Study finds bright nights raise risk for stroke and heart failure in adults over 40

 In your hospital, has your incompetent? doctor ensured night lighting is low enough?

 This just proves everyone's incompetence if nothing was done with any of this research!

Light exposure linked to mortality risk November 2024

Do you prefer your doctor, hospital and board of director's incompetence NOT KNOWING? OR NOT DOING?

Study finds bright nights raise risk for stroke and heart failure in adults over 40

Researchers have discovered that people exposed to brighter light at night face up to 50% higher risks of heart disease, while daytime light may protect the heart by reinforcing healthy circadian rhythms.

Study: Light Exposure at Night and Cardiovascular Disease Incidence. Image Credit: Krakenimages.com / Shutterstock

In a recent study published in JAMA Network Open, researchers explored whether being exposed to light at nighttime is associated with a higher risk of developing heart disease, particularly for those of a specific age, sex, or genetic makeup.

Their findings indicate that people over 40 exposed to bright lights at night face higher risks of heart disease, including stroke and heart failure. Associations were larger in females for heart failure and coronary artery disease, and in younger participants for heart failure and atrial fibrillation, with no clear modification for myocardial infarction or stroke.

Background

Healthy cardiovascular function relies on well-regulated circadian rhythms, which in turn influence vascular function, glucose tolerance, hormone levels, blood pressure, and heart rate. Disruption of these rhythms, through exposure to light or irregular sleep patterns, can elevate blood pressure and heart rate, increase inflammation, and reduce heart rate variability.

Animal studies show that prolonged circadian disruption can cause structural heart changes, such as hypertrophy and fibrosis. It worsens heart failure. Epidemiological evidence also links shift work, which disturbs these rhythms, to greater cardiovascular mortality, coronary heart disease, and heart failure.

Light exposure at night is a key source of circadian disruption and has been linked to higher rates of coronary artery disease and stroke, as well as conditions like obesity, diabetes, and hypertension, which are known cardiovascular risk factors. However, previous studies often relied on satellite-based measures of outdoor lighting or on small cohorts rather than on direct personal light-exposure data.

Using wrist-worn light sensors from about 89,000 UK Biobank participants, earlier research found that brighter nights were associated with higher cardiometabolic mortality and type 2 diabetes. Building on this, the present study examined whether individual day and night light exposures predict incident cardiovascular diseases over 9.5 years of follow-up.

About the Study

This large-scale cohort study used data from UK Biobank participants who wore wrist-worn light sensors for one week between 2013 and 2016. Participants’ light exposure was recorded continuously, processed to remove invalid data, and averaged into 24-hour profiles.

Factor analysis identified two main exposure periods: daytime (7:30 AM–8:30 PM) and nighttime (12:30 AM–6:00 AM). Participants were categorized into light-exposure percentiles, with the 0–50th percentile representing the darkest nights.

Cardiovascular outcomes, including stroke, atrial fibrillation, heart failure, myocardial infarction, and coronary artery disease, were identified using hospital, primary-care, and death-registry records. Individuals with pre-existing cardiovascular disease (CVD) were excluded.

Cox proportional-hazards models assessed the relationship between light exposure and disease risk, adjusting sequentially for demographic factors (ethnicity, age, and sex), socioeconomic variables (deprivation, education, and income), and lifestyle factors (urbanicity, diet, alcohol, smoking, and physical activity). Additional models were tested for potential interactions with genetic risk scores, age, and sex.

Key Findings

Researchers analyzed data from 88,905 UK Biobank participants, with an average age of 62.4 years and 57% female, over an average follow-up of 7.9 years. Participants were free of cardiovascular disease at baseline.

Nighttime light exposure showed a clear, dose-dependent association with a higher risk of heart disease, while daytime light exposure was linked to lower risks in minimally and socioeconomically adjusted models, but these associations were not significant after full lifestyle adjustment. When physical activity was excluded from the full model, inverse associations re-emerged for heart failure and stroke.

Compared with those in the darkest-night environment, participants with the brightest night exposure had significantly greater risks of coronary artery disease, myocardial infarction, heart failure, atrial fibrillation, and stroke after adjusting for lifestyle, demographic, and socioeconomic factors.

In contrast, an increase in night-light exposure by one standard deviation raised the risk of all five cardiovascular outcomes by about 5–8%. The associations were consistent across models and remained robust after adjustments. Sex and age showed selective modifying effects, with larger associations in females for heart failure and coronary artery disease, and in younger individuals for heart failure and atrial fibrillation, with no clear modification for myocardial infarction or stroke. Associations also remained after accounting for polygenic risk, suggesting gene–environment correlation is unlikely to explain the results.

Conclusions

This large prospective study demonstrates strong associations of higher nighttime light exposure with elevated cardiovascular risk, though causality cannot be inferred. The mechanisms underlying this association could include circadian disruption and sleep disturbance, leading to vascular and metabolic stress. Reduced melatonin secretion was not directly examined in this study.

In contrast, greater daytime light exposure may support cardiovascular health by reinforcing circadian rhythms.

Key strengths of this analysis include a large sample size, objective light measurements, and a long follow-up period. However, limitations include potential residual confounding, limited ethnic diversity (primarily White participants), lack of information on light sources, and the inability to infer causality. Sleep duration and efficiency were objectively measured and included in sensitivity analyses; short sleep partially attenuated some associations. Source information was unavailable, limiting the ability to adjust for behaviors correlated with light exposure.

Overall, these findings highlight artificial nighttime lighting as a potentially modifiable environmental risk factor for cardiovascular disease, underscoring the importance of maintaining dark nights and adequate daylight exposure in urban health strategies.

Journal reference:

• Windred, D.P., Burns, A.C., Rutter, M.K., Lane, J.M., Saxena, R., Scheer, F.A.J.L., Cain, S.W., Phillips, A.J.K. (2025). Light exposure at night and cardiovascular disease incidence. JAMA Network Open 8(10): e2539031. DOI: 10.1001/jamanetworkopen.2025.39031. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2840489

Light exposure linked to mortality risk

 

But should it be  one of these? Has your doctor incompetently done nothing with any of these?

• intermittent light exposure (1 post to March 2021)

• flickering light (3 posts to February 2020)

• bright light stimulation (1 post to April 2017)

• bright light therapy (2 posts to February 2017)

• bright lighting (1 post to April 2022)

• blue light (9 posts to February 2017)

• 60 Hertz flickering light (1 post to July 2021)

• 40 Hertz flickering light (1 post to July 2021)

• led lights (1 post to August 2017)

• light therapy (10 posts to December 2011) 

• light-activated therapy (1 post to October 2013)

• low-level laser/light therapy (3 posts to December 2014) 

• naturalistic light (2 posts to August 2019)

• near infrared light (5 posts to August 2015)

• sunlight (2 posts to December 2016)

• ultraviolet light (2 posts to May 2018)

Light exposure linked to mortality risk

Key takeaways:

• Those with the highest day light exposure had a 17% to 34% reduced mortality vs. those with the lowest.
• Earlier and later circadian phase and lower circadian amplitude also increased the risk for mortality.

Perspective from Roger Seheult, MD

Individuals experiencing more frequent exposure to light during nighttime hours may have a higher risk for death, results from a retrospective cohort analysis published in PNAS showed.

Meanwhile, researchers reported a converse link suggesting a decrease in mortality risk among those who had longer exposure to light during daytime hours.

Data derived from:  Windred D, et al. Proc Natl Acad Sci U S A. 2024;doi:10.1073/pnas.2405924121.

The findings support seeking day light and minimizing night light, the researchers noted.

The disruption of circadian rhythm from light exposure can lead to various negative health outcomes, Daniel P. Windred, from Flinders University in Australia, and colleagues wrote, but whether personal day and night light exposure could predict the risk for mortality has not been thoroughly assessed.

In the study, the researchers evaluated over 13 million hours of light exposure data recorded by wrist sensors worn byt 88,905 U.K. Biobank participants over the course of a week.

The analysis revealed 3,750 deaths in the study cohort over a follow-up period of 8 years, 798 of which experienced cardiometabolic deaths.

Windred and colleagues found that people in the 70^th to 90^th and 90^th to 100^th percentiles of night light exposure had a 15% to 17% and 21% to 34% increased risk for all-cause mortality, respectively, vs. those in the 0 to 50^th percentiles.

Meanwhile, those in the 70^th to 90^th percentile of night light exposure had a 22% to 26% increased risk for cardiometabolic morbidity vs. those with the lowest night light exposure, while those in the 90^th to 100^th percentile had a 33% to 46% increased risk.

The researchers explained that these findings may be due to night light exposure disrupting circadian rhythms, which could lead to cardiometabolic outcomes like stroke, diabetes and obesity and subsequently death.

They also pointed out that disrupted circadian rhythms predicted mortality, as each standard deviation reduction in circadian amplitude corresponded with a 4% to 10% higher risk for all-cause mortality risk and a 7% to 13% higher risk for cardiometabolic mortality.

People in the 50^th to 70^th, 70^th to 90^th and 90^th to 100^th percentiles of day light exposures had a 10% to 16%, 16% to 26% and 17% to 34% reduced risk for all-cause mortality, respectively, compared with those in the 0 to 50^th percentiles.

This relationship may be the result of the enhancing effects of day light on circadian rhythm, “which protect against the negative health effects of circadian disruption,” Windred and colleagues wrote.

“Co-occurrence of physical activity with day light exposure is another plausible explanation for relationships of day light with mortality risk,” they added.

The researchers acknowledged some study limitations. The study cohort comprised mostly white individuals — making the general applicability of findings’ to other diverse populations unclear — although it is possible the associations had unmeasured factors.

Ultimately, the data “demonstrate the importance of maintaining a dark environment across the late night and early morning hours, when the central circadian pacemaker is most sensitive to light, and seeking bright light during the day to enhance circadian rhythms,” Windred and colleagues wrote. “Protection of lighting environments may be especially important in those at risk for both circadian disruption and mortality, such as in intensive care or aged-care settings.”

Perspective

Back to Top

Roger Seheult, MD

I was pleasantly surprised [with the findings] because I thought that the results of the study confirmed everything that we’ve known. We’ve suspected for some time that, based on epidemiological data, light at night was bad because, among other things, it disrupts the circadian rhythm but also shuts down melatonin production from the pineal gland, which we known is beneficial as an antioxidant and other things. There’s also emerging evidence over the last decade that’s pretty strong [that shows] that sunlight during the day also has a lot of beneficial effects. What we didn’t have what was the individual, intervention prospective data that we have now have with this trial. What we had before was epidemiological data based on questionnaires and behavior. I think this is a step forward.

I believe that we need to advise our patients, especially those that are having some of these chronic illnesses that we’re seeing today and having difficulty with sleep, that they need to turn off lights after 9 o’clock and need to get outside and get as much light as possible. The reason why I say outside, even though the study investigators didn’t differentiate that — they just measured light — is that there is a tremendous [greater] magnitude of light outside than there is inside.

[W]ith any good study, there are more questions that are raised, and the same is true for this study. This study measured light that was coming through a wearable watch that they had for one week, and they were able to make these determinations from that one week. But what we don’t know is what type of light was doing the heavy lifting in terms of the mortality reductions during the day. Was it visible light, was it infrared light, was it ultraviolet light? That would go a long way to telling us what kind of behavior we [should be doing] because there’s a big difference between turning off the artificial lights in your house during the day and going outside into the sunlight. There’s a number of health reformers from the 19^th century that actually noticed this and commented on the benefits of sunlight during the day and turning off lights at night, so we’ve known about this for some time, but the science is catching up.

Light stimulation may help delay AD progression, more research needed in older adults

 But should it be  one of these? Has your doctor incompetently done nothing with any of these to prevent your likely dementia?

• intermittent light exposure (1 post to March 2021)

• flickering light (3 posts to February 2020)

• bright light stimulation (1 post to April 2017)

• bright light therapy (2 posts to February 2017)

• bright lighting (1 post to April 2022)

• blue light (9 posts to February 2017)

• 60 Hertz flickering light (1 post to July 2021)

• 40 Hertz flickering light (1 post to July 2021)

• led lights (1 post to August 2017)

• light therapy (10 posts to December 2011) 

• light-activated therapy (1 post to October 2013)

• low-level laser/light therapy (3 posts to December 2014) 

• naturalistic light (2 posts to August 2019)

• near infrared light (5 posts to August 2015)

• sunlight (2 posts to December 2016)

• ultraviolet light (2 posts to May 2018)

 

Your chances of dementia here. Hopefully your doctor knows this and has prepared prevention protocols.

1. A documented 33% dementia chance post-stroke from an Australian study?   May 2012.

2. Then this study came out and seems to have a range from 17-66%. December 2013.

3. A 20% chance in this research.   July 2013.

4. A 2-fold increase in dementia risk in this study    Jan. 2017 

 

Light stimulation may help delay AD progression, more research needed in older adults

SAN DIEGO — Light exposure and stimulation of the locus coeruleus may be a promising way to delay Alzheimer’s disease progression, according to a presenter at the Alzheimer’s Association International Conference.

“With light stimulation we try to target the locus coeruleus (LC), which has huge implications in earlier stages of Alzheimer’s disease,” Elise Beckers, of Limburg Alzheimer’s Centre at Maastricht University in the Netherlands, said during her poster presentation. “We also know the pupil is somehow linked to LC activity and that would be an easy readout, since the pupil is more easily accessible compared to the brain.”

Source: Adobe Stock.

Understanding the role of LC structure and function in the earliest stages of AD neuropathology and that light exposure may be a promising way to delay disease progression, Beckers and colleagues sought to characterize pupil responses to light during fMRI and determine its quality in assessing non-image forming effects of light.

Researchers continuously recorded pupil diameter in 16 healthy participants (11 women), aged 16 to 30 years, with an infrared eye-tracking device while they were given a 15-minute auditory oddball task in a 7T fMRI scanner. Participants were concurrently exposed to pseudo-randomly alternating 30- to 40-second blocks of polychromatic blue (4,000 K, 200 µW/cm²) and monochromatic orange (589 nm, 6 x 1,013 photons/cm²/s) lights.

Beckers and colleagues calculated pupil response as the average pupil size during the entire block of light, and used mixed-model analysis to determine the effects of light condition on pupil response, with participants as random intercept and controlling for age, sex and BMI.

Results showed that blue light was associated with a significantly smaller pupil diameter compared with orange light (main effect of light condition: F(2,270) = 571.22). The effect of the light condition on pupil size did not significantly change over the 15-minute protocol (light condition x block repetition interaction: F(12,240) = 1.21), suggesting that time-in-protocol and previous light blocks did not affect pupil constriction.

“With light stimulation, we could modulate LC activity ... and that will be an easy technique, easily accessible and easily handleable for AD patients in the future,” Beckers said.