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Evidence & sources

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Health information is full of confident claims. Every lesson and technique here says how strong the evidence is, what is still uncertain, and where the ideas come from.

How the evidence levels work

These describe the research behind an idea — never you.

Strong evidence: Many good-quality studies, usually including randomised trials and reviews that pool them, point the same way. Guidelines tend to recommend it.
Moderate evidence: Several studies support it, but the effects are smaller, the studies are fewer or less rigorous, or results vary between groups.
Emerging evidence: Early or mixed research looks promising, but it is too soon to be confident. Treat it as worth trying, not proven.
Practical technique: A widely used, low-risk practice drawn from established approaches, but not tested much on its own. Its value is mostly that it is simple and harmless to try.
Evidence unclear: Researchers genuinely disagree, or findings have not held up when repeated. The lesson explains the different views.

Checking a health claim yourself

Six questions that work on a headline, a post or a product.

Is it one study, or many?: A single study — especially a small one — is a starting point. Confidence comes when many studies, ideally including reviews that pool them, point the same way.
Did they test it, or just notice it?: A trial that changes one thing and compares groups can show cause and effect. A study that only observes (people who sleep more are happier) shows a link, which could run either way or have a third cause.
How big was the effect?: “Significantly better” can mean a tiny difference. Ask how much it changed, not only whether it did.
Who was it tested on?: Results from university students, one country or people with a particular condition may not apply to you.
Who is saying it, and what are they selling?: Be more careful when the person making the claim profits from you believing it.
Does it promise a lot, fast, for everyone?: Real health changes are usually modest, gradual and different from person to person. Big, fast, universal promises are a warning sign.

Where the lessons come from

Organisations, guidelines and lines of research. Named, never quoted — the lessons put ideas in their own words.

Organisations

World Health Organization (WHO) — The UN’s health agency. Publishes guidance on mental health, self-care, physical activity, healthy diet and alcohol.
US National Institute of Mental Health (NIMH) — A US government research institute. Publishes plain-language information on caring for your mental health, stress, anxiety and depression, and on when to seek help.
American Psychological Association (APA) — The main professional body for psychologists in the US. Publishes public information on stress, resilience and psychological research.
American Academy of Sleep Medicine (AASM) — A professional society for sleep medicine. Its consensus recommends that adults regularly sleep seven hours or more a night.
US Centers for Disease Control and Prevention (CDC) — US public-health agency. Publishes practical guidance on sleep, physical activity and hygiene such as handwashing.

Guidelines and guidance

WHO guidance on self-care interventions — WHO’s framing of self-care as something people do to maintain their health, alongside — not instead of — professional care.
WHO “Doing What Matters in Times of Stress” — An illustrated self-help guide from WHO teaching practical stress-management skills such as grounding, unhooking from difficult thoughts and acting on values.
WHO guidelines on physical activity and sedentary behaviour (2020) — Recommends adults do 150–300 minutes of moderate aerobic activity a week (or 75–150 vigorous), plus muscle-strengthening on at least two days, and that every bit of movement counts.
WHO healthy diet guidance — Plain guidance on eating a variety of foods, plenty of fruit, vegetables and whole grains, and limiting free sugars, salt and some fats.
WHO statements on alcohol and health — WHO’s position that alcohol is harmful to health and that no level of drinking can be called safe for health.
WHO International Classification of Diseases (ICD-11) on burnout — Describes burnout as an occupational phenomenon resulting from chronic workplace stress — not as a medical condition.
UK National Institute for Health and Care Excellence (NICE) — Sets evidence-based treatment guidance in the UK, including for depression and anxiety, where guided self-help, behavioural activation and CBT appear among recommended options.
US Surgeon General advisories (2023) — Two public advisories: one on loneliness and social connection as a public-health issue, and one on social media and young people’s mental health, which called for more research and caution.

Lines of research

Cognitive behavioural therapy (CBT) research — Decades of research, beginning with Aaron Beck’s work, on how thoughts, feelings and behaviour interact, and on structured ways to test unhelpful thoughts.
Behavioural activation research — Studies, including trials and reviews, showing that planned increases in meaningful and enjoyable activity can reduce depressive symptoms.
Mindfulness-based programmes (MBSR, MBCT) — Research on structured mindfulness courses — Jon Kabat-Zinn’s stress-reduction programme and mindfulness-based cognitive therapy for preventing depression relapse.
Acceptance and commitment therapy (ACT) research — Research led by Steven Hayes and colleagues on psychological flexibility: making room for difficult experiences while acting on your values.
Self-compassion research — Kristin Neff’s and others’ research on treating yourself with the kindness you would offer a friend, and its links with wellbeing and motivation.
Emotion regulation research — James Gross’s process model of how people shape their emotions, and lab studies on putting feelings into words (affect labelling).
Stress physiology research — Research on the body’s stress systems — the fight-or-flight response and the longer cortisol response — and on the wear of long-term stress (allostatic load).
Slow-breathing and breathwork research — Reviews and trials on slow, paced breathing and its short-term effects on stress, heart rate and self-reported calm. Effects are real but modest, and studies vary.
Worry and anxiety research — Research on worry as avoidance, on postponing worry to a set time (stimulus control), and on intolerance of uncertainty as a driver of worry.
Problem-solving therapy research — Research on teaching structured problem solving, and WHO’s Problem Management Plus programme, which uses it as a core skill.
Attention and task-switching research — Lab research showing measurable costs when switching between tasks, and studies on how notifications and interruptions affect attention.
Research on digital media and wellbeing — A large, contested body of research on social media, screens and mental health. Associations are often small and causality is debated; some researchers argue the harms are larger than others accept.
Habit formation research — Research, including Wendy Wood’s and a well-known study by Phillippa Lally and colleagues, on how repetition in a stable context makes behaviour automatic — often over weeks to months.
Implementation intentions research — Peter Gollwitzer and Paschal Sheeran’s research showing that “if–then” plans help people follow through on intentions.
Procrastination research — Research by Piers Steel, Fuschia Sirois, Tim Pychyl and others showing procrastination is closely tied to avoiding unpleasant feelings, and that self-forgiveness helps people start again.
Motivation research (self-determination theory) — Edward Deci and Richard Ryan’s research on autonomy, competence and relatedness as the conditions that sustain motivation.
Social connection and health research — Research including large reviews by Julianne Holt-Lunstad linking social connection with health and longevity, and loneliness with poorer health.
Communication and relationships research — Research on listening, assertiveness, conflict and what keeps relationships healthy, from clinical and social psychology.
Sleep and circadian research — Research on the body clock, the role of light, caffeine and alcohol, and on cognitive behavioural therapy for insomnia (CBT-I), which guidelines recommend as a first treatment for chronic insomnia.
Exercise and health research — Research on physical activity and health, including large reviews showing exercise can reduce symptoms of depression and anxiety.
Nutrition research — Research on diet and health, including early trials on diet and mood and studies on ultra-processed food — an active area where many questions remain open.
Resilience research — Research by Ann Masten, George Bonanno and others showing resilience is common — “ordinary magic” — and built from relationships, skills and circumstances.
Gratitude, purpose and wellbeing research — Research on gratitude practices, purpose in life and wellbeing. Effects are usually modest and depend on how genuinely people take part.
Self-efficacy research — Albert Bandura’s research on how belief in your ability to do something grows mainly from doing it.
Growth mindset research — Carol Dweck’s work on beliefs about ability, and later large studies and reviews that found smaller and more variable effects of mindset interventions than first reported.
Evidence-based medicine and critical appraisal — The discipline of judging health claims: study designs, bias, correlation versus causation, and how strong evidence is built.
Social determinants of health research — Public-health and sociological research showing that income, education, work, housing, community and culture shape health as much as individual choices.