Huberman's claims about exercise, cortisol, and immune function are wrong
Huberman's claims about exercise, cortisol, and immune function are wrong
For a gym bro, you'd think he'd be better versed on the topic
(Note: this is part three of a multi-piece segment, for the sake of length)
I thought I was going to wrap this in 3 parts, but there is still so much to say! If you missed part 1, which covers the public health burden of flu and the issues with Huberman downplaying the severity of the flu and benefits of vaccination, make sure to read that. Part 2 discusses the objectively false statements he made about the immune response to infection. This section will cover the segment about exercise, cortisol, and ‘bolstering the immune system’, and the final chapter (early next week), will cover final chunk.
For someone who is a hardcore gym bro and talks about exercise a lot, you’d think he’d at least have the exercise stuff down. Unfortunately, this is a common pattern: just because someone works out or is fit doesn’t mean they are an expert on science-related topics. And when it comes to the science of exercise, immune function, and cortisol, Huberman needs some education.
Now, if you’ve ever seen or heard me say anything about the immune system, you know that I always talk about fundamentals that equip your immune system with the tools it needs:
A diverse diet, rich in produce, fiber, and lean proteins. But this doesn’t mean eating things outside those ‘criteria’ in moderation is harmful.
Good quality sleep.
Routine physical activity.
Hydration.
Minimizing stress.
Hygiene practices: food hygiene, personal hygiene, hand hygiene, sexual hygiene.
Limiting alcohol consumption.
Avoiding tobacco, smoking, and nicotine products.
Maintaining a consistent and healthy weight for you.
Staying up-to-date on all recommended vaccinations.
But the only REAL way to boost your immune system is through vaccination.
I discussed how vaccines work and his false statements about flu vaccine in part 1, so I won’t rehash that here, but you must understand that if someone purporting to be providing a ‘science-backed’ discussion on cold and flu prevention doesn’t enthusiastically encourage flu vaccination, they’re doing the opposite. The data are unequivocal regarding the benefits and safety of flu vaccination.
Huberman notes that ‘the goal’ is to prevent infection in the first place, which is true. Vaccination is one of the best way to prevent infections, so why he discourages it by saying flu vaccines are ineffective against strains that aren’t in the vaccine, completely ignoring polyclonal immune responses, is baffling.
Just because vaccination is not 100% effective does not mean it is INEFFECTIVE.
There’s a weird disconnect among people when you talk about vaccines, especially ones like the flu vaccine. A repeat refrain of:
“But it’s only 50% effective”
SO? Nothing, literally nothing, is 100% effective.
Risk reduction is the goal. Vaccines aren’t magical force fields. Neither are seat belts. Neither are airbags. Neither are stop signs, or crosswalks, or speed limits. Neither is handwashing, or cooking food to minimum temperatures, or refrigeration. So, let’s stop with that mentality. 50% effective is better than 0% effective, which is what you have without the flu vaccine. And you aren’t comparing that to some massive risk of vaccination: flu vaccines are phenomenally safe and are recommended for everyone 6 months and older. They have been studied and developed since the 1950s.
Beyond that, the 50% isn’t the full story. That 50% is the median of the effectiveness at preventing symptomatic illness (typical range is 40-60% depending on the year).
In addition to preventing symptomatic illness 50% of the time, vaccination also:
Protects against severe illness and death.
Reduces risk of hospitalization.
Prevents infection in many cases.
Reduces viral load so you are less likely to infect someone else.
Prevents severe complications due to the flu.
In part 2, I discussed several mechanisms that immune memory, generated through vaccination, protects you:
Neutralizing antibodies produced by plasma cells can immediately recognize incoming virus, bind them and prevent them from getting into our cells.
CD8 T cells can quickly detect cells that were infected early and directly kill them, halting progression of viral replication.
CD4 T cells augment these responses and help reduce viral load.
There is also a minimum dose for every pathogen that leads to successful infection. Exposure doesn’t guarantee infection, which is when the virus successfully colonizes your cells and starts replicating. You need to be exposed to a certain number of viral particles to develop infection. Vaccination can reduce viral load, which Huberman didn’t mention at all. Interestingly, he ALSO didn’t note other methods like mask wearing and improved ventilation that can reduce the number of viral particles you are exposed to, also reducing the risk of infection.
Infection requires exposure and duration. The longer you are near an infected person and the fewer defenses you have, the more likely you are to get infected.
An unvaccinated person with no mask in a larger room may be more likely to get infected than a vaccinated person wearing a mask in a smaller, less ventilated area, because their functional dose of virus when exposed to an infected person is higher.
Okay, so Huberman doesn’t discuss any of these evidence-based methods to prevent infection, but he does spend an inordinate amount of time on exercise. Yes, exercise is important - I am pretty sure that is unequivocally agreed upon, but like the rest of the content in the episode, he makes false statements and mischaracterizes all of the information related to the immune system.
Exercise does not “activate the immune system”.
Regular, moderate intensity exercise is beneficial for general health and supports immune system function through a variety of complex mechanisms. It is not uniquely “activating” specific cell types or pathways in the immune system, and the influence of exercise on immune system function is not solely through stress hormone pathways. In addition, the statement “exercise of specific type and specific duration and specific intensity can serve to bolster the innate immune system” is false. Huberman’s specific prescriptions for exercise (duration, type, intensity) are not supported by robust evidence. The benefits of exercise are highly dependent on the individual, and there is no evidence that “12 minutes of high intensity training” boosts immune function.
Marathon running does not cause “severe immune suppression”.
Hi, marathon runner and immunologist here. Huberman makes really reckless and alarmist statements claiming T cells, NK cells, and other components of the innate immune system have “huge reductions” after running a marathon or training for a marathon. Anything that puts your body under intense stress can temporarily dampen certain immune processes. This isn’t ‘severe immune compromise”, this is a regulatory process, and immune system function rebounds shortly thereafter (within 3 to 72 hours).
Also, how ableist is it that he says “maybe 4 hours to run a marathon if you’re really slow”? Anywho, a great segue into his completely false statements about stress and cortisol.
Huberman’s entire thesis on exercise, cortisol, and immune system activation is patently false.
Huberman talks a lot about the “post-exercise stress response” and how it tunes up your innate immune system, and increases cortisol which activates those NK cells. Guess what? That’s the EXACT OPPOSITE of what cortisol does to NK cells.
Cortisol does not activate natural killer cells of the innate immune system.
Cortisol is a steroid hormone produced by the adrenal glands in response to stress and low blood sugar. While the cellular processes it acts upon are complex, cortisol and glucocorticoids are generally immunosuppressive, meaning they dampen immune responses.
In fact, cortisol inhibits the activation of NK cells as well as T cells and impairs their function. This phenomenon was first described in the 1980s. Cortisol alters gene expression of NK cells which causes them to downregulate proteins that they need for function: including those chemicals I discussed in part 2, perforin and granzymes, which they secrete to kill virally-infected cells. Honestly, I’m baffled as to how someone could get this so wrong.
So cortisol is not augmenting NK cell function. In the context of viral infections, inhibiting the activation of NK cells via high cortisol levels can be detrimental, and certainly does not promote fighting off infection. Ironically, some viruses hijack the cortisol pathway in order to suppress the immune response to infection as a survival mechanism for the virus.
Cortisol doesn’t promote production of interleukin-1 and interleukin-6, either.
Huberman is weirdly fixated on cortisol, NK cells, and 2 specific cytokines, interleukins-1 and -6 (IL-1 and IL-6). I’m guessing he cherry-picked a really poorly done paper that made claims about IL-1, IL-6, NK cells, and cortisol. IL-1 and IL-6 are important pro-inflammatory cytokines that are produced by a variety of cell types, including macrophages, dendritic cells, epithelial and endothelial cells produce IL-1 and IL-6 (T cells and B cells also produce IL-6). These two cytokines are involved in immune response to infection, and help to activate cells of the adaptive immune system.
But cortisol inhibits the production of these pro-inflammatory cytokines. That is why glucocorticoids (corticosteroids) are used as therapeutic treatments for inflammatory diseases. Because they are immunosuppressive. It’s also why people on corticosteroid treatments are more susceptible to infection. Cortisol isn’t helping “prevent colds and flu”, contrary to what Huberman thinks.
Caffeine doesn’t give you energy.
In this whole circuitous and mischaracterized spiel about exercise, Huberman talks about how it’s fine to ingest your caffeine right away if you work out in the morning because it will give you an increase in energy. This is not how caffeine works. Caffeine does not provide energy. Energy is calories (technically, energy to our body is ATP, but it’s generated through the ingestion of calorie-containing substances). Caffeine is a stimulant and it increases alertness by binding adenosine receptors. By blocking adenosine receptors, it inhibits adenosine from binding which normally promotes relaxation and sleep. It can also indirectly increases the activity of other neurotransmitters like dopamine and norepinephrine, which can also augment alertness and focus, not energy.
(You’d think that these chemicals that are at least related to neuroscience would be in his wheelhouse.)
Exercise is healthy for you, to be sure. But a prescribed specific exercise regimen of specific duration isn’t offering a unique benefit. Exercise isn’t “activating” your immune system. Neither is cortisol. Exercise in and of itself is not going to prevent infection with respiratory viral illnesses. As I said, it is simply one of the fundamentals of a healthy lifestyle.
While some people may wave off these errors as insignificant in the grand scheme of things, the misrepresentation of physiologic phenomenon is a theme in Huberman’s content.
These false statements mislead the public and erode science literacy. More than that, he uses his authority to convince people he is credible, so that when he promotes more harmful misinformation, he has a captive audience that is vulnerable to predatory pseudoscience.
More on that in the next (and final) section.