Light exposure at night predicts incidence of cardiovascular diseases
62 comments
·July 12, 2025cluckindan
pazimzadeh
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)"
Dylan16807
> 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.
frtannar
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
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.
thimkerbell
What can we do about the tendency of research articles to get their big flash of publicity before undergoing peer review?
cryptonector
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.
zer00eyz
> 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.
This should be the work of grad students, not cranking out another paper or slaving for professors.
> We should also demand publication of failures -- it's ok to fail, but only if you publish about the failure.
I really want to have a journal that just publishes interesting duds. Someone else might look at your methodology and get their own idea.
kazinator
Stop reading non-peer-reviewed stuff and sharing links to it?
hammock
So was Moderna? Means nothing
ziofill
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
> 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...
ltbarcly3
It does not claim a causal link, just correlation.
lunarcave
> 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.
trollbridge
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.
danielschreber
My bet is that cardiovascular problems cause light exposure at night.
patrakov
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?
timonoko
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?
Buttons840
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.
mpnsk1
Have you tried exposing yourself to an hour or two of darkness before you sleep?
codingrightnow
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_lady
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.
schrodinger
Vampirism.
lr4444lr
Nyctophobia.
1oooqooq
does it make a difference if it's warm or blue light?
patrakov
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.
xattt
6500k? Deliberately in the home??
Is this one of those things where some element is considered desirable in the Western world (e.g. warm white lighting) but is associated with destitution in another culture (because it’s like incandescent lighting)?
cjensen
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?
perilunar
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.
alister
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
> 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.
etimberg
Is this detecting people who work overnights?
loeg
Almost certainly some kind of 3rd variable, yeah.
giraffe_lady
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.
kazinator
Is this light exposure imposed by the experiment on random subjects, or is it something coming from their lifestyle?
patrickhogan1
Each participant wore a wrist light tracker for 1 week.
ekianjo
that seems very short
bracketfocus
It is fairly short, but seems like enough time to get a baseline of habits across nearly 90,000 participants.
bilsbie
That sucks I keep a lamp on when I sleep.
Sporktacular
Couldn't find the actual light levels associated with relative most/least bright.
softgrow
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?
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.