Bright light Days, No light Nights leads to Longer Life

From NPR

I’ve been much more careful about light at night.  I now wear a sleep mask and it has increased my deep sleep by 42%.  YouTube on it here.

Huberman has advocated getting light first thing in the morning for years.  But in the write up below, they emphasize the enormous difference between having light inside versus outside.  They advocate morning and evening light at the transitions in the day if possible.  In Chinese Medicine, they advocate light in the middle of the day to get the most yang, so that you will activate the most yin for sleep.  It’s a durable concept in chinese medicine, of nurturing the yin to strengthen yang and vice versa.  Yet another scientific validation of Chinese Medicine principles.

Huberman spoke about light here. 

Scientists tracked nearly 90,000 people in the U.K. who spent a week with wrist-worn activity devices equipped with light sensors. Then, they analyzed their risk of dying over the next eight years. The results were published in the Proceedings of the National Academies of Sciences.

The study participants with the brightest nights had a 21% to 34% higher risk of premature death, compared to those who were mostly in the dark between midnight and dawn.

The results reflect decades of research indicating that our modern relationship to light can spell disaster for our circadian rhythms — the patterns in our physiology and behavior that fluctuate over the 24-hour cycle — influencing sleep, blood pressure, how we use energy, release hormones and countless other functions.

But even if you can’t pull that off, Windred says you will still reap the benefits of outdoor light later in the day. “If you come home from work in the afternoon and the sun is up, it’s still a good time to get light.”

In fact, Czeisler says people tend to underestimate the effects of being outside during dawn and dusk — times when you are being exposed to different wavelengths and intensities of light.

“We think that these transitions are probably particularly important,” he says. As long as there’s daylight though, he encourages people to get outdoors, ideally for at least half an hour to 45 minutes.

“It doesn’t have to be all at once,” he says, “This will do wonders for their health.”

D.P. Windred, A.C. Burns, J.M. Lane, P. Olivier, M.K. Rutter, R. Saxena, A.J.K. Phillips, S.W. Cain, Brighter nights and darker days predict higher mortality risk: A prospective analysis of personal light exposure in >88,000 individuals, Proc. Natl. Acad. Sci. U.S.A.
121 (43) e2405924121,
https://doi.org/10.1073/pnas.2405924121 (2024).

Summary of pnas paper here

This study explored how personal light exposure impacts mortality, analyzing data from ~89,000 UK Biobank participants aged 40 and older who wore light sensors for one week. Over an 8-year follow-up, 3,750 deaths were recorded. The findings showed that brighter daytime light exposure significantly reduced mortality risk (10% to 34%, depending on exposure levels), while brighter nighttime light increased mortality risk (15% to 34%). Circadian disruptions, such as lower circadian amplitude or misaligned phases, were also linked to higher mortality risks. The strongest associations were observed for cardiometabolic-related deaths.

The research underscores the importance of maintaining healthy light patterns to support circadian rhythms. Maximizing daytime light, minimizing nighttime light, and keeping consistent light–dark cycles are simple, cost-effective strategies to promote longevity and improve health outcomes, particularly for cardiometabolic health. These accessible interventions could help mitigate risks associated with circadian disruption.