Newsletter #192

Good morning, humanOS friends! So, the burgeoning post-holiday surge in Omicron has tilted my attention back to the immune system. Once you’ve gotten your vaccines and boosters, is there anything else you can do to make sure your body’s defenses are at their best?

Well, maybe. Of course, there are tons of articles hyping products to “boost” the immune system - many of which aren’t necessarily super credible. That having been said, there is reason to believe that aspects of lifestyle contribute to healthy immune function. For example, observational studies have shown that people with higher self-reported levels of physical activity are less likely to contract an upper respiratory tract infection, and army recruits who report sleeping less than six hours per night are four times more likely to be diagnosed with a URTI. However, this type of research is always accompanied by several limitations.

This is why live viral challenge trials are so useful. Sheldon Cohen at Carnegie Mellon has spent decades performing studies in which some brave volunteers are administered nasal drops containing either respiratory viruses or saline (placebo), and then keeping them in quarantine to see if they get sick. This experimental design is obviously more rigorous, and can more readily establish a causal relationship between infection and the factors of interest. He has conducted numerous studies in this format to examine the impact of exercise, psychological stress, and dimensions of sleep on susceptibility to infection. Let’s take a look at what he has found. 👀

Cohen and colleagues recruited 276 participants from the Pittsburgh area and assessed various aspects of their lifestyle, such as social networks and physical activity. The team then gave subjects nasal drops containing one of two rhinoviruses (the pathogen predominantly linked to common cold), and admitted them into quarantine for five days to monitor for subsequent infection. They found that participants who exercised less than twice per week were 1.8 times more likely to go on to develop a cold. Other factors associated with greater risk of illness were smoking and consuming less than 85mg per day of vitamin C. The relationship between exercise and immunity is a little complicated - you can check out this blog to learn more.

In this study, the same viral-challenge paradigm was used, but the researchers first assessed acute and chronic stressors via an intensive interview technique before exposing the volunteers to upper respiratory viruses. They found that acute stressors preceding quarantine were not associated with greater likelihood of going on to develop a cold. However, exposure to chronic stress dramatically increased their probability of getting sick, and the longer the duration of the stressor, the greater the risk. Why might this be? Well, the stress hormone cortisol is actually a fairly potent anti-inflammatory, so this is sort of paradoxical. However, it is now believed that prolonged elevations in cortisol due to chronic stress gradually makes tissues in the body less sensitive to its anti-inflammatory effects through a phenomenon known as glucocorticoid receptor resistance. (This is analogous to insulin resistance - your body is churning out the hormone, but your cells can no longer "hear" the message.) This, in turn, amplifies the risk for an exaggerated inflammatory response and more serious disease when someone gets sick.

The researchers recruited 153 healthy volunteers and had them report how much sleep they were getting, as well as their sleep efficiency (meaning the percentage of time spent in bed when they were actually asleep, as opposed to lying awake trying to fall asleep) for a period of 14 days. Then, like in the aforementioned studies, the participants were quarantined, administered nasal drops containing a rhinovirus, and monitored for the following week. As you might expect, less sleep was associated with greater risk of illness. The subjects who were getting less than 7 hours of sleep per night were 2.94 times more likely to go on to develop a cold, compared to those who averaged 8 hours. But the study also found that people with less than 92% sleep efficiency were 5 and a half times more likely to develop a cold, compared to those with sleep efficiency of 98% or more! So even if you’re in bed for more than eight hours, you may still be at substantially greater risk of getting sick if you are waking up a lot and having trouble getting back to sleep, or if you’re taking a long time to doze off. Incidentally, research also shows that people whose sleep is restricted generate fewer antibodies in response to vaccines, such as flu and hepatitis. So if you’re getting your booster soon, you should make sure to get plenty of sleep - both before and after the shot!

When you try to picture Holly, you think of those bright red berries, surrounded by leaves with sharp pointed edges, right?

However, if you look a little closer at a given tree, you’ll see that the leaves actually vary considerably in how spiky they are. The leaves up high will have smooth edges, while the leaves closer to the ground will be super prickly. There is good reason for this - the leaves growing close to the ground are within reach of deer, and the spikes have evolved to discourage these hungry herbivores.

That makes sense, right? But the crazy part is that this variation happens quickly, via epigenetic modifications, in direct response to animals munching on them. Researchers in Spain compared the DNA methylation patterns of prickly and non-prickly leaves from the same tree. They found that the DNA of prickly leaves was significantly less methylated than non-prickly leaves, and these alterations in methylation were in specific genetic markers (not just randomly distributed across the genome). Finally, browsing damage from deer was linked to the subsequent development of prickly leaves. Plants can’t run away from predators, but that doesn’t mean that they cannot adapt and fight back (in a sense).

As we progress into summertime and appear to be emerging from the worst of the pandemic (knock on wood), it seems like more and more people are getting out and traveling again. Consequently, a lot of us are probably going to be battling jet lag, perhaps for the first time in a while. Jet lag simply refers to a misalignment between the timing of your body clock and the timing of your environment. And until your body becomes re-synchronized to your new time zone, your physical and mental performance is apt to suffer. Is it possible to accelerate this adaptation?

Yes! That’s why we developed this guide, based on state-of-the-art research on circadian alignment. In this doc, we tell you how you can adjust to a new time zone faster, and even give you instructions on how to put together a simple DIY device to shift your body clock really fast (we call it Time Warp). You can also refer to our past interview with Stanford professor Jamie Zeitzer, an expert on jetlag who has done a ton of research on novel ways to adjust to transmeridian travel.

Thanks for reading, and we'll see y'all next week!

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