Morning light

Do this

• Go outside within 30–60 minutes of waking. A balcony or an open car window counts. Glass blocks too much, so don't rely on a closed window.
• Face the bright part of the sky without sunglasses. Look toward the low sun, never straight at it.
• Stay about 5–10 minutes on a clear morning and 15–20 or more under cloud. These durations come from his earlier published guidance; he gives no minutes in this episode.
• Up before sunrise? Use a 10,000 lux lamp until daylight arrives.
• Missed a day? Stay out about twice as long the next morning.
• Two or three times a week, also get low-UV sun on your skin.

Why it works

Light-sensitive cells in the retina report daylight to the brain's master clock. Bright light in the first hour pushes the morning cortisol peak higher, and a higher morning peak sets up lower cortisol and earlier melatonin at night. Phone and laptop screens are too dim to do this job in the morning, yet bright enough to disturb the clock at night.

What the research says

The strongest of the ten. Light is the main signal that sets the human body clock, and two very large wearable-sensor studies link bright days and dark nights to better mental health and longer life. Those large studies are observational, so they show association and not proof of cause.

• Leproult et al., Journal of Clinical Endocrinology & Metabolism, 2001Transition from dim to bright light in the morning induces an immediate elevation of cortisol levelsMoving from dim to bright light in the early morning raised cortisol by more than 50% in sleep-deprived volunteers. The same change in the afternoon did nothing.
• Windred et al., PNAS, 2024Brighter nights and darker days predict higher mortality risk: A prospective analysis of personal light exposure in >88,000 individualsAbout 89,000 UK Biobank adults wore light sensors for a week. The brightest nights went with 21–34% higher risk of death in the following years, the brightest days with 17–34% lower risk.
• Burns et al., Nature Mental Health, 2023Day and night light exposure are associated with psychiatric disorders: an objective light study in >85,000 peopleIn the same cohort, more light at night went with more depression and anxiety, and more light by day with less.
• Lindqvist et al., Journal of Internal Medicine, 2016Avoidance of sun exposure as a risk factor for major causes of death: a competing risk analysis of the Melanoma in Southern Sweden cohortSwedish women who avoided the sun lived shorter lives than those who sought it. This is the source of his remark about smokers and sunlight. Observational and open to confounding.
• Powner & Jeffery, Journal of Biophotonics, 2024Light stimulation of mitochondria reduces blood glucose levelsFifteen minutes of 670 nm red light on the back cut the two-hour blood sugar rise after a glucose drink by 27.7% and the peak by 7.5%, in 30 healthy adults. The episode describes this as more than 25% off the peak, which overstates the peak figure.

Watch out

Never stare at the sun, and stop if your eyes hurt. Check the UV index before exposing skin, and follow your dermatologist's advice if you have a history of skin cancer. Some medications and eye conditions make bright light risky.