Daily rhythm and metabolic syndrome: a study of 272 adults
Study of 272 adults with a wrist device: metabolic syndrome was linked more to heart rate rhythms than to sleep. An association, not a cause.
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What the studies say
Published studies on sleep, movement and eating, summarized. They help you understand. They are not medical advice for you.
Reading a summary
Each summary covers a study or article by others. It is not medical advice for you and does not replace your doctor. The source is at the bottom, with a link. Check what kind it is: a scientific journal and an article for the general public are not the same thing.
A study describes a group. Not you.
Sleep
Duration, regularity, stages: these studies look at the heart, the brain and metabolism. Each one is about a group of people.
Early Parkinson’s and REM disorder: a study of 413 people
Study of 413 people with early Parkinson's: probable REM sleep behaviour disorder was linked to faster cognitive decline. An association, not a cause.
Irregular sleep and the heart: a study of 1,992 adults
Study of 1,992 adults: highly variable sleep duration and timing were linked to about double the cardiovascular risk. An association, not a cause.
Sleep and atrial fibrillation: a study of 52,952 people
Study of 52,952 people with wearable devices: less deep and REM sleep was linked to more atrial fibrillation. An association, not a cause.
Sleep and cognitive decline: a review of 17 studies
Review of 17 longitudinal studies: fragmentation, less REM sleep and apnoea are linked to cognitive decline. The evidence is still mixed.
Sleep and dementia: an algorithm trained on nine measures
Study of an algorithm trained on age and nine sleep measures recorded at home: it matched the diagnosis in over 75% of cases. It still needs validation.
Sleep and disease risk: Stanford’s SleepFM model
Model trained on 585,000 hours of polysomnography: from one recorded night it estimates the risk of 130 conditions. A group finding.
Sleep and neurodegeneration: over a million health records
Analysis of over a million records, from a news report: sleep disorders were linked to higher risk of Alzheimer's and Parkinson's, up to 15 years earlier.
Sleep health in several dimensions: a 2025 AHA statement
2025 American Heart Association statement: sleep health has several dimensions, but for now Life's Essential 8 counts only its duration.
Sleep profiles, dementia and the heart: a study of 2,667 men
Study of 2,667 older men followed for 12 years: fragmented sleep was linked to more dementia and cardiovascular events. An association, not a cause.
Sleep stages and chronic disease: a study of 6,785 people
Study of 6,785 people with wearable devices: sleep stages were linked to several chronic diseases. An association, not a cause.
Before surgery, you plan your exercise with your doctor.
Steps and oxygenation
Steps, training and tissue oxygen, before and after surgery. Each study concerns a specific group: what applies to you is for your care team to decide.
ERAS and early mobilisation: a 2022 review
2022 review of early mobilisation in ERAS pathways: complications, walking again, hospital stay. A summary, not a new study.
Exercise and lung surgery: a meta-analysis of seven studies
Meta-analysis of seven studies, 404 people having lung cancer surgery: those who exercised first had fewer complications. The 5,000 steps come from one.
Exercise before major surgery: a 2014 review
2014 review: high-quality evidence for exercise before cardiovascular surgery; for other surgery, only circumstantial.
Exercise intensity and VO₂max: a meta-analysis of 14 trials
Meta-analysis of 14 randomised trials in abdominal and cardiothoracic surgery: effect of exercise on VO₂max 0.44, of HIIT 0.51. An average figure.
Microcirculation and wound healing: a handbook chapter
Handbook chapter: microcirculation carries oxygen and immune mediators to the surgical wound and supports its healing. A summary, not a new study.
Oxygen and wound healing: a 2004 review
2004 review: why the oxygen reaching the tissues matters for wound healing and resistance to infection. A summary, not a new study.
Oxygen and wound infection: a study of 500 patients
Randomised trial of 500 colorectal surgery patients: wound infections were 5.2% with 80% oxygen during surgery, 11.2% with 30%. A group finding.
Prehabilitation and complications: an educational article
2025 educational article: what prehabilitation is, with exercise and protein before surgery. Its figures do not name the study they come from.
Tissue oxygen and complications: a study of 124 patients
Study of 124 patients having major surgery: a lower minimum StO₂ during surgery was linked to more serious complications. An association, not a cause.
Training and lung complications: a 29-trial meta-analysis
Meta-analysis of 29 randomised trials: training before major surgery is linked to fewer lung complications (relative risk 0.52). An average figure.
Diet and sleep meet. Many studies look at both.
Diet and body composition
Body composition beyond weight, and the link between sleep and eating. What you eat is for you and your care team to decide.
A night without sleep and ghrelin: a study of nine men
Lab study of nine healthy men: after one night without sleep, ghrelin 22% higher and more hunger; leptin unchanged. A group finding.
A ring and personalised messages: a study of 56 adults
Study of 56 adults over a year, from UCLA Health: with a ring and personalised messages, sleep and activity improved more than in controls. A small group.
App, smart scale and weight loss: an analysis of 665 users
Retrospective analysis of 665 users with obesity of a fasting app: those who used it more lost more weight. An association, not a cause.
BMI and body composition: an educational article
Educational article: BMI relates weight to height, but it cannot tell fat from muscle or see visceral fat. It is not a study.
Body fat and metabolic risk: a trial protocol
Protocol of a randomised trial in 114 students: for the authors, body fat percentage says more about risk than BMI. It has no results yet.
Restricted sleep and hunger hormones: a study of 12 men
Crossover study of 12 healthy young men: after two days of restricted sleep, ghrelin +28%, leptin −18%, hunger +24%. A group finding.
Restricted sleep and snacks: a study of 19 men
Crossover study of 19 healthy young men: after four nights of restricted sleep, 328 more kcal from snacks, mostly carbohydrates. A group finding.
Short sleep and ghrelin: a meta-analysis of 21 studies
Meta-analysis of 21 studies with 2,250 people: ghrelin was higher with short sleep, with a small effect. An association, not a cause.
Sleep and weight loss: a study of 156 adults
Study of 156 adults with overweight followed for 18 months: those with more fragmented sleep lost less weight. An association, not a cause.
Sleep, activity, diet and wellbeing: three studies
Three studies of 2,086 young adults: sleep quality was the factor most linked to wellbeing, then fruit and vegetables. An association, not a cause.
Smartwatch, scale and visceral fat: a study of 60 adults
Study of 60 adults aged 40 and over, six months with a smartwatch and scale: those who also had monthly check-ups reduced visceral fat. A small group.
From the group to you
Studies are about groups. The Digital Twin, in trial on iPhone and on Android, lines up your data. It does not diagnose.