Part 5: The Body that Reads Signals

Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.

• For insomnia, start with what works

  The American College of Physicians recommends cognitive behavioral therapy as the first treatment for chronic insomnia. Melatonin is not recommended for it in adults.

  Topic 23

• Get children outdoors about two hours a day, with a floor of one

  Two hours was Taiwan's school target and is widely endorsed. China's plan specifies one to two, and the US National Academies at least one.

  Topic 24

• Get eyes checked

  Vision screening at least once between ages 3 and 5, an eye examination before first grade, and sooner if a child squints at distance.

  Topic 24

• If a child is already myopic and getting worse, ask about myopia control

  The US Food and Drug Administration authorized the first myopia-control spectacle lenses in September 2025, for children 6 to 12, citing 71% less progression over two years.

  Topic 24

• Adults with high myopia, know the warning signs

  A burst of new floaters, flashes of light, or a dark curtain across your vision means a same-day visit to an eye doctor or emergency room.

  Topic 24

• Learn the exchange rate

  Eight hours at 85 dBA, four at 88, one at 94, about 15 minutes at 100. If you have to raise your voice to be heard at arm's length, treat the time as short and leave before the...

  Topic 26

Good observational evidence with a plausible mechanism, or small or few trials.

• Get outside early

  Daylight in the first hours after waking, and at least 250 melanopic lux at the eye through the day (light weighted for its effect on melanopsin).

  Topic 23

• Dim the last three hours, and sleep in the dark

  Below about 10 melanopic lux in the evening and 1 in the bedroom. Sensitivity varies fiftyfold, so judge by your own sleep.

  Topic 23

• Keep the timing regular, weekends included

  Regularity predicted mortality better than duration in 60,977 people. Adults should aim for seven hours or more. A weekend outdoors pulls a late clock earlier (●○○).

  Topic 23

• Change screen habits, not lenses

  A device out of the bed and a cut-off time have better support than filters or blue-blocking glasses. Lower screen brightness does cut melatonin suppression in the laboratory.

  Topic 23

• Finish your shower cold for 30 to 90 seconds

  All three durations cut self-reported sickness absence equally in the one large trial. In open water, habituate and never swim alone (●○○).

  Topic 25

• Sauna: if you enjoy it, make it regular

  Practice in the Finnish cohort was about 79°C for about 14 minutes, four to seven times a week. Safety: no alcohol, involved in half of Finnish sauna deaths.

  Topic 25

• Hot baths, with Japanese caution

  Near-daily tub bathing tracked with lower cardiovascular risk in 30,076 Japanese adults, and a 40°C to 42.5°C bath one to two hours before bed shortens the time it takes to fall...

  Topic 25

• Get your hearing tested, and use aids if indicated

  Hearing loss is common and undertreated. Aids are reasonable, low-risk preventive practice, but the cognitive benefit in ACHIEVE was confined to a higher-risk subgroup.

  Topic 26

• Move the sound machine away from the crib

  If you use one, put it as far from the infant's head as the room allows, at the lowest volume and for the shortest time that works.

  Topic 26

• Make music with other people

  Sing, drum, dance in time with somebody. The proposed mechanism is synchrony plus exertion, and the practice costs nothing. A social good rather than a treatment.

  Topic 26

• About two hours a week in green or blue space (plants or water), in any pattern that suits you

  Parks, woodland, riversides and beaches all counted in the English survey behind the figure, whose design cannot prove direction.

  Topic 27

• If your mood is low, join something structured outdoors for 8 to 12 weeks

  Sixteen randomized trials pooled to better depressive mood and anxiety, with standardized effect sizes of -0.64 and -0.94, in sessions of 20 to 90 minutes.

  Topic 27

• Ask a clinician about a nature prescription

  Across 92 studies, mostly at moderate to high risk of bias, prescriptions were followed by systolic (upper) blood pressure about 4.8 mmHg lower and around 900 more steps a day...

  Topic 27

• For a street or a city, plant trees and green the vacant lots

  The one recommendation backed by natural experiments and a citywide randomized trial, and the only one that helps people who never read the advice (Chapter 45).

  Topic 27

• Enjoy forest bathing as relaxation , not as immune therapy

  Twenty trials put systolic pressure 3.15 mmHg lower in forest settings, mostly on the same day.

  Topic 27

Early, small, animal-only, or actively contested.

• Break up close work, and treat screen time mainly as indoor time

  Cohn's 15 minutes outdoors per hour of near work has never been tested on its own. The screen association cannot be separated from the room.

  Topic 24

• Let your rooms move a little

  Sit toward the cool end of comfort in winter, around 18°C to 19°C (64°F to 66°F), and add a layer rather than a degree. The supporting trials are tiny.

  Topic 25

• Use 60/60 as a heuristic, not a standard

  About 60% of maximum volume, about an hour at a time, then a break. No published research shows that following it prevents damage.

  Topic 26

• Build some real quiet into the day

  A stretch without engines, notifications or a screen playing to itself, ideally where you can hear weather and birds. The neurogenesis evidence is from mice.

  Topic 26

• Make each visit 20 to 30 minutes; 10 minutes still registers

  Leave the phone in your pocket, as the cortisol protocol did.

  Topic 27

• Put your desk where you can see something alive

  A 40-second view of a flowering green roof left 150 students making fewer errors than a view of bare concrete.

  Topic 27