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This October, millions of Americans missed the opportunity to witness two spectacular celestial events: the northern lights and a rare comet. Light pollution, caused by the brightening of the night sky over North America, has been increasing by 10% annually since 2011, making it difficult for many to see such phenomena. However, the problem goes beyond stargazing. Growing research indicates that light pollution may be linked to various health conditions, including cancer, heart disease, diabetes, Alzheimer’s disease, and even low sperm quality.
The Impact of Light Pollution on Health
Scientists are increasingly concerned about how artificial lighting at night affects human health. Dr. John Hanifin, PhD, associate director of the Light Research Program at Thomas Jefferson University, explains that light pollution disrupts the natural contrast between day and night, confusing our physiological systems. “We’ve lost the contrast between light and dark, and we are confusing our physiology on a regular basis,” he says.
Light at night not only affects sleep but also contributes to health issues like high blood pressure, heart disease, strokes, and even cancer. A 2024 study involving over 13,000 people found that individuals living in areas with the brightest skies at night had a 31% higher risk of high blood pressure. A separate study from Hong Kong revealed a 29% higher risk of coronary heart disease in those living with greater light exposure, while another study linked nighttime light to a 17% higher risk of cerebrovascular diseases, such as strokes and brain aneurysms.
Circadian Rhythms and Disease Risk
Light pollution affects circadian rhythms, which regulate essential biological processes like hormone secretion and cell division. Dr. Christian Benedict, PhD, a sleep researcher at Uppsala University in Sweden, notes that nighttime light can disrupt this system, leading to problems like improper insulin release. This disruption may be one of the pathways to diabetes, as demonstrated by a study in China linking 9 million cases of diabetes to light pollution.
Research also shows that exposure to light at night suppresses melatonin production, a hormone critical for sleep and circadian rhythm regulation. Lower melatonin levels can increase cancer risk by reducing the body’s ability to fight cancer cells and raising estrogen levels, which can fuel breast cancer growth.
Alzheimer’s Disease and Light Pollution
Recent studies have shown that light pollution may even increase the risk of Alzheimer’s disease. A study published this fall found that outdoor light exposure at night was more strongly linked to Alzheimer’s than even alcohol misuse or obesity. Scientists believe that neuroinflammation, a marker of nervous tissue inflammation, plays a role, with melatonin suppression contributing to the disease’s progression.
What Can Be Done to Reduce the Impact?
While light pollution is a growing problem, there are steps individuals and communities can take to mitigate its effects. Simple measures like using blackout curtains, reorienting motion-detector lights, and planting trees can help reduce the amount of light entering homes at night. Organizations like the International Dark-Sky Association advocate for reducing outdoor illumination, supporting policies to preserve darkness.
Lastly, changing personal habits may also help. Dr. Hanifin suggests reading in bed with dim lighting instead of going for a late-night walk in light-polluted areas. By minimizing exposure to light at night, people can protect their health while potentially reclaiming the beauty of a dark, star-filled sky — and with it, the health benefits of natural darkness.
Sources:
- John Hanifin, PhD, Thomas Jefferson University
- Randy Nelson, PhD, West Virginia University
- Christian Benedict, PhD, Uppsala University, Sweden
