Is Too Much Sleep as Bad as Too Little (Economist)

Summary

A Well Informed / Science & Technology column testing the "eight hours" rule (traced to Robert Owen's 1817 "eight hours labour, eight hours recreation, eight hours rest" — a labour slogan, not a medical finding). The evidence points to a U-shaped relationship: both short and long sleep are associated with worse health, with an optimal band of roughly 6.5-7.8 hours. The new contribution is a Nature study that locates the band organ by organ using biological-ageing clocks. The piece closes with the researchers' own caution against obsessing over a number.

Key claims

The two 2015 syntheses

• Sleep Health (National Sleep Foundation panel): reviewed 575 studies from 2004-2014; recommended 7-9 hours for adults 18-64, narrowing to 7-8 hours for over-65s.
• Sleep (AASM/SRS consensus): analysed 311 studies; concluded ~7 hours is the best target and flagged uncertainty about harm from regularly sleeping >9 hours.

The 2026 Nature "sleep chart" study (Wen et al., Columbia University; published 13 May 2026)

• Method: "biological clocks" that estimate whether a tissue is in better or worse condition than chronological age predicts, applied organ by organ. Built 23 clocks across 17 organ systems from imaging, plasma proteomics and metabolomics.
• Population: ~500,000 adults, mostly UK Biobank, aged 37-84; sleep duration self-reported.
• Finding: U-shaped relationship between sleep duration and biological age gap across nine body systems (brain, lungs, liver, skin among them). Lowest age gaps at 6.5-7.8 h for women and 6.4-7.7 h for men.
• Sleep <6 h or >8 h was associated with higher risk of systemic disease (short sleep: depression, anxiety, obesity, hypertension, type 2 diabetes, heart disease; both ends: COPD, asthma, GI conditions) and all-cause mortality. Ageing clocks appear to partially mediate the long-sleep-to-depression pathway, while short sleep shows a more direct link.

Expert framing

• Michael Grandner (University of Arizona): duration is one measure; quality, regularity and continuity also matter. "Don't freak out about any particular number, unless it's a very unusual number."
• Junhao Wen (lead author, self-described light sleeper): listen to your body; sleep enough to wake refreshed.
• AASM 2025 survey: 76% of respondents had lost sleep because of worry about sleep — the Orthosomnia irony.

What is flagged as unproven

• Causality is unresolved. The article and the authors say so explicitly: are organs older because their owners sleep too little, or does a third factor (illness, pain, depression) drive both the ageing signal and the abnormal sleep? Long sleep in particular may be a marker of existing illness rather than a cause of harm. The study's Mendelian-randomisation analysis did not establish that disease causes the sleep change.
• Population results do not map onto individuals. The optimal band is a population minimum; individual need varies.
• Self-reported sleep duration is the exposure measure, not device- or PSG-measured sleep.
• The 2015 Sleep consensus's uncertainty about >9 h remains: long-sleep harm is the less well-established arm of the U.

Closing line

"Aim for six to eight hours a night, in other words, but don't toss and turn over the precise number."

Wikilinks

The Economist — Science & Technology / Well Informed. Sleep Duration and Mortality — concept page: the U-shaped curve, the 2015 syntheses and the 2026 organ-clock refinement. Orthosomnia — worry about sleep as a cause of lost sleep. Sleep Tracking — the devices sold to hit the optimal band. Should You Use a Sleep Tracker (Economist) — companion piece (2026-06-06) that cites the same Nature study.

Captured-by trigger

Source file: Economist 2026-07-04 Science---Techn - Is too much sleep as bad as too little.md. Study details (DOI, 23 clocks / 17 organ systems, disease associations) cross-checked against the UK Biobank publications listing and secondary coverage (Managed Healthcare Executive, Down To Earth); the Nature page itself is paywalled.