Excessive exposure to artificial light at night, common in today’s tech-driven world, may negatively impact health. Studies show that higher bedroom light levels are linked to disrupted glucose metabolism, especially in people who eat late dinners. Prolonged exposure to bright lights can disturb circadian rhythms, affect sleep quality, and increase the risk of diabetes.
As technology advances rapidly, the night sky is no longer lit solely by the moon and stars. Instead, it's illuminated by a dazzling array of screens, neon lights, and electronic devices. From city streets to our bedroom windows, spaces that once thrived in quiet darkness are now bathed in artificial light. Urban areas are alive with neon signs, billboards, and street lamps, while at home, electric lights, TVs, computers, and smartphones have become night-time companions for many.
Previous research has shown that exposure to higher levels of artificial light at night is associated with a 13-22% increased risk of overweight and obesity. Increasing evidence now suggests that the risk of diabetes is also closely linked to nighttime light exposure, beyond just diet.
In order to delve deeper into this issue and understand the potential effects of artificial lighting on human health, a recent study published in Sci Rep focused on young university students. This research explored the relationship between bedroom nighttime lighting (LAN) exposure and glucose metabolism markers, also examining how meal timing, influenced by the body's circadian rhythm, played a crucial role in this phenomenon.
Participants and Methods
The study recruited 484 students aged 16-22 from two universities. After screening for diabetes, insulin resistance, or eating disorders, 256 participants' data were included in the analysis.
To measure bedroom LAN exposure, a portable light meter (model: TES-1339R) was used. Each participant was asked to place this device by their pillow for two consecutive nights to record the light intensity in their bedroom. These data were used to calculate the average light intensity (LANavg), and participants were classified into high or low exposure groups based on whether their LANavg exceeded 3 lux. The duration of exposure exceeding 3 lux (LAN3) was also measured, with 50 minutes serving as the dividing line for classification.
Sleep data was collected using a three-axis accelerometer (ActiGraph GT3X-BT), which participants wore on their non-dominant wrist for 7 days. The data were analyzed using ActiLife software to calculate various sleep parameters.
Meal timing information was self-reported by participants, who took photos of every meal they consumed for a week. Based on these records, researchers determined each participant’s average mealtime and classified them as "early" or "late" eaters. Specifically, those who had their first meal before 9 am and finished their last meal by 7 pm, or had at least 5 hours between their last meal and bedtime, were classified as "early." Others were classified as "late."
Additionally, fasting blood samples were collected to measure fasting glucose (GLU), triglycerides (TG), and fasting insulin (INS) levels. These were used to calculate the Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) and the Triglyceride Glucose Index (TyG), two markers of glucose handling ability.
Findings: Bright Bedroom Lights + Late Dinners = Higher Risk of Diabetes
The results revealed an average participant age of 18.7 years, with 32.8% male, and most participants were exposed to lower levels of LAN. When LANavg reached or exceeded 3 lux, or LAN3 exceeded 50 minutes, participants showed significantly higher glucose metabolism markers than those in the low exposure group. Even after adjusting for other influencing factors, there remained a near-linear relationship between LAN exposure and glucose metabolism markers (though the relationship between LANavg and TyG was non-linear).
Multivariable linear regression analysis showed that for each standard deviation increase in LANavg, INS, HOMA-IR, and TyG levels also rose. Similarly, each standard deviation increase in LAN3 produced similar results, with those in the high exposure group showing significantly higher metabolic marker levels than those in the low exposure group.
Figure 1: Distribution of glucose metabolism markers among groups with different night light (LAN) intensity and duration
Stratified analysis revealed that in people who ate dinner later, LAN exposure was significantly associated with increases in INS, HOMA-IR, and TyG. In contrast, this association weakened or disappeared among those who ate breakfast earlier.
Furthermore, gender-based analysis showed that in women, LAN exposure had a stronger association with glucose metabolism markers. However, when meal timing based on the circadian rhythm was considered, the difference between men and women became less pronounced. Sensitivity analysis confirmed that the primary results remained consistent, even after adjusting for relevant scale scores.
Figure 2: Multivariate linear regression of bedroom LAN exposure intensity and duration with glucose metabolism markers after stratification by different circadian rhythm-dependent meal time groups
This study highlights that nighttime lighting levels in the bedroom significantly influence young people's glucose metabolism, particularly for those who tend to eat dinner late. Prolonged exposure to bright nighttime lighting may disrupt the body's internal clock, suppress melatonin secretion, and interfere with the circadian rhythm system. These disruptions not only affect sleep quality but also reduce insulin sensitivity and impair blood sugar regulation, thereby increasing the risk of diabetes.
Light at Night = Higher Risk for Type 2 Diabetes
A previous study published in Lancet Reg Health Eur also examined the link between light exposure and health. The researchers analyzed data from 84,790 participants in the UK Biobank, with an average age of 62.3 years, 57.7% of whom were female.
The study found that compared to those in the darkest environments (with the lowest 0-50 percentiles of night light exposure), those exposed to brighter light at night had a significantly increased risk of developing type 2 diabetes. Specifically, participants in the 50-70, 70-90, and 90-100 percentiles of light exposure had adjusted hazard ratios (HR) of 1.29 [1.14-1.46], 1.39 [1.24-1.57], and 1.53 [1.32-1.77], respectively. This suggests that as light intensity at night increases, the risk of type 2 diabetes also rises.
Figure 3: Cumulative incidence of type 2 diabetes by night light exposure
Additionally, the study found that lower circadian amplitude (adjusted HR = 1.07-1.10) and either early or late circadian phase (adjusted HR = 1.06-1.26) were also associated with higher diabetes risk. This shows that not only the intensity of nighttime light exposure but also individual circadian patterns significantly influence diabetes risk.
Importantly, the study highlighted that both nighttime light exposure and genetic predisposition are independent predictors of type 2 diabetes risk. Even after considering genetic susceptibility, the risk of diabetes was still markedly higher among those exposed to bright light at night compared to those in darker environments.
Summary
When considering both studies, whether among vibrant young university students or older participants in the UK Biobank, the relationship between nighttime light exposure and metabolic health is undeniable. These studies show that bedroom lighting significantly impacts glucose metabolism in young adults, while for older participants, nighttime lighting exposure significantly increases the risk of type 2 diabetes. Both studies emphasize the critical role of circadian rhythms in this process.
These findings serve as a health alert, urging us to pay attention to the impact of nighttime lighting on people of all ages. Whether you're young or older, it's crucial to manage nighttime light exposure. This is especially important for individuals with high-risk factors, such as genetic susceptibility or poor lifestyle habits. Practical steps to mitigate exposure include reducing unnecessary screen time, using blackout curtains, and opting for low-brightness lighting at night to avoid potential health issues caused by excessive artificial light exposure.