Newsletter #155: Antihistamines & Exercise 🤧💪🏽
Welcome, as always, to the humanOS newsletter! This week, we once again came across some cool research on exercise. Always a juicy topic, right?
We learned that better cardiorespiratory fitness improves cognitive performance in young adults through changes in the structure of the brain, that physical inactivity is one of the strongest risk factors for severe COVID-19, and that antihistamines appear to interfere with training adaptations and the health benefits associated with exercise.
So, um....does this mean that Claritin will kill your gains? 🤔
To find out more, scroll down 👇🏼
This Week’s Research Highlights
🤧 Antihistamines may reduce the benefits of exercise.
Recent research suggests that histamine may mediate various important physiological responses to exercise. This raises the question of whether suppressing histamine production with medication might have an impact on training adaptations.

To explore this question, researchers from Ghent University and the University of Copenhagen performed two experiments. In the first, they had eight participants ride an exercise bike for 40 minutes without antihistamines, then do the same exercise after taking two over-the-counter antihistamines. Typically after exercising, blood flow to muscles is dramatically boosted, but this effect was significantly dampened when participants took antihistamines. Next, the researchers had 18 men embark on a training program on the bikes, exercising three times per week for six weeks. Participants were randomly assigned to take either placebo or the aforementioned antihistamines. Those who had been taking antihistamines showed less improvement in exercise efficiency, blood flow, and muscle growth, compared to placebo. Insulin sensitivity and response to an oral glucose tolerance test significantly improved for controls, but did not at all in the antihistamine group. Why? One of the roles of histamine in the body is to regulate blood flow in muscles, and boosted blood flow is crucial for repairing and building muscles. Important note: The antihistamine dosing in this study was quite high (540 mg of fexofenadine/Allegra and 300 mg of ranitidine/Zantac or 40 mg of famotidine/Pepcid), and they used drugs to block both H1 and H2 receptors. So I wouldn’t panic about this, at least until a more normal dosing regimen is tested.
🏃♀️ Better cardiorespiratory fitness improves brain performance in young adults.
Researchers randomly assigned healthy young adults to participate in either a moderate aerobic exercise intervention program (exercise group; n= 48) or a group advised not to exercise at all (waitlist control group; n = 72). After nine weeks, the cardiorespiratory fitness of the exercise group significantly improved (as you’d expect). More interestingly, their performance on a test of executive function also got better after the exercise intervention. Brain imaging revealed some interesting changes in the structure of their brains, including increased gray matter volume in the left medial frontal gyrus, a part of the brain associated with executive functions. When the researchers analyzed the observed relationships, they found that the improvements in cardiorespiratory fitness were linked to the gray matter changes and enhancement of executive control.
🦠 Physical inactivity is associated with higher risk of severe COVID-19.
Researchers identified 48440 adult patients with a COVID-19 diagnosis from January to October of 2020, and linked their self-reported physical activity levels to their risk of adverse COVID-19 outcomes. The team determined that patients with COVID-19 who were consistently inactive were more than twice as likely to be admitted to the hospital, compared to those who reported meeting the national guidelines of 150+ minutes of physical activity every week. Inactive individuals were also 73% more likely to be admitted to ICU, and 2.49 times greater odds of dying from the infection, compared to those consistently meeting physical activity guidelines. The researchers conclude: "It is notable that being consistently inactive was a stronger risk factor for severe COVID-19 outcomes than any of the underlying medical conditions and risk factors identified by CDC except for age and a history of organ transplant. In fact, physical inactivity was the strongest risk factor across all outcomes, compared with the commonly cited modifiable risk factors, including smoking, obesity, diabetes, hypertension, cardiovascular disease and cancer.”
Question of the Week
🐎 More than a century ago, a horse named Clever Hans was said to be able to add, subtract, multiply, divide, work with fractions, and perform other mathematical feats that most would consider far beyond equine intellectual capacity. What was his secret?

💡 Answer
Podcasts We Loved This Week
- Alison Gopnik: Why adults lose the “beginner’s mind”: What children can teach adults about learning, consciousness, and play. Via the Ezra Klein Show.
- Brian Deer: A tale of scientific fraud—exposing Andrew Wakefield and the origin of the belief that vaccines cause autism. Via The Peter Attia Drive Podcast.
Products We Are Enjoying
Forest (Apple, Google Play)
Forest is a very simple productivity app, mixed with a little bit of farm simulation. Whenever you want to focus, you plant a tree, and as you are working with the app open, the tree grows. But if you leave the app, the tree withers and dies. Thus, over time, as you work, your forest grows lusher and more diverse. Very clever way to keep you from playing on the phone and remain focused.