Too little sleep and too much both age every organ system. The sweet spot is boring.

A paper in Nature today, described by Columbia University, takes the biological-age idea the consumer industry sells one number at a time and runs it properly: 23 aging clocks built from brain and body imaging, blood proteins and metabolites, spanning 17 organ systems, in UK Biobank participants aged 37 to 84. Against self-reported sleep, every system traced the same U. People sleeping roughly 6.4 to 7.8 hours had the smallest gap between their biological and calendar age; shorter and longer sleep were both associated with older-looking organs, and with higher rates of depression, diabetes, heart disease and death. The researchers ran a genetic analysis to test whether disease was driving the sleep rather than the reverse and found no strong evidence of it, while saying plainly that reverse causation cannot be fully excluded. Publicly funded; the authors declare no competing interests.

What is new, and what is the same. The range is not news — six to eight hours has been the consistent answer in every large cohort for a decade. What is new is the instrument: this is not a questionnaire about how people feel but a measurement of how old their heart, liver, brain and immune system look, and all of them agree. That agreement is worth more than any single clock, and it is the opposite of what a kit tells you. A kit reports one clock, built by one vendor, on one sample. This paper reports seventeen systems moving together, and the thing moving them is the amount of sleep, not a supplement.

Loree’s take

The patients I worry about are at both ends of the U and both think they are fine. The six-hour sleeper is proud of it; the nine-hour sleeper has a device that congratulates them. This study says the organs disagree with both. I do not prescribe a number of hours. I ask what time the alarm goes off and work backward to a bedtime that lands in the range, and I ask the long sleepers what is making them tired, because that is usually the finding.

Ben’s take

Note the shape of the finding: a U, with a floor you cannot buy your way below. There is no product for the bottom of a U. There are products for both arms — the one that promises to make six hours enough, and the one that tracks the nine — and neither of them moves you toward the middle. The middle is a bedtime. It is also, this paper says, every organ you own.

Why it matters to a recovering optimizer. If you are measuring your sleep, measure the one thing seventeen organ systems agreed on: the hours. Not the stages, not the score, not the readiness. The hours, in the range, most nights. That is the whole intervention, and it is the one the sleep industry cannot improve on because it has nothing to add to it.