A cold plunge initially drives a strong fight-or-flight response. Stay in, and heart rate may start falling as parasympathetic activity increases. Kevin Tracey explains why the real physiology is more complicated than “stimulate your vagus nerve.”

HRV is not a direct measurement of “vagal tone.” Breathing, posture, sympathetic activity, irregular beats and even the calculation method can change it. Kevin Tracey explains what HRV can and can’t tell you. 📺 Watch on YouTube: youtu.be/x_h6Dd_Ap_o

Breathing and humming may involve vagus nerve activity. That doesn’t make them “vagus nerve stimulation.” Kevin Tracey on how wellness culture has stretched the term far beyond what the science supports. 📺 Watch on YouTube: youtu.be/x_h6Dd_Ap_o

Taxi and ambulance drivers had the lowest Alzheimer’s mortality among hundreds of occupations in Anupam Jena’s study. The possible link: constant use of spatial memory and the hippocampus. Fascinating hypothesis, not evidence that driving prevents Alzheimer’s.

You take an antibiotic, feel better two days later, and assume it worked. But what if you would’ve recovered anyway? Anupam Jena on the counterfactual problem that can make N-of-1 health experiments misleading. 📺 Watch on YouTube: youtu.be/k9XI7ym7iP8

“Meta-analysis” isn’t a magic word. If the underlying studies are weak, combining them doesn’t create strong evidence. Anupam Jena on why the label matters far less than what actually went into the analysis.

Even a high-quality study should usually change your mind only a little. It may not apply perfectly to you, and another good study may disagree. Anupam Jena on why health evidence should update your beliefs, not constantly overturn them.

As health measurement gets more predictive, we’ll increasingly discover things before we can treat them. Daniel Durand’s question: should medicine assume that knowledge itself is harmful, or should patients decide how much they want to know?

Daniel Durand cites research in 9,000+ people showing whole-body MRI detects cancer in ~1.6% of normal-risk participants. That’s part of the affirmative case. The unresolved question is whether detecting more disease translates into better long-term outcomes.

Whole-body MRI isn’t a replacement for every screening test. Blood cancers may need blood-based approaches, high-risk lung screening still calls for CT, and colonoscopy can actually remove precancerous polyps. Daniel Durand on where MRI falls short.