Boosting Immunity through Diet and Lifestyle

**Michael Greger** (0:00)
We have lots of choices to make about our diet. Add to that doing the right thing when it comes to treating a chronic disease, fighting a virus, or losing weight. And suddenly, our nutrition choices can seem almost overwhelming. Well, I'm here to help. Welcome to the Nutrition Facts Podcast. I'm your host, Dr. Michael Greger. Today we look at the different ways we can improve immune function, and we start with one that might surprise you. Several studies have demonstrated that cold temperatures may be a potential risk factor for cancer development. For example, this study compared the 50 countries with the highest cancer rates to the countries with the lowest cancer rates, and concluded that people living in cold environments may have a higher risk of getting and dying from cancer. A similar study within the United States found that colder counties were associated with a greater cancer incidence, but couldn't something like vitamin D exposure better explain these findings? Patients diagnosed with cancer during summer months may have a better prognosis than those diagnosed during the winter, but again this could be because of the sunshine vitamin, vitamin D. Evidently, an animal colony had less cancer when they moved from a colder country to a warmer country based on some observation published in 1939 That seems a bit of a stretch, but then this study was published. Standard housing temperatures for laboratory mice and research facilities is mandated to be between 20 and 26 Celsius, like typical room temperatures in the 70s Fahrenheit. But that's chilly for mice causing chronic mild cold stress. When that stress is alleviated by housing at warmer temperatures like in the 80s Fahrenheit, researchers observed a striking reduction in tumor formation, cancer growth rate, and metastasis. And warmer was better. They suggested that the cold stress results in a suppression of anti-tumor immunity.
Then why do they keep mice at that lower temperature? It reduces the frequency of cage cleaning and helps ensure the thermal comfort of the staff. The proposed mechanism is the activation of the fight-or-flight response that leads to the release of the stress hormone norepinephrine, also known as noradrenaline. Take a dip in a typical cold plunge and there can be a doubling of norepinephrine levels in the blood within minutes. And we don't seem to habituate, meaning we get that same bump in norepinephrine after each cold water immersion, even after three months of regular plunges. Might that be suppressing immune function? Or might it instead be hormesis, which doesn't kill us makes us stronger? Cold water swimmers claim to suffer fewer and milder infections as a result of the practice. Even if that's true, cold water swimmers are swimming. Maybe it's the exercise, not the cold. How would we figure this out? To control for any effect of swimming, researchers compared cold water swimmers to indoor heated pool swimmers, and found no difference in upper respiratory tract susceptibility between swimmers in cold water and heated pools. Therefore, cold water swimming appears to have no protective effect. What about regularly taking cold showers? Cold showers were first designed for the purpose of quote-unquote treating the insane, and then used as an instrument of torture in prisons before it started killing too many people. Rather than being abandoned, however, the shower was transformed by the use of warm water to actually clean people. I had no idea. If you randomize people to short daily cold showers versus hot showers for a few months, regular cold shower exposure does appear to put the immune system on high alert. Does that actually translate into less sickness? There's only been this one randomized trial on the effect of cold showering on health and work, a randomized controlled trial. Participants were randomized to shower as normal, but end their showers with 0, 30, 60, or 90 seconds of cold water. And compared to the no cold group, the different cold water groups collectively had a 29% reduction of self-reported sick leave from work, but no fewer self-reported days of sickness. So maybe the cold showering made them less sick, even though they were sick for the same duration. The problem, of course, is that while there was a control group, there was no placebo control, so maybe the cold showering groups chose to skip work less for some reason. It's not clear, but at least it didn't seem to show that cold showering was harmful to immune function, at least in the short run in healthy adults.
In our next story, we look at which vegetables boost immune function the most. What we eat or don't eat can affect our immune system. This study was conducted to determine the effect of the consumption of brightly colored vegetables on the immune system. The first two weeks, basically no fruits and veggies. Then, two weeks drinking a cup and a half of tomato juice every day, then carrot juice, then spinach powder. Within just two weeks of a fruit and veggie deficient diet, immune function plummets. But just a cup and a half of tomato juice can bring us back from the ashes. Not five servings a day, just that one tall glass of tomato juice. But the carrot juice alone didn't seem to help as well, nor did the powder equivalent of about one serving of spinach. This says to me two things. One, how remarkably we can affect our immune function with simple dietary decisions. And two, not all veggies are alike. Though this study was repeated looking at other immune markers, and the tomato versus carrot appeared more evenly matched, there is one family of vegetables we definitely don't want to miss out on.