Think about the number of streetlights, illuminated buildings, and neon lights in big cities around the globe. It’s probably safe to say that major cities are saturated with artificial light, which may be harmful to the health of their residents.
A recent study led by Ahnul Ha et al. (2024) suggests that exposure to nighttime outdoor artificial light may increase the risk of age-related macular degeneration (AMD), especially as we get older (1).
Good vision is about more than simply seeing the world around us, especially as we get older. We often associate being able to see with our independence, safety, and overall well-being.
Think about the things we do every day, things we normally take for granted. Cooking, fixing things around the house, getting ourselves around, paying bills, and staying mentally sharp and active. Then imagine your vision deteriorating so much that it becomes a struggle. Good eyesight is even more important than we realize.
What is age-related macular degeneration (AMD)?
The macula is a small, oval-shaped area about the size of a pinhead located in the center of the retina. This light-sensitive area is responsible for the sharp, detailed vision we need for activities like reading, driving, recognizing faces, and even perceiving color.
When the macula degenerates, so does our central vision. Whilst people suffering from macular degeneration can see things peripherally (off to the sides), they struggle to see what’s directly in front of them. This can happen in one eye or both.
As the name implies, the risk of age-related macular degeneration increases with age; it has become the most common cause of blindness in people over 60 (2).
There are two main types of macular degeneration: dry and wet. Whilst dry form is more common, it takes longer to develop and is harder to diagnose in the beginning, as symptoms are often minimal. The wet type affects fewer people but develops more rapidly; it can result in severe vision loss if not treated early.
Besides age, according to the American Optometric Association, the risk factors for developing age-related macular degeneration include genetics, UV-light exposure, smoking, poor nutrition, and lack of exercise.
The Effects of Outdoor Artificial Light at Night
It would be hard to imagine a city that’s not lit up at night. Besides allowing people to navigate safely, lighting has allowed cities to become vibrant hubs of activity when the sun goes down. And whilst we can’t imagine a city skyline without bright lights, there’s a growing concern that artificial light at night (ALAN) is not healthy for the human body.
The body has its 24-hour internal clock and circadian rhythm. This rhythm is tightly regulated and controls many essential physiological functions. The body’s temperature, when hormones are secreted, when we wake up or fall asleep, and even when genes get expressed are all influenced by this rhythm. Disturbing it can lead to serious health problems.
Link to certain cancers
As research on the relationship between ALAN and health continues to evolve, concerns have been raised about the possible link to certain cancers (such as breast and prostate), metabolic disorders (particularly conditions like obesity and diabetes), cardiovascular disease, rates of depression and chronic stress, and insomnia (to name a few) (3).
According to Ahnul Ha and his team (2024), there’s evidence to suggest that ALAN may have an impact on the health of the retina and optic nerve. They set out to study exposure to outside artificial light at night and “incident exudative AMD” (EAMD). This refers to the first time that someone is diagnosed with wet age-related macular degeneration (the type that develops quickly). (1)
The researchers used The Korean Health Insurance Service database along with the National Health Screening database to obtain medical records, demographic information, and insights into health behavior (such as smoking, alcohol consumption, and physical activity).
Their sample included individuals 50 years old or older diagnosed with EAMD between 2010 and 2011, allowing for a 10-year follow-up period to 2020. Included in the study was a control group with no diagnoses of EAMD until the study ended, but who had the same exposure assessment time as did the diagnosed group.
To measure and then calculate the amount of OALAN (outdoor artificial light at night) during the study, the researchers sourced the US Airforce Defense Meteorological Satellite Program Linescan System.
What did the study find?
After taking into account several individual and area-level risk factors, as one would probably expect, OALAN at the place where people lived was associated with a higher risk of EAMD.
Being older, being biologically male, living in an urban area, having a BMI (body mass index) greater than 25, smoking, consuming alcohol, and having high blood pressure or cholesterol are also associated with greater AOLAN and EAMD risk.
Speculation About the Development of EAMD
The researchers shared numerous possible reasons for the RPE (retinal pigment epithelium) cells to become impaired by OALAN. They’re a crucial layer of cells, located at the back of the human eye, that play an essential role in maintaining optimal vision and protecting the retina from light damage.
Excessive light exposure, particularly long-term blue light exposure, disrupts the mitochondria within the eye, reducing the viability of RPE cells by nearly 40%. The authors suggest that it is therefore likely that light pollution may cause the RPE cells to deteriorate significantly.
The authors also suggest that disruptions in the circadian rhythm, like those caused by ALAN (artificial light at night), can desynchronize the daily rhythm of phagocytosis in the eye. This is a process where waste and debris are removed in order to keep the eye healthy.
It’s believed that if this rhythm is disrupted, the process of waste removal may be incomplete, and cellular debris may accumulate. This could contribute to AMD and other vision problems.
The final point of speculation is the disruption of hormone secretions such as melatonin by ALAN. Disrupted circadian rhythms have been shown to inhibit the release of melatonin, resulting in a compromised immune system and systemic inflammation. Again, there is a strong link back to the RPE cells as well as to the development of EAMD.
What does this study tell us?
Whilst further studies are needed, the findings from this one suggest cause for concern when it comes to OALAN exposure and the increased risk of developing EAMD. If you live with the lights of the big city (or are exposed to blue light at home), limit your exposure where possible. It’s also a good idea to have regular eye exams and pay attention to symptoms like blurry or fuzzy central vision, distorted lines or objects, central blind spots, or difficulty reading. Get these issues checked out sooner rather than later to protect the health of your eyes.
- Kim SH, Kim YK, Shin YI, et al. Nighttime Outdoor Artificial Light and Risk of Age-Related Macular Degeneration. JAMA Netw Open. 2024;7(1):e2351650. doi:10.1001/jamanetworkopen.2023.51650
- Yuye Wang, Yifan Zhong, Liang Zhang, Qijun Wu, Yihchung Tham, Tyler Hyungtaek Rim, David Mutugi Kithinji, Jingyang Wu, Chingyu Cheng, Huiying Liang, Honghua Yu, Xiaohong Yang, Lei Liu; Global Incidence, Progression, and Risk Factors of Age-Related Macular Degeneration and Projection of Disease Statistics in 30 Years: A Modeling Study. Gerontology 5 July 2022; 68 (7): 721–735. https://doi.org/10.1159/000518822
- Liu, Y.; Yu, C.; Wang, K.; Kwan, M.-P.; Tse, L.A. Linking Artificial Light at Night with Human Health via a Multi-Component Framework: A Systematic Evidence Map. Environments 2023, 10, 39. https://doi.org/10.3390/environments10030039
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