Light exposure at night predicts incidence of cardiovascular diseases

https://www.medrxiv.org/content/10.1101/2025.06.20.25329961v1

by gnabgib • 1 year ago

124 114 1 year ago

medrxiv.org

patrickhogan1• 1 year ago

Each participant wore a wrist light tracker for 1 week.

ekianjo• 1 year ago

that seems very short

bracketfocus• 1 year ago

It is fairly short, but seems like enough time to get a baseline of habits across nearly 90,000 participants.

trollbridge13• 1 year ago

N>88,000, so it has a huge sample size. Most people have the same patterns of sleep and nighttime/daytime habits week to week.

cluckindan2• 1 year ago

Preprint not peer reviewed.

Also: ”A.J.K.P. and S.W.C. are co-founders and co-directors of Circadian Health Innovations PTY LTD.”

Lemme guess, looking for funding.

thimkerbell• 1 year ago

What can we do about the tendency of research articles to get their big flash of publicity before undergoing peer review?

cryptonector3• 1 year ago

We need to make it a lot cooler for researchers to not do original research all the time but to do replication and peer review. We should also demand publication of failures -- it's ok to fail, but only if you publish about the failure.

The whole publish-or-perish culture is a disaster that incentivizes cheating.

It should be considered just as valuable to have a few grad students working on replication as on original research, and that should not hurt the students' prospects.

kazinator2• 1 year ago

Stop reading non-peer-reviewed stuff and sharing links to it?

nudgeOrnurture2• 1 year ago

an active, public pre-review discussion. we nurture critical thinking before the nudge.

some charismatic, intelligent dude or dudette or couple with a curious but rather uneducated mind inviting grad students and scientists to discuss studies and pre-prints and so on, constantly babbling scientifically more or less correct nonsense but getting semantically corrected by the guests or something ... ... so viewers can feel "smartypants" and or relate and learn.

I'm sure there's podcasts but I don't listen to podcasts.

frtannar• 1 year ago

The best thing to do is to take commonly held knowledge and make a study out of it.

Maybe the next study could be “live king cobra in the bed results in sleep reduction”.

Probably a book and a TED talk to go with it.

roenxi• 1 year ago

Eh, you never know with studies. They did this one to serve as a classic counterexample: https://www.bmj.com/content/363/bmj.k5094

You can almost see the grin as they wrote up the results.

hammock• 1 year ago

So was Moderna? Means nothing

pazimzadeh4• 1 year ago

Peer review doesn't tell you if the data is valid or not. they published their methodology and anyone is free to repeat the study.

Peer review just checks for obvious errors in study design, asks for more info if needed, and decides whether the paper is a good fit for the journal.

Watson and Crick's paper describing the structure of DNA wasn't peer reviewed. if you think they're wrong, try it for yourself and publish the results.

When a few groups all get the same result then you can be confident about the claims made. until then, it's just kind of interesting to think about, which is fine.

A.J.K.P. and S.W.C. are co-founders and co-directors of Circadian Health Innovations PTY LTD

I do agree that this paper alone should not be used to help sell a product. But it looks like this paper just confirms previous findings using more rigorous methodology (see background):

"Light at night causes circadian disruption, (21–23) and is therefore a potential determinant of cardiovascular disease risk. Higher risks for coronary artery disease (24) and stroke (25) have been observed in people living in urban environments with brighter outdoor night light, as measured by satellite. Brighter night light has been cross-sectionally related to atherosclerosis, (26,27) obesity, hypertension, and diabetes (28) in small but well-characterized cohorts, using bedroom (26,27) and wrist-worn (28) light sensors. Moreover, experimental exposure to night light elevates heart rate and alters sympathovagal balance. (29) However, current evidence linking night light with cardiovascular risk is mostly within small cohorts, or relies on geospatial-level measurements of outdoor lighting, rather than measures of personal light exposure. (30,31)"

Dylan168072• 1 year ago

Peer review doesn't tell you if the data is valid or not.

Sure but nobody claimed that.

Watson and Crick's paper describing the structure of DNA wasn't peer reviewed.

I'd point out that outliers exist but that was before peer review become so popular.

Right now there's a good correlation between competency and peer review.

if you think they're wrong, try it for yourself and publish the results.

Watson and Crick or the article?

For a balanced discussion of the article, it's reasonable to point out a lack of peer review to give context to what stage this is at. If "try it yourself" is the bar then I guess nobody comments? That doesn't seem like a good way to learn anything.

renmillar2• 1 year ago

This creates a perfect setup for manipulation - the high barriers to entry for proper equipment, organization, and funding needed to produce quality reproductions mean that if someone posts fake content that mimics scientific paper formatting and includes all the right academic signals, most people will accept it as legitimate without question.

dotancohen2• 1 year ago

  > Also: ”A.J.K.P. and S.W.C. are co-founders and co-directors of Circadian Health Innovations PTY LTD.”

The other edge of the "not impartial" sword: these are people who are highly familiar, likely experts, in the related field. Who else is more qualified to conduct such a study?

nurettin2• 1 year ago

Who else is more qualified to conduct such a study?

Whoever does not have a monetary interest in the studied subject is the one who is more qualified. Same with smoking related research, same with children's toy paint related research. But the third edge is: These are phases of fraud that societies go through. They will happen, some will think they are legit, some won't, they disappear into some third world country after taking their sum. It always works like that. And that's predictive science right there.

Llamamoe2• 1 year ago

The result is, however, consistent with existing science.

cluckindan2• 1 year ago

However, there is likely a correlation between nighttime light exposure and living in a city, on a lower floor, next to a street with medium or heavy traffic.

There is likely also a significant correlation between living in such conditions and exposure to pollution, especially inhaled particulate matter.

Such a correlation also holds elsewhere: living in a high-rise means no streetlights outside your window, and also yields cleaner air than living at or near street level; living in the countryside means practically no light pollution, but also much less traffic and thus much less particulates in the air.

Inhaled particulate matter is a leading cause of cardiovascular disease.

See e.g. https://www.sciencedirect.com/science/article/pii/S073510971...

croes2• 1 year ago

So use the toilet in the dark?

_heimdall• 1 year ago

Do you have to turn the light on to use the toilet?

joe_the_user• 1 year ago

No but I think many people in fact turn the light on when using the toilet.

Krasnol2• 1 year ago

I do have to, this is why I bought one of those IKEA smart bulbs and made it dark and blue. If I get up at night, I use my watch for light.

kwertyoowiyop• 1 year ago

Gotta look for large spiders under the seat.

goopypoop• 1 year ago

Do you have to leave the bed?

trollbridge13• 1 year ago

I've always wondered about people who say that... there's enough light (particularly when it's not a new moon) to see to go the bathroom, but maybe my eyes adjust to the light better?

croes2• 1 year ago

Unless you use shutters so the room is completely dark

bregma2• 1 year ago

You must live in the city.

greenavocado• 1 year ago

Red light

schrodinger2• 1 year ago

I use iPhone flashlight on mild mode…

lazyeye• 1 year ago

Buy one of those darkness-sensing nightlight plugs and leave it in the bathroom. They cost under a $1 a month to run.

lunarcave• 1 year ago

including physical activity, smoking, alcohol, diet, sleep duration, socioeconomic status, and polygenic risk

Wondering how much of this is due to geography and air quality. City centers have relatively bad air quality and a high amount of ambient lighting at night, compared to non urbanized areas.

The cardiovascular effects of poor air quality is arguably well understood.

danielschreber• 1 year ago

My bet is that cardiovascular problems cause light exposure at night.

renmillar2• 1 year ago

Almost believable. You'd probably instinctively want fresh air when your heart's acting up.

trollbridge13• 1 year ago

Most studies pull from urban populations and usually contrasting with a rural population is done for a demographic comparison. (Most people also live in cities.) The study was careful to use personal light monitoring, so urban residents who nonetheless find ways to live/sleep in the dark would be included in the study.

lowwave• 1 year ago

> including physical activity, smoking, alcohol, diet, sleep duration, socioeconomic status, and polygenic risk And also light at night inhibits melatonin production. That along should already be able to lead to all kinds of healthy issues.

ethan_smith• 1 year ago

The study measured personal light exposure via wrist-worn trackers for a week rather than using geographic light pollution data, which would better control for the urban air quality confounding you've identified.

lo0dot0• 1 year ago

No, measuring light doesn't remove the air quality confounder. Measuring air quality would allow to remove the air quality confounder. What are you smoking?

patrakov3• 1 year ago

Sorry for exposing my personal medical data, but... I literally cannot fall asleep without at least some light. So I sleep with lights on. Trying to be like normal people would only make my overall health worse.

Is this a medical condition that has a name?

1oooqooq• 1 year ago

does it make a difference if it's warm or blue light?

patrakov3• 1 year ago

I think it doesn't make any difference. Back in Russia, I used 2700K or 3000K LEDs. Here in the Philippines, high-CRI warm-color LEDs are unobtainable, and the culture exhibits a nearly-universal shift to 6500K indoor lights (unlike in Europe), so I use 6500K, just like everyone else here. It still works.

lr4444lr• 1 year ago

Nyctophobia.

codingrightnow• 1 year ago

Maybe they're exposed to light at night because they're awake at night more often, possibly shift workers, which we already know is unhealthy. I doubt just having light on is causing the effect.

giraffe_lady2• 1 year ago

Yes they tracked hours of light exposure (above some threshold? I don't see that they say.) and found this result in the 90-100th percentile. So almost certainly night shift workers.

Buttons840• 1 year ago

Maybe got one of those lights that slowly dim to simulate sunset. You can fall asleep in the light, but it will be dark while you sleep. I have 2 Philips branded ones that have worked well for 11 years now.

Jensson• 1 year ago

If you are from a cold area people needed to keep a camp fire alive throughout the night or they died, I'd bet those would have a hard time sleeping without lights on since their ancestors who did died.

DNA adapts very quickly to such hard selectors, and many populations has lived in such areas for many thousands of years by now.

schrodinger2• 1 year ago

Vampirism.

mpnsk1• 1 year ago

Have you tried exposing yourself to an hour or two of darkness before you sleep?

timonoko• 1 year ago

If you live above 60 parallel, the night light is associated with summer. I also sleep with lights on, because dreams are about summer and happiness.

Worst thing is to wake up in total darkness in strange place. You dont remember were things are, cannot find the light switch, and start panicking, maybe I am gone blind?

etimberg• 1 year ago

Is this detecting people who work overnights?

loeg• 1 year ago

Almost certainly some kind of 3rd variable, yeah.

giraffe_lady2• 1 year ago

I believe so yes. They tracked hours of light exposure at night over a week, and found this result in the 90-100th percentile. The 90th percentile here is pretty much going to be people working at night yeah.

trollbridge13• 1 year ago

The percentiles of 50-60, 60-70, 70-80, and 80-90, however, are obviously not shift workers (unless they're shift workers working in the dark); you compare the lowest percentile of daylight light exposure to the highest percentile of nighttime light exposure, and see that there just aren't that many shift workers present in the study. About 13% of the UK population is considered to be nighttime workers. We can safely assume nighttime workers aren't represented in the 50%-90% percentile, because there simply aren't enough of them to go around, and would not be statistically significant.

readthenotes1• 1 year ago

If the article had said regularly having to go to work before 9:00 a.m. predicts incidence of cardiovascular disease, would we be having the same conversation?

trollbridge13• 1 year ago

Good catch, although there are plenty of studies and even metastudies on that topic (eg https://pmc.ncbi.nlm.nih.gov/articles/PMC11129786/ ); generally speaking, the healthiest people are those who work "normal" day shifts with "normal" hours (full time; not part time; no overtime).

3eb7988a1663• 1 year ago

Isn't that just a rough proxy for wealth? Outside of the coke-fueled hedge fund manager, the poor are more likely to have over-time/shift-work/irregular work hours. Your standard office drone can have a consistent work/sleep schedule.

Sporktacular• 1 year ago

Couldn't find the actual light levels associated with relative most/least bright.

softgrow• 1 year ago

It's in Table 1, of the paper. The "safe" night-time level for the bottom 50% of the population is surprising low, 0-1.21 lux. I've been sleeping for years with 10-20 lux (inner city, blinds open so I can enjoy the city lights). Maybe I'll need to close the blinds?

trollbridge13• 1 year ago

It's listed right in there. Search for "lux".

cjensen• 1 year ago

Under the "adjusted for established risk factors" they do not list an adjustment for age. I don't understand that -- doesn't age also correlate with insomnia frequency and cardiovascular disease?

alister• 1 year ago

Several comments here mentioned shift work as a possible explanation.

The paper concedes that shift work is unhealthy[1] but claims that shift work doesn't explain their finding[2]. And their conclusion is "avoiding night light may be a promising approach for preventing cardiovascular diseases," but without telling us why. It's going to be fascinating if there's a mechanism by which sleeping with light can cause heart disease.

[1] "Evidence demonstrates higher risks of adverse cardiovascular events, coronary heart disease, heart failure, atrial fibrillation, and mortality due to cardiovascular disease in rotating shift workers."

[2] "Following separate adjustments for pre-existing diabetes, hypertension, high BMI, high cholesterol ratio, short, long, or inefficient sleep, and exclusion of shift workers, the relationships of night light with cardiovascular risks were attenuated but remained statistically significant for all outcomes except stroke."

WD-101000• 1 year ago

It's going to be fascinating if there's a mechanism by which sleeping with light can cause heart disease.

I suspect everyone in the field already knows the top-level answer: light at night blunts the output of the circadian pacemaker (SCN), with all sorts of downstream effects including control of various hormones. So the levels will be different with light at night. "at night" means biological night. If someone consistently sleeps on some schedule with bright enough light during their awake time, and it's dark during their sleep time, it's fine.

I'm not in the field. I read up on it at one point at a shallow level and talked to some researchers about it informally.

idiotsecant• 1 year ago

I would make the comment about correlation and causation but I don't think it matters.

trollbridge13• 1 year ago

The study is claiming correlation.

bilsbie• 1 year ago

That sucks I keep a lamp on when I sleep.

ziofill• 1 year ago

How do they know the causal link? Can it be that people who stay up late sleep less and this causes issues, and there being light is only a consequence of staying up late?

circularfoyers• 1 year ago

These relationships were robust after adjusting for established risk factors for cardiovascular health, including physical activity, smoking, alcohol, diet, sleep duration, socioeconomic status, and polygenic risk.

There's more details further in the article[1].

[1] https://www.medrxiv.org/content/10.1101/2025.06.20.25329961v...

ltbarcly32• 1 year ago

It does not claim a causal link, just correlation.

trollbridge13• 1 year ago

"Correlation is not causation!" is one of the sillier things that people say when a study comes out with meaningful, interesting data. If nobody ever finds correlations in the first place, then it won't be possible to figure out causation - and we certainly do want to eventually find more causation for things like heart attacks, don't we?

jillesvangurp3• 1 year ago

Correlation is not the same as causation. The research indicates a correlation. Assuming causation is a classical mistake with any research.

In any case, light sensitivity and sleep patterns are well linked. If you live far away from the equator, you are dealing with pretty short nights half of the year. I lived in Helsinki for a while. That can really mess up your sleep though some people manage to adapt. There's a reason coffee is popular in places like

I currently live in Berlin. I sleep about 2-3 hours less in the summer than in the winter. Somehow that works for me. But it's really annoying to be wide awake at 6 when you've set your alarm for 8. I'm literally typing this on my laptop early morning on a Sunday. But it's light very early this time of year.

I've experimented with wearing sleep masks. They really work. But I find them slightly uncomfortable. What works better is just doing sane things like trying to live healthy. Less alcohol, more sport. Etc. Work stress can cause all sorts of issues with that.

jajko• 1 year ago

I sleep about 2-3 hours less in the summer than in the winter.

That's not OK, I don't know a single person affected so (live in cca same latitude as Berlin). Have you tried some radical solutions like good window blinds or similar sun blocking mechanisms? I don't mean some cheap crap that still lets strips of light through, I mean full block. Of course if then some chopper or ambulance wakes you up regardless it doesn't matter.

tuukkah2• 1 year ago

In addition, seasonal disorders are equally common in Madrid and Helsinki, so that cannot explain any difference in sleep disorders.

Btw, did you take a D vitamin supplement and use a light therapy lamp in the mornings?

kazinator2• 1 year ago

Is this light exposure imposed by the experiment on random subjects, or is it something coming from their lifestyle?

perilunar• 1 year ago

As an inveterate night owl these sorts of results bother me, but if I try to force myself to sleep and wake earlier I feel like shit. Better to listen to my own body than do something because of a population-wide correlation I guess. Or hope, anyway.

nudgeOrnurture2• 1 year ago

Incidence of coronary artery disease, myocardial infarction, heart failure, atrial fibrillation, and stroke
People with the brightest nights (90-100th percentiles) had significantly higher risks of developing coronary artery disease (adjusted-HR range: 1.23-1.32), myocardial infarction (aHRs: 1.42-1.47), heart failure (aHRs: 1.45-1.56), atrial fibrillation (aHRs: 1.28-1.32), and stroke (aHRs: 1.28-1.30), compared to people with dark nights (0-50th percentiles).
These relationships were robust after adjusting for established risk factors for cardiovascular health, including physical activity, smoking, alcohol, diet, sleep duration, socioeconomic status, and polygenic risk. Relationships of night light with risk of heart failure and coronary artery disease were stronger for women, and relationships of night light with risk of heart failure and atrial fibrillation were stronger for younger individuals in this cohort.

These relationships were *robust*.

The observed associations between nighttime light exposure and increased incidence of coronary artery disease, myocardial infarction, heart failure, atrial fibrillation, and stroke may be driven by complex and multifactorial pathways. These cardiovascular conditions can arise from numerous interrelated long- and short-term physiological and behavioral factors, making it difficult to isolate the causal role of nighttime light exposure alone.

It is plausible to hypothesize that if individuals in the lower-exposure group were subjected to increased nighttime light exposure under controlled conditions—where all other lifestyle factors remained constant and stress levels were actively managed—their cardiovascular risk might not increase. This would suggest that ambient light exposure at night, in isolation, may not be a direct etiological factor.

Although the study adjusted for a broad range of established cardiovascular risk factors—including physical activity, smoking, alcohol consumption, diet, sleep duration, socioeconomic status, and polygenic risk—these adjustments do not capture acute or chronic variations in psychological stress. Since stress is a known contributor to cardiovascular disease, the inability to directly account for its temporal dynamics represents a potential limitation in the interpretation of these findings.

jamesholden• 1 year ago

What about all the people that live in the North, like Finland, etc?

pwdisswordfishz• 1 year ago

Did they control for coffee drinking?

seydor• 1 year ago

but i leave only my screen on

dubeye• 1 year ago

I thought this was well established?

My cardiologist always asks about sleep, isn't it obvious a darker room makes for better sleep

bregma2• 1 year ago

I do not have sleep problems. I can sleep anywhere, light or dark. It is completely obvious to me that ambient light and sleep are uncorrelated in any way.

amelius• 1 year ago

Makes sense, people who work late tend to be more stressed.

trollbridge13• 1 year ago

Only 13% of the population works nights, yet people with high levels of exposure to light at night were far more than 13% of the sample.

Light exposure at night predicts incidence of cardiovascular diseases

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