
6:40stronger?
6:42One can also look at more serious
6:44respiratory infections like influenza.
6:46Looking at the relationship between
6:47various risk factors and
6:49influenza-related hospitalizations in
6:51the United States,
6:53they found that a 5% increase in the
6:55prevalence of obesity was bad,
6:57associated with 6% increased
6:59hospitalization rate, but physical
7:01inactivity was worse, 7%. But just that
7:04tiny bump in the rates of low fruit and
7:07vegetable consumption may increase
7:09flu-related hospitalization rates even
7:12more.
7:14And the common cold isn't always
7:16innocuous. A common cold during the
7:18first trimester of pregnancy is
7:20associated with a number of birth
7:22defects, including one of the worst, um
7:24anencephaly, a
7:26fatal malformation of the brain.
7:29More recent data suggests it's the
7:31fever, as anti-fever drugs appeared able
7:35to prevent the possible birth
7:36defect-causing effect of the common
7:38cold.
7:39But But better to not get sick in the
7:42first place. A thousand women in their
7:44diets were followed before and during
7:46pregnancy, and women who consumed more
7:48fruits and vegetables had a moderate
7:50reduction in risk of upper respiratory
7:52tract infection during pregnancy, and
7:54this benefit appears to be derived from
7:56both fruits and vegetables instead of
7:58either alone.
8:00Whole fruits and vegetables provide a
8:02natural balance of all sorts of things
8:04that may improve our immune function in
8:05a complementary, combined, or
8:07synergistic manner that could account
8:09for the protective effect observed from
8:11high consumption of both fruits and
8:13vegetables.
8:14Or maybe that's the only way they got
8:16enough. The women who appeared protected
8:18in the study were eating nearly nine
8:20servings of fruits and vegetables a day
8:22compared with only five servings of
8:24fruits or four of veggies.
8:27That may fulfill some arbitrary five or
8:29six a day minimum, but may be
8:31insufficient for effective immunity.
8:35For example, in that famous study I
8:37profiled previously,
8:39elderly individuals randomized into a
8:41five a day group did have an improved
8:44antibody response to their pneumonia
8:47vaccination compared to just two
8:49servings of fruits and veggies a day, an
8:5180% increase.
8:54But only 30%
8:56reached their target levels, 12 out of
9:0040.
9:02Six times better than the two a day
9:04group, but maybe eight, nine, or 10 a
9:06day would have worked even better.
9:11Did you know that exercising may make
9:13our immune system more than five times
9:15better at fighting infection?
9:17Exercise [music] can boost our immune
9:19system by so much that we can reduce the
9:22number of symptom days by 25 to 50%.
9:25Imagine if there was some drug that
9:27could do that. Would rake in billions,
9:30whereas exercise is free and tends to
9:32only have good side effects.
9:34It doesn't even take much of a workout
9:36to get results. Studies find that if you
9:38let kids run around for just 6 minutes,
9:42the levels of immune cells circulating
9:44their blood can increase by 50% as they
9:46pour from the bone marrow and redeploy
9:48throughout the body. Even moderate
9:50exercise can also boost IgA production,
9:54protective antibodies that coat all of
9:55our moist membranes.
9:58Compared to a sedentary control group,
10:00those who performed aerobic exercises
10:03for 30 minutes three times a week for 12
10:05weeks had a 50% increase in the levels
10:07of IgA in their saliva and reported
10:10significantly fewer flu-related
10:12symptoms.
10:14Salivary IgA levels are associated with
10:16lower overall mortality risk over time,
10:18particularly cancer mortality, perhaps
10:21as a proxy for immune function more
10:23generally, and you can boost those
10:25levels with exercise.
10:28Exercise may also boost the activity of
10:30natural killer cells, our immune
10:32soldiers that focus on eliminating both
10:34tumor cells and virus-infected cells.
10:38Here are five different types of cancer
10:40growing in a petri dish, mostly
10:42leukemias and lymphomas. Draw blood from
10:45people and drip on some of their natural
10:47killer cells into the dish and they
10:49start killing off the cancer cells.
10:52Okay, but that was blood taken from
10:54someone before exercise. Draw blood
10:57after 30 minutes of cycling and drop on
11:00the same number of natural killer cells
11:02and they each kill cancer about 60%
11:05better.
11:06This may be one of the reasons why
11:07exercise seems to help both prevent
11:10cancer and improve cancer survival.
11:14Might it improve vaccination responses?
11:17If aerobic exercise gets your immune
11:19cells to spill out from your bones,
11:21can't you just flouch on the couch all
11:23year and just jump up and take a brisk
11:25walk right before getting the jab?
11:28Studies to this effect performed on
11:29young adults had inconsistent results.
11:32For example, improving the antibody
11:33response to a flu vaccine in women but
11:35not men or to a meningitis vaccine in
11:38men but not women.
11:40Against half doses
11:44or weaker vaccines, acute exercise
11:47interventions appeared to work better
11:49suggesting perhaps a ceiling effect
11:52whereby their immune responses were
11:54normally so robust, exercise might not
11:57improve them further. But maybe it would
11:59work more consistently in older adults.
12:03Sadly, 45-minute moderate-intensity
12:05aerobic exercise right before flu or
12:07pneumonia vaccinations didn't seem to
12:09help in older adults.
12:11Even 2 [clears throat] months of
12:1345-minute moderate-intensity daily
12:15activity 6 weeks before and 2 weeks
12:17after vaccination appeared insufficient
12:19to make a difference. Eccentric
12:22resistance exercise, for example, slowly
12:25lowering heavy dumbbells after bicep
12:27curls or lateral raises to inflame the
12:31muscles right before the vaccine goes in
12:33also doesn't seem to be a viable
12:35strategy.
12:37What about exercise to reduce infection
12:39risk directly?
12:41In a study entitled moderate exercise
12:43protects mice from death due to
12:45influenza virus, mice exercised for
12:4820-30 minutes 4 hours after flu virus
12:50exposure and then each of the next 3
12:52days had nearly twice the survival rate,
12:5518% dying compared to 57% dead in the
12:58sedentary group.
13:00There's nothing so dramatic in the human
13:02literature, but based on a study that
13:05followed more than a thousand adults
13:06through flu season, those who exercised
13:08even just a few days a week were sick
13:10about 40% fewer days than sedentary
13:13individuals. Randomized controlled
13:15interventional trials back this up. For
13:18example, one study found that while
13:19elderly sedentary women randomized to a
13:22mild range of motion and flexibility
13:24calisthenics control group had a 50%
13:28chance of getting an upper respiratory
13:29illness during the fall season. Those
13:31randomized to begin a half hour a day
13:33walking program dropped their risk down
13:36to 20%. For conditioned athletes though,
13:39the risk was just 8%.
13:41Exercising could potentially make our
13:44immune systems more than five times
13:45better at fighting infection.
13:48In a year-long study, sedentary
13:50postmenopausal women randomized to 45
13:52minutes of moderate intensity exercise
13:54five days per week were experiencing
13:56three times fewer colds by the end of
13:58the study compared to the control group
14:00who instead randomized to weekly
14:01stretching sessions. Even though the
14:04exercise group only ended up exercising
14:05around four times a week.
14:07A similar study of younger overweight
14:09women found that 15 weeks of daily
14:12walking cut the number of days sick from
14:14upper respiratory tract infection
14:16symptoms in half. Though [clears throat]
14:18this was due to cutting the duration of
14:20each episode in half rather than cutting
14:22down on the frequency of illness.
14:25In terms of more serious infections,
14:27randomizing older men and women to one
14:29hour exercise classes twice a week for
14:31two years did not unfortunately cut down
14:33the risk of coming down with pneumonia.
14:36Although yoga training can improve lung
14:38function in the elderly, it has yet to
14:40be shown to help prevent pneumonia
14:42either.
14:43There was however a treatment trial of
14:45yoga breathing exercises for pulmonary
14:48tuberculosis performed in India.
14:50Compared to a mindfulness meditation
14:53breathing awareness control group, those
14:55randomized to a yoga group cleared their
14:57active infections faster. Even laughter
15:01yoga might help.
15:03The evolution of laugh is thought to
15:05have been as an antidote to stress, the
15:07release of nervous energy. Within 60
15:10minutes of people watching a comedy
15:12video complete with Gallagher's classic
15:14Sledge-O-Matic finale,
15:16levels of the stress hormone cortisol in
15:18their bloodstreams were cut by more than
15:20half.
15:22Since cortisol acts as an
15:23immunosuppressant, which is why
15:25cortisol-like steroids like prednisone
15:27are used for inflammatory autoimmune
15:29diseases, the drop in cortisol with
15:31laughter may explain why those laughing
15:33heartily at a humorous video had
15:35improvements in natural killer cell
15:36function compared to those randomized to
15:38a control group watching tourism videos.
15:41Replicating these results today might
15:43[music] be difficult given the choice of
15:46comedic stimulus, Bill Cosby.
15:50Visit nutritionfacts.org/audio
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16:05and How Not to Age is all at
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17:03Thanks for listening.