Dim lights and dark environments: a highly economical strategy—and beneficial for health as well. Sleeping in darkness, according to a recent study published in JAMA Network Open, would save or at least reduce the risk of stroke and heart failure among adults over 40.
Nighttime Light Exposure
The data are broad and robust and would leave little room for misinterpretation: an analysis of more than 88,900 participants from the UK Biobank, with an average age of 62.4 years, 57% of whom were women, tracked for a mean of 7.9 years, healthy at baseline and without cardiovascular disease specifically, appears to show a clear dose–response association between nighttime light exposure and a higher risk of heart disease. In contrast, daytime light exposure correlated with lower risks in models that were minimally adjusted and adjusted for socioeconomic factors; associations that did not remain significant after full lifestyle adjustment. In general, the data would indicate that individuals exposed to brighter light at night are more susceptible to developing heart disease—up to about a 50% higher risk—compared with those exposed to daytime light, which can protect the heart by reinforcing healthy circadian rhythms.
That risk would be conditioned by several factors, including age — specifically over 40 — as well as sex, genetic background: a combination of components that would also determine a distinct risk profile: among women, heart failure and coronary artery disease, and among the younger participants, heart failure and atrial fibrillation, with no clear alterations for myocardial infarction or stroke.
The Basic Concept
A healthy cardiovascular function is linked to well-regulated circadian rhythms, which in turn influence vascular function, glucose tolerance, hormone levels, blood pressure, and heart rate.
Disruption of these rhythms, whether from exposure to light or from irregular sleep patterns, can raise blood pressure and heart rate, increase inflammation, and reduce heart-rate variability. Animal studies show that prolonged circadian disruption can trigger structural heart changes, such as hypertrophy and fibrosis, and can worsen heart failure.
Epidemiologic evidence connects these phenomena to shift work and other conditions that disturb these rhythms, thereby increasing the likelihood of cardiovascular mortality, coronary disease, and heart failure. Nighttime light exposure emerges as a key determinant of circadian disruption, and is therefore linked to higher rates of coronary disease and stroke, as well as to conditions like obesity, diabetes, and hypertension—each a known cardiovascular risk factor.
However, earlier studies that reported these findings often relied on satellite measurements of outdoor lighting or on small cohorts rather than direct data on personal light exposure. By using wrist-worn light sensors in about 89,000 UK Biobank participants, prior research had noted that brighter nights were associated with greater cardiometabolic mortality and type 2 diabetes; building on this, the current study asked whether individual daytime and nighttime light exposure could help predict or influence the incidence of cardiovascular disease over a follow-up of 9.5 years.
The Study Methodology
In the enrolled participants, light exposure was recorded continuously for one week via wrist-worn sensors, averaged into 24-hour profiles. Factor analysis identified two main exposure periods: daytime (7:30–20:30) and nighttime (00:30–6:00).
Participants were categorized into percentile groups based on light exposure, with the 0–50 percentile representing the darkest nights. Cardiovascular outcomes—including stroke, atrial fibrillation, heart failure, myocardial infarction, and coronary artery disease—were identified using hospital records, primary care data, and death registry data. Individuals with preexisting cardiovascular disease were excluded.
Using Cox proportional hazards models, the relationship between light exposure and disease risk was analyzed, sequentially adjusting for demographic factors (ethnicity, age, sex), socioeconomic variables (deprivation, education, income), and lifestyle factors (urbanization, diet, alcohol, smoking, and physical activity).
Additional models tested potential interactions with genetic risk scores, age, and sex. The primary results showed inverse associations for heart failure and stroke when physical activity was excluded from the full model. Compared with the darkest nighttime environment, participants with brighter nighttime exposure showed significantly higher risks of coronary artery disease, myocardial infarction, heart failure, atrial fibrillation, and stroke after adjusting for lifestyle, demographics, and socioeconomic factors.
Conversely, an increase in nighttime light exposure by one standard deviation was associated with an approximate 5–8% increase in the risk for all five cardiovascular outcomes. The associations were consistent across models and remained robust after adjustments, with sex and age—as noted earlier—acting as selective modifiers.
In Conclusion
There would be strong associations between greater nighttime light exposure and elevated cardiovascular risk, although the study could not establish causality.
Nonetheless, the authors note potential underlying vasculovascular and metabolic stress factors that could be driven by circadian disruption and sleep disturbance. With notable strengths—including a large sample, objective light measurements, and a long follow-up—the study’s limitations, such as possible residual confounding, limited ethnic diversity (mostly white participants), lack of information on the exact light sources, and the inability to prove causality, invite further investigation.
Nonetheless, the implications point to nighttime artificial lighting as a modifiable environmental risk factor for cardiovascular disease, underscoring the importance of maintaining dark nights and ensuring adequate daytime exposure to light in urban health strategies.
Source
Windred DP, Burns AC, Rutter MK et al. (2025). Light exposure at night and cardiovascular disease incidence. JAMA Network Open, 2025, 8(10): e2539031. DOI: 10.1001/jamanetworkopen.2025.39031.
Abbonati a Karla Miller
