Illuminating the Risks of Nighttime Light for Cardiovascular Health
Year: 2025
Type: article
Abstract: In his treatise, Airs, Waters, and Places, 1 Hippocrates, the father of medicine, emphasized sunlightalongside other environmental factors such as temperature and the water supply-as a key determinant of population health, stating "when one comes into a city to which he is a stranger, he ought to consider its situation…for its influence is not the same whether it lies to the north or the south, to the rising or to the setting sun."While revealing some historical insight into how the timing of sunlight may impact human biology, Hippocrates was unable to assess the health impact of a more modern phenomenon that now is globally pervasive: exposure to artificial light at night (LAN).Satellite data show that exposure to LAN has increased by close to 50% from the period 1992 to 2017. 2 This is alarming because greater such exposure has been associated with an increased risk of a range of health conditions, including cardiometabolic disease and breast cancer.While such prior studies have often been large in scale, they have mostly been based on satellite-derived data on LAN, which may not yield insight into actual light exposure and other risk factors at the individual level.Meanwhile, accruing evidence has convincingly shown that sleep disruption, to which LAN can contribute, promotes cardiovascular disease (CVD), yet how LAN exposure at the individual level impacts the risk of CVD-the leading cause of premature death worldwide-remains unclear.This question has been addressed by Windred and colleagues 3 in a study examining the association of daytime and nighttime light exposure, and the prospective risk of 5 common CVDs, in a population of approximately 89 000 mostly middle-aged individuals.By tracking each individual's exposure for 1 week from 2013 to 2016-and subsequent disease risk for approximately 8 years-the new study found that those with greater exposure to LAN had an increased prospective risk of coronary heart disease, stroke, atrial fibrillation, myocardial infarction, and heart failure.3 For instance, the prospective risk of myocardial infarction was approximately 50% higher in those with the brightest compared with the darkest nights.In contrast, greater vs lower daytime light exposure was associated with a reduction in the prospective CVD risk.Importantly, the individual-level data also enabled the researchers to verify that the effects of LAN exposure were independent of several factors that may go hand in hand with mistimed light exposure.Indeed, the associations of LAN exposure with CVD risk remained significant even in models adjusting for the participants' preference in sleep timing (chronotype), actigraphy-based sleep duration, sleep efficiency, physical activity, and photoperiod.This indicates that LAN exposure risks were not secondary to, for example, curtailed sleep, or seasonal day length.While the work by Windred et al 3 provides unprecedented large-scale insight into how objective day-to-day LAN exposure is associated with future CVD risk, the work does not delve into the potential underlying mechanisms.Over hundreds of millions of years, evolution shaped our internal timing system-our circadian system-to anticipate daily light-dark cycles that approximate 24 hours (ie, circa diem), and which only change daily on the order of minutes, according to the shifting seasons.Today, however, irregular and recurrently shifting sleep-wake timing are both very common.Up to two-thirds of adults today shift their sleep-wake timing from weekdays to free days by 2 hours, in a phenomenon known as social jet lag (SJL), 4 and which is likely exacerbated by LAN.Both SJL and sleep irregularity have been shown to positively correlate with a more adverse cardiometabolic profile; higher SJL has been associated with higher blood triglyceride levels, insulin resistance, and adiposity.5 While Windred et al 3 tracked objective sleep duration, they did not examine sleep timing (such as SJL or sleep irregularity) and its association with light exposure.It therefore remains to be +
Source: JAMA Network Open
Author: Jonathan Cedernaes
Institution: Uppsala University
Language: English
Subfield: Global and Planetary Change
Field: Environmental Science
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,000
OpenAlex ID: W4415478472