Full Transcript Cold Exposure and Immune Function 0:01 We have lots of choices to make about our diet and to that doing the right 0:06 thing when it comes to treating a chronic disease or fighting a virus or 0:10 losing weight and suddenly our nutrition choices can seem almost 0:15 overwhelming. Well, I'm here to help. Welcome to the 0:19 NutritionFacts podcast. I'm your host Dr. Michael Greger. Today we look at the 0:23 different ways we can improve immune function and we start with one that 0:28 might surprise you. >> Several studies have demonstrated that 0:32 cold temperatures may be a potential risk factor for cancer development. For 0:36 example, this study compared the 50 countries with the highest cancer rates 0:40 to the countries with the lowest cancer rates and conclude that people living in 0:44 cold environments may have a higher risk of getting and dying from cancer. 0:50 A similar study within the United States found that colder counties were 0:53 associated with a greater cancer incidence. 0:56 But couldn't something like vitamin D exposure better explain these findings? 1:00 Patients diagnosed with cancer during summer months may have a better 1:03 prognosis than those diagnosed during the winter, but again this could be 1:07 because of the sunshine vitamin, vitamin D. Evidently an animal colony had less 1:12 cancer when they moved from a colder country to a warmer country based on 1:15 some observation published in 1939. That seems a bit of a stretch. But then this 1:22 study was published. Standard housing temperatures for 1:26 laboratory mice in research facilities is mandated to be between 20 and 26°C 1:32 unlike typical room temperatures in the 70s Fahrenheit. 1:36 But that's chilly for mice causing chronic mild cold stress. When that 1:41 stress is alleviated by housing at warmer temperatures like in the 80s 1:45 Fahrenheit, researchers observed a striking reduction in tumor formation, 1:50 cancer growth rate, and metastasis. Warmer was better. 1:54 They They that the cold stress results in a suppression of anti-tumor immunity. 2:00 Then why do they keep mice at that lower temperature? 2:04 It reduces the frequency of cage cleaning and helps ensure the thermal 2:09 comfort of the staff. The proposed mechanism is the activation 2:13 of the fight or flight response at least through the release of the stress 2:16 hormone norepinephrine, also known as noradrenaline. 2:20 Take a dip in a typical cold plunge and there can be a doubling of 2:23 norepinephrine levels in the blood within minutes. And we don't seem to 2:26 habituate, meaning we get that same bump in norepinephrine after each cold water 2:31 immersion, even after 3 months of regular plunges. 2:35 Might that be suppressing immune function? Or might it instead be 2:40 hormesis, that which doesn't kill us makes us stronger? 2:44 Cold water swimmers claim to suffer fewer and milder infections as a result 2:49 of the practice. Even if that's true, cold water swimmers 2:53 are swimming. Maybe it's the exercise, not the cold. How would we figure this 2:58 out? To control for any effect of swimming, 3:02 researchers compared cold water swimmers to indoor heated pool swimmers and 3:08 found no difference in upper respiratory tract susceptibility between swimmers in 3:12 cold water and heated pools. Therefore, cold water swimming appears to have no 3:16 protective effect. What about regularly taking cold 3:21 showers? Cold showers were first designed for the purpose of {quote} 3:25 treating the insane and then used as an instrument of torture in prisons before 3:31 it started killing too many people. Rather than being abandoned, however, 3:36 the shower was transformed by the use of warm water to actually clean people. No 3:40 idea. If you randomize people to short daily 3:43 cold showers versus hot showers for a few months, regular cold shower exposure 3:48 does appear to put the immune system on high alert. Does that actually translate 3:52 into less sickness? There's only been this one randomized trial on the effect
Vegetables, Fruits, and Infection Risk 3:56 of cold showering on health and work, a randomized controlled trial. 4:00 Participants were randomized to shower as normal, but end their showers with 0, 4:05 30, 60, or 90 seconds of cold water. And compared to the no cold group, the 4:11 different cold water groups collectively had a 29% reduction of self-reported 4:15 sick leave from work, but no fewer self-reported days of sickness. 4:20 Uh so, maybe the cold showering made them less sick even though they were 4:24 sick for the same duration. The [clears throat] problem, of course, 4:27 is that while there was a control group, there was no placebo control. So, maybe 4:31 the cold showering groups chose to skip work less for some reason. 4:35 It's not clear, but at least it didn't seem to show cold showering was harmful 4:39 to immune function, at least in the short run in healthy [music] adults. 4:44 In our next story, we look at which vegetables boost immune [music] function 4:49 the most. What we eat or don't eat can affect [music] our immune system. 4:55 This study was conducted to determine the effect of the consumption of 4:58 brightly colored vegetables on the immune system. 5:01 The first 2 weeks, basically no fruits and veggies. Then 2 weeks drinking a cup 5:05 and a half of tomato juice every day. Then carrot juice. Then spinach powder. 5:11 Within just 2 weeks of a fruit and veggie deficient diet, immune function 5:18 plummets. But just a cup and a half of tomato 5:21 juice and can bring us back from the ashes. Not five servings a day, just 5:26 that one tall glass of tomato juice. But the carrot juice alone didn't seem to 5:31 help as well. Nor did the powder equivalent of about one serving of 5:35 spinach. This says to me two things. One, how 5:39 remarkably we can affect our immune function with simple dietary decisions. 5:45 And two, not all veggies are alike. Though this study was repeated looking 5:50 at other immune markers and the tomato versus carrot appeared more evenly 5:55 matched, there is one family of vegetables we 5:58 definitely don't want to miss out on. Inflammation, leaky gut, all because of 6:04 an absence of AHR ligands. In other words, 6:08 an absence of cruciferous vegetables in our diet. Cabbage, collards, 6:12 cauliflower, kale, brussels sprouts, broccoli. 6:16 So, do people who eat healthier actually get sick less? 6:20 Those who eat more fruits and vegetables appear to have a lower risk of getting 6:24 an upper respiratory tract infection like the common cold, whether they're 6:27 otherwise vegetarian or not. Even just one added apple a day 6:33 may help keep the doctor away. Uh the common cold is so innocuous, 6:39 though. Why not test against something stronger? 6:42 One can also look at more serious respiratory infections like influenza. 6:46 Looking at the relationship between various risk factors and 6:49 influenza-related hospitalizations in the United States, 6:53 they found that a 5% increase in the prevalence of obesity was bad, 6:57 associated with 6% increased hospitalization rate, but physical 7:01 inactivity was worse, 7%. But just that tiny bump in the rates of low fruit and 7:07 vegetable consumption may increase flu-related hospitalization rates even 7:12 more. And the common cold isn't always 7:16 innocuous. A common cold during the first trimester of pregnancy is 7:20 associated with a number of birth defects, including one of the worst, um 7:24 anencephaly, a fatal malformation of the brain. 7:29 More recent data suggests it's the fever, as anti-fever drugs appeared able 7:35 to prevent the possible birth defect-causing effect of the common 7:38 cold. But But better to not get sick in the 7:42 first place. A thousand women in their diets were followed before and during 7:46 pregnancy, and women who consumed more fruits and vegetables had a moderate 7:50 reduction in risk of upper respiratory tract infection during pregnancy, and 7:54 this benefit appears to be derived from both fruits and vegetables instead of 7:58 either alone. Whole fruits and vegetables provide a 8:02 natural balance of all sorts of things that may improve our immune function in 8:05 a complementary, combined, or synergistic manner that could account 8:09 for the protective effect observed from high consumption of both fruits and 8:13 vegetables. Or maybe that's the only way they got 8:16 enough. The women who appeared protected in the study were eating nearly nine 8:20 servings of fruits and vegetables a day compared with only five servings of 8:24 fruits or four of veggies. That may fulfill some arbitrary five or 8:29 six a day minimum, but may be insufficient for effective immunity. 8:35 For example, in that famous study I profiled previously, 8:39 elderly individuals randomized into a five a day group did have an improved 8:44 antibody response to their pneumonia vaccination compared to just two 8:49 servings of fruits and veggies a day, an 80% increase.
Exercise, Vaccines, and Infection Prevention 8:54 But only 30% reached their target levels, 12 out of 9:00 40. Six times better than the two a day 9:04 group, but maybe eight, nine, or 10 a day would have worked even better. 9:11 Did you know that exercising may make our immune system more than five times 9:15 better at fighting infection? Exercise [music] can boost our immune 9:19 system by so much that we can reduce the number of symptom days by 25 to 50%. 9:25 Imagine if there was some drug that could do that. Would rake in billions, 9:30 whereas exercise is free and tends to only have good side effects. 9:34 It doesn't even take much of a workout to get results. Studies find that if you 9:38 let kids run around for just 6 minutes, the levels of immune cells circulating 9:44 their blood can increase by 50% as they pour from the bone marrow and redeploy 9:48 throughout the body. Even moderate exercise can also boost IgA production, 9:54 protective antibodies that coat all of our moist membranes. 9:58 Compared to a sedentary control group, those who performed aerobic exercises 10:03 for 30 minutes three times a week for 12 weeks had a 50% increase in the levels 10:07 of IgA in their saliva and reported significantly fewer flu-related 10:12 symptoms. Salivary IgA levels are associated with 10:16 lower overall mortality risk over time, particularly cancer mortality, perhaps 10:21 as a proxy for immune function more generally, and you can boost those 10:25 levels with exercise. Exercise may also boost the activity of 10:30 natural killer cells, our immune soldiers that focus on eliminating both 10:34 tumor cells and virus-infected cells. Here are five different types of cancer 10:40 growing in a petri dish, mostly leukemias and lymphomas. Draw blood from 10:45 people and drip on some of their natural killer cells into the dish and they 10:49 start killing off the cancer cells. Okay, but that was blood taken from 10:54 someone before exercise. Draw blood after 30 minutes of cycling and drop on 11:00 the same number of natural killer cells and they each kill cancer about 60% 11:05 better. This may be one of the reasons why 11:07 exercise seems to help both prevent cancer and improve cancer survival. 11:14 Might it improve vaccination responses? If aerobic exercise gets your immune 11:19 cells to spill out from your bones, can't you just flouch on the couch all 11:23 year and just jump up and take a brisk walk right before getting the jab? 11:28 Studies to this effect performed on young adults had inconsistent results. 11:32 For example, improving the antibody response to a flu vaccine in women but 11:35 not men or to a meningitis vaccine in men but not women. 11:40 Against half doses or weaker vaccines, acute exercise 11:47 interventions appeared to work better suggesting perhaps a ceiling effect 11:52 whereby their immune responses were normally so robust, exercise might not 11:57 improve them further. But maybe it would work more consistently in older adults. 12:03 Sadly, 45-minute moderate-intensity aerobic exercise right before flu or 12:07 pneumonia vaccinations didn't seem to help in older adults. 12:11 Even 2 [clears throat] months of 45-minute moderate-intensity daily 12:15 activity 6 weeks before and 2 weeks after vaccination appeared insufficient 12:19 to make a difference. Eccentric resistance exercise, for example, slowly 12:25 lowering heavy dumbbells after bicep curls or lateral raises to inflame the 12:31 muscles right before the vaccine goes in also doesn't seem to be a viable 12:35 strategy. What about exercise to reduce infection 12:39 risk directly? In a study entitled moderate exercise 12:43 protects mice from death due to influenza virus, mice exercised for 12:48 20-30 minutes 4 hours after flu virus exposure and then each of the next 3 12:52 days had nearly twice the survival rate, 18% dying compared to 57% dead in the 12:58 sedentary group. There's nothing so dramatic in the human 13:02 literature, but based on a study that followed more than a thousand adults 13:06 through flu season, those who exercised even just a few days a week were sick 13:10 about 40% fewer days than sedentary individuals. Randomized controlled 13:15 interventional trials back this up. For example, one study found that while 13:19 elderly sedentary women randomized to a mild range of motion and flexibility 13:24 calisthenics control group had a 50% chance of getting an upper respiratory 13:29 illness during the fall season. Those randomized to begin a half hour a day 13:33 walking program dropped their risk down to 20%. For conditioned athletes though, 13:39 the risk was just 8%. Exercising could potentially make our 13:44 immune systems more than five times better at fighting infection. 13:48 In a year-long study, sedentary postmenopausal women randomized to 45 13:52 minutes of moderate intensity exercise five days per week were experiencing 13:56 three times fewer colds by the end of the study compared to the control group 14:00 who instead randomized to weekly stretching sessions. Even though the 14:04 exercise group only ended up exercising around four times a week. 14:07 A similar study of younger overweight women found that 15 weeks of daily 14:12 walking cut the number of days sick from upper respiratory tract infection 14:16 symptoms in half. Though [clears throat] this was due to cutting the duration of 14:20 each episode in half rather than cutting down on the frequency of illness. 14:25 In terms of more serious infections, randomizing older men and women to one 14:29 hour exercise classes twice a week for two years did not unfortunately cut down 14:33 the risk of coming down with pneumonia. Although yoga training can improve lung 14:38 function in the elderly, it has yet to be shown to help prevent pneumonia 14:42 either. There was however a treatment trial of 14:45 yoga breathing exercises for pulmonary tuberculosis performed in India. 14:50 Compared to a mindfulness meditation breathing awareness control group, those 14:55 randomized to a yoga group cleared their active infections faster. Even laughter 15:01 yoga might help. The evolution of laugh is thought to 15:05 have been as an antidote to stress, the release of nervous energy. Within 60 15:10 minutes of people watching a comedy video complete with Gallagher's classic 15:14 Sledge-O-Matic finale, levels of the stress hormone cortisol in 15:18 their bloodstreams were cut by more than half. 15:22 Since cortisol acts as an immunosuppressant, which is why 15:25 cortisol-like steroids like prednisone are used for inflammatory autoimmune 15:29 diseases, the drop in cortisol with laughter may explain why those laughing 15:33 heartily at a humorous video had improvements in natural killer cell 15:36 function compared to those randomized to a control group watching tourism videos. 15:41 Replicating these results today might [music] be difficult given the choice of 15:46 comedic stimulus, Bill Cosby. Visit nutritionfacts.org/audio 15:52 to see all the podcast episodes with descriptions that include links to 15:56 [music] their associated videos. Sources cited and other details are available on 16:00 each video's page. Information about my books, How Not to Die, How Not to Diet, 16:05 and How Not to Age is all at nutritionfacts.org/books, [music] 16:08 including 16:12 some of the newer titles, including Lowering LDL Cholesterol Naturally 16:15 [music] with Food. All proceeds from all book sales 16:21 uh that I get go to charity. And I've got a new book in the publication 16:26 pipeline, How Not to Hurt. It's going to be available on December 15th of this 16:31 year, 2026. And don't forget to sign up for our free 16:36 newsletter, nutritionfacts.org/subscribe, 16:39 to stay updated on the latest bite-size [music] 16:42 videos and articles. Nutritionfacts.org is a science-based nonprofit, and 16:46 everything on the website is free. There are no ads, no corporate sponsorship, no 16:51 kickbacks, strictly non-commercial, not selling anything. 16:54 Just put it up as a public service, as a labor of love, as a tribute to my 16:58 grandmother, whose own life was saved [music] with evidence-based nutrition. 17:03 Thanks for listening.
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