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Population study: followed a group

Study that followed 322,721 Asian adults: lowest death risk at 7 hours of sleep

Svensson and colleagues · JAMA network open · 2021

Original title: Association of Sleep Duration With All- and Major-Cause Mortality Among Adults in Japan, China, Singapore, and Korea.

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What the study found

Mixed

Seven hours was the low point for death from all causes, heart disease and other causes. All-cause death was J-shaped, highest at 10 h or more for men (HR, 1.34; 95% CI, 1.26-1.44) and women (HR, 1.48; 95% CI, 1.36-1.61).

The study at a glance

Type of study
Population study: followed a group
Who or what was studied
322,721 people · adults in 9 Asian cohorts, average age 54.5, followed about 14 years
What was tested
Sleep hours compared with 7 hours, then deaths
What it measured
The question itself: death, heart disease and other health outcomes
Who has a stake
Company stake
One author reports personal fees from many drug companies and grants from several, stated as outside this work.
Journal
JAMA network open, 2021
Source
PubMed record 34477853. This page is based on the abstract only.

How much this study counts

  • –Shows a link, not a cause: people chose their own habits, and other differences between them may explain the result.
  • ✓Followed people over time, so habits were recorded before the outcome happened.
  • ✓Large: 322,721 people.
  • ✓Measured the question itself: death, heart disease and other health outcomes.
  • –Company stake: One author reports personal fees from many drug companies and grants from several, stated as outside this work.
  • •Summarized from the PubMed abstract only. The full paper may hold details the abstract leaves out.

✓ Strength– Limit• Note

These points come from fixed rules about the type of study, its size and length, what it measured, and who has a stake. Every study on Digestery gets the same rules.

Where this study sits

Each dot is one on-topic paper on this question. Steps near the top answer the question more directly.

↑ Stronger evidence

  1. Trials in people: death and chronic disease

    0

    Not done yet. This is the step that would answer the question.

  2. Trials in people: other measures

    1

    1 benefit

  3. Trials in people: lab tests or safety

    0

    None among the papers we read.

  4. Population studies

    11

    5 benefit, 4 mixed, 2 no difference

    ↑ This study is the ringed dot

  5. Blood levels and genes

    1

    1 benefit

↓ Weaker evidence

  • Points to benefit
  • Mixed
  • No difference
  • No direction
  • Points to harm

How it fits with the other research

The short answer to “How much sleep do adults need for good health?”

Lowest risk at about 7 hours.

Confidence: low. Based on 22 on-topic papers.

Read the full answer

Of the other 10 papers on the same step: 5 benefit, 3 mixed, 2 no difference. This one found mixed.

  • Quoted in “What we found”: Death risk was lowest at 7 hours in two cohorts: 322 721 adults in Japan, China, Singapore and Korea, and 25,430 adults in Sweden.
  • Part of the finding “Death risk is lowest near 7 hours”.
  • Open item for a person: Svensson 2021 coded company stake for one author's drug-company fees stated outside the work; confirm this should count.

Other papers on the same step

See all 22 studies on this question

How this page was made

Label

First read of the abstract
Claude Sonnet
Independent second read
Claude Haiku
Differences settled
The two reads agreed on every checked field. Claude Opus 5.5.
Headline
Claude Sonnet, from the checked study record. A script checked its numbers and wording.
Numbers
Checked against the abstract by a script
“How much this study counts”
Fixed rules, the same for every study
Source check by a person
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