Keith Rabois

True. I haven’t looked at the papers Alexey worked from, but the first thing that comes to my mind with this kind of data is causation vs correlation. It’s similar to the weight vs mortality risk models: Sick people tend to be underweight, and sleeping a lot, etc.

it is causal.

the evidence of sleep on perfromance and productivity is unequivocal.

I just checked the book (The Telomere Effect). The study that's perhaps referred to here(Which Walker also mentions, the one about the civil servants) is an association study, not causal.

The one claim for "missing a night of sleep /sleeping badly" says it increased the levels of cortisol.

is short-term increase in cortisol unhealthy? or is it just a temporary stress reaction like an increased heart rate during exercise?

I haven't even checked the paper itself, that's a separate question. But causally, it strikes me as odd that just a night of sleep would cause anything to telomeres. As far as I could find online ("rct telomere sleep") that has not been tested.