What the evidence actually says

One question per page, read against the research, with a plain verdict on how much weight it holds.

31 questions · 6 capabilities · 57 sources read and checked · 9 verdicts the evidence firmly supports

Does willpower actually run out?The evidence says no. A preregistered test across 36 laboratories and 3,531 participants found an ego depletion effect of d = 0.06, which is indistinguishable from zero, and the Bayesian analysis found the data four times more likely under the null. The original literature reported d = 0.62, and publication bias explains most of that gap. Willpower behaving like a fuel tank is a metaphor rather than a finding.

Strength of evidence

  1. traditional
  2. emerging
  3. informed
  4. established
1 source checked · reviewed 17 August 2026
How do you actually lower cortisol?

Strength of evidence

evidence-based

Does sleep hygiene actually work?

Strength of evidence

evidence-based

Every brief carries its weight on the page

Nothing here is graded by how much we like it. Each question is read against the studies, then labelled with how much the evidence will actually bear.

evidence-based
Supported by controlled trials or meta-analysis, replicated by more than one research group.
evidence-informed
Real signal in the research, with small studies, small effects, or few controls holding it back.
emerging
Early findings that look promising and need better studies before anyone can be sure.
traditional
Long practised in a living tradition, with limited clinical study behind it.

Three more labels cover ideas whose meaning sits outside experimental trials. This keeps philosophy and metaphor in their proper category.

How we grade the evidence

Browse by capability

Six capabilities of mental longevity. Open one to read every brief in it.

Cognitive clarityFocus, attention, and memoryEmotional regulationStress and calmPsychological flexibilityLearning and adaptingIntentional behaviorHabits and follow-throughSocial connectionRelationships and purposeRestoration capacitySleep, rest, and recovery

Latest briefs

Does meditation work, and what for?Mindfulness meditation has moderate evidence for anxiety, depression and pain, with small effect sizes between 0.22 and 0.40. Evidence was low for stress and mental health quality of life, and low or insufficient for mood, attention and weight. Mantra meditation showed no effect on anything measured. No meditation programme outperformed the established therapies it was compared against.

Strength of evidence

evidence-informed

1 source checkedDoes being bilingual protect the brain?Bilingual people present with dementia symptoms roughly four and a half years later than monolinguals, replicated in India, Belgium and China. They do not develop less disease. Prospective studies find no difference in whether Alzheimer's occurs, and bilinguals tolerate more visible damage before symptoms appear. Reserve delays the symptoms and does not prevent the pathology.

Strength of evidence

evidence-informed

1 source checkedDoes volunteering actually help you live longer?The association is real and conditional. Following 10,324 older adults for nearly eleven years, volunteering was associated with a 19 per cent lower risk of death among able-bodied people. Among people with disabilities there was no survival advantage at all, and across the whole sample the effect fell just short of significance. That split is the most informative part of the finding.

Strength of evidence

evidence-informed

1 source checkedDoes willpower actually run out?The evidence says no. A preregistered test across 36 laboratories and 3,531 participants found an ego depletion effect of d = 0.06, which is indistinguishable from zero, and the Bayesian analysis found the data four times more likely under the null. The original literature reported d = 0.62, and publication bias explains most of that gap. Willpower behaving like a fuel tank is a metaphor rather than a finding.

Strength of evidence

evidence-based

1 source checkedDoes magnesium help you sleep?Possibly, by a small margin, on weak evidence. Pooling three randomised trials of 151 older adults, magnesium reduced time to fall asleep by 17.4 minutes against placebo. Total sleep time rose by 16 minutes and did not reach significance. Every trial carried moderate to high risk of bias and the authors graded the evidence low to very low.

Strength of evidence

emerging

1 source checkedHow do you actually lower cortisol?Movement lowers cortisol, and the type and amount both matter. Across 44 randomised trials covering 3,284 distressed people, yoga produced the largest reduction at SMD −0.59, with qigong second. The relationship followed an inverted U, peaking around 530 MET-minutes a week, roughly 90 to 150 minutes of moderate activity. High-intensity interval training tended to raise cortisol instead.

Strength of evidence

evidence-based

1 source checked

What we mean by mental longevity

Mental longevity is the lifelong capacity to think clearly, regulate your inner state, adapt to change, keep learning, maintain meaningful connections, and live intentionally.

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