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)"
> 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?
> 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.
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.
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.
>> 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.
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.
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.
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?
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.
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?
> 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.
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.
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?
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."
> 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.
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.
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.
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?
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).
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.
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?
> 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.
[+] [-] cluckindan|8 months ago|reply
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.
[+] [-] pazimzadeh|8 months ago|reply
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)"
[+] [-] frtannar|8 months ago|reply
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.
[+] [-] thimkerbell|8 months ago|reply
[+] [-] dotancohen|8 months ago|reply
[+] [-] Llamamoe|8 months ago|reply
[+] [-] hammock|8 months ago|reply
[+] [-] lunarcave|8 months ago|reply
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|8 months ago|reply
[+] [-] danielschreber|8 months ago|reply
[+] [-] ethan_smith|8 months ago|reply
[+] [-] lowwave|8 months ago|reply
[+] [-] patrakov|8 months ago|reply
Is this a medical condition that has a name?
[+] [-] Buttons840|8 months ago|reply
[+] [-] timonoko|8 months ago|reply
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?
[+] [-] mpnsk1|8 months ago|reply
[+] [-] codingrightnow|8 months ago|reply
[+] [-] lr4444lr|8 months ago|reply
[+] [-] schrodinger|8 months ago|reply
[+] [-] 1oooqooq|8 months ago|reply
[+] [-] ziofill|8 months ago|reply
[+] [-] circularfoyers|8 months ago|reply
There's more details further in the article[1].
[1] https://www.medrxiv.org/content/10.1101/2025.06.20.25329961v...
[+] [-] jillesvangurp|8 months ago|reply
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.
[+] [-] ltbarcly3|8 months ago|reply
[+] [-] cjensen|8 months ago|reply
[+] [-] alister|8 months ago|reply
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|8 months ago|reply
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.
[+] [-] perilunar|8 months ago|reply
[+] [-] patrickhogan1|8 months ago|reply
[+] [-] ekianjo|8 months ago|reply
[+] [-] etimberg|8 months ago|reply
[+] [-] giraffe_lady|8 months ago|reply
[+] [-] loeg|8 months ago|reply
[+] [-] readthenotes1|8 months ago|reply
[+] [-] trollbridge|8 months ago|reply
[+] [-] dubeye|8 months ago|reply
My cardiologist always asks about sleep, isn't it obvious a darker room makes for better sleep
[+] [-] bregma|8 months ago|reply
[+] [-] bilsbie|8 months ago|reply
[+] [-] Sporktacular|8 months ago|reply
[+] [-] softgrow|8 months ago|reply
[+] [-] trollbridge|8 months ago|reply
[+] [-] nudgeOrnurture|8 months ago|reply
> 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.
[+] [-] kazinator|8 months ago|reply
[+] [-] jamesholden|8 months ago|reply
[+] [-] amelius|8 months ago|reply
[+] [-] pwdisswordfishz|8 months ago|reply
[+] [-] idiotsecant|8 months ago|reply
[+] [-] seydor|8 months ago|reply