Self & Other
13. The Things That Actually Help
Before the list, we need to be careful about what kind of list this is.
The wellness section of any bookstore is full of books that promise to tell you how to optimize, hack, supercharge, or otherwise upgrade your immune system. We have spent twelve chapters arguing that this framing is wrong on its own terms. What you want is not a stronger immune system but a well-regulated one. A boosted immune system is, by definition, more likely to over-respond — to inflame chronically, attack the wrong things, do the kinds of damage we spent the last several chapters describing. Nobody actually wants this. The wellness industry just hasn’t been told.
So this chapter is not a list of things that will boost your immune system. It is a list of things that, on the available evidence, support the immune system you already have. A few have remarkably strong evidence behind them. None are products you have to buy. Most are inconvenient in their own small ways, which is probably why nobody runs ad campaigns about them. They come down to taking reasonable care of an animal, which is what you are.
One more caveat. Nothing here is going to cure or prevent autoimmune disease, make a person with primary immunodeficiency stop getting infections, or eliminate the chance of cancer. These interventions are about averages and everyday well-being, not about overcoming serious medical conditions. If you have one of those, please do not read this chapter as a critique of why you are sick. The science we have already discussed is unambiguous: serious immune-related diseases are not the result of failing to do these things.
With those caveats, here are the things, in roughly the order of how strong the evidence is.
Sleep
The strongest evidence for any single lifestyle intervention on immune function, by a substantial margin, is for sleep.
People know sleep matters. Most popular wellness books touch on it. But the depth of how much it matters has only become clear in the last twenty years, and most of the public still does not understand the size of the effect.
A sample of the evidence. In a now-classic experiment by Aric Prather and colleagues, healthy adults were exposed to a rhinovirus — the kind of virus that causes the common cold — by having drops put directly into their noses. The researchers had measured the participants’ sleep over the previous week. The ones who had averaged less than six hours a night were more than four times as likely to develop a clinical cold as those who had averaged more than seven. Same exposure. Same virus. Same controlled conditions. The only relevant difference was sleep.
Even a single night of partial sleep loss reduces the response to vaccines by a meaningful margin. People who sleep poorly the night before a flu shot or a hepatitis vaccination produce fewer antibodies than people who sleep well, and the effect persists for weeks. People with chronic insomnia have measurable changes in T cell populations and inflammatory markers. People who routinely sleep fewer than six hours a night have higher rates of essentially every chronic disease that has been studied.
Why? The immune system, like the rest of the body, runs on a daily cycle. Cytokine production, T cell trafficking, and the formation of immunological memory all have circadian rhythms, and many of the most important consolidation processes appear to happen during deep sleep. Sleep is when the immune system does some of its most important paperwork. Disrupting it has the effect you’d expect from disrupting paperwork in any other office: things still get done, but worse, and important documents get lost.
The amount of sleep that supports normal immune function in most adults is seven to nine hours, with seven the lower end of where things start to be fine. Less than six is bad, and the badness compounds. Teenagers, including those reading this book, need closer to nine — and almost none of them get it. The reasons are partly biological (adolescent circadian rhythms genuinely shift later) and partly social (school start times, screens, social pressure). The result is a generation running their immune systems on insufficient sleep for years.
If you take only one thing away from this chapter, it should be that sleep is not optional. It is not a productivity drain you can hack around. It is one of the most important things your body does.
Movement
Regular, moderate exercise has well-documented effects on immune function. It also has a complicated dose-response curve.
Moderate exercise — brisk walking, easy cycling, light hiking, the kind of movement that raises the heart rate without ruining the rest of the day — supports normal immune function in several ways. It reduces baseline inflammation. It improves circulation of immune cells through tissues. It helps with sleep. It moderates stress. People who get about thirty minutes of moderate movement most days have lower rates of most chronic diseases and somewhat better responses to vaccines.
Vigorous exercise is more complicated. The standard finding, sometimes called the J-curve, is that very high training loads — the kind marathon runners and elite endurance athletes accumulate — are associated with somewhat increased rates of upper respiratory infections in the days following major efforts. Marathon runners get more colds in the week after a race than non-runners do in any given week. Olympic-level training has been shown to depress certain immune cell functions for hours to days afterward. The body is rebuilding from the effort, and during that rebuild, immune surveillance gets some of its budget cut.