How Light at Night Affects Brain, Mood, and Metabolism

Neuroscientist Dr. Randy J. Nelson warns that exposure to artificial light at night can disturb circadian rhythms, harming brain function, metabolism, mood, and immune health. As chair of the Department of Neuroscience at West Virginia University, Nelson has spent over a decade studying how even low levels of nighttime light exposure—such as from streetlights, bedside lamps, or electronic screens—can trigger physiological changes far beyond poor sleep.

How Light at Night Disrupts the Body

Nelson’s research shows that artificial light at night interferes with the body’s internal clock, suppressing melatonin production and disrupting the natural light–dark cycle that governs many biological functions. This disruption affects multiple systems:

Brain and mood: Exposure to dim light during normal sleep hours has been shown in animal studies to increase brain inflammation, reduce levels of brain-derived neurotrophic factor (BDNF), and cause behaviors linked to depression.

Metabolism: Nighttime light alters circadian gene expression, which can impair insulin sensitivity, promote weight gain, and disturb glucose regulation.

Immune function: Irregular light exposure can suppress normal immune responses or cause chronic low-grade inflammation, increasing vulnerability to illness.

These effects can appear even with relatively low light levels—around 5 lux, similar to the glow from a dim bedside lamp. Research has linked such exposure to a greater risk of metabolic disorders, cardiovascular disease, and mood disorders.

From Laboratory Studies to Clinical Trials

While much of the foundational work comes from controlled lab experiments, Nelson’s team is translating these findings into real-world applications through clinical trials. In hospital intensive care units (ICUs), patients are often exposed to bright artificial light around the clock, which may slow recovery. Nelson’s group is testing interventions such as adjusting light wavelengths and timing to improve outcomes for stroke and cardiac surgery patients.

Another study focuses on night-shift nurses, who are at high risk for sleep problems and mood disturbances. By using blue-light visors at specific times, the research aims to help reset their circadian rhythms, potentially improving cognitive performance and overall well-being. These trials explore whether similar strategies could support shift workers in other industries, where irregular schedules make it hard to maintain natural sleep–wake cycles.

Nelson also points out that the time of day can affect research results. Experiments done in the morning might give different outcomes than those done in the evening, but many studies don’t record or control for this. Keeping track of when tests are done could make biomedical research more consistent and reliable.

Practical Steps for Protecting Circadian Health

Nelson’s work underscores that small lifestyle changes can help protect circadian rhythms and reduce the health risks of artificial light at night. Strategies supported by current evidence include:

Limit blue light exposure after sunset: Use warmer-toned light bulbs in the evening and enable night mode on screens.

Block ambient nighttime light: Blackout curtains or eye masks can reduce intrusion from streetlights and outdoor lighting.

Maintain regular sleep–wake cycles: Going to bed and waking up at consistent times helps reinforce natural rhythms.

Increase daylight exposure: Spending at least 30 minutes outside in the morning boosts alertness and helps anchor the circadian clock.

Nelson’s recent book, Dark Matters, offers a detailed guide for the public on aligning daily habits with biological timing to improve long-term health.

Artificial light at night is now recognized as a growing public health concern, with research linking it to chronic disease risk and mental health challenges. Nelson’s investigations—from molecular changes in the brain to patient care in the ICU—show that circadian disruption is not just a sleep issue but a multi-system health problem. Adopting circadian-friendly lighting practices and reducing nighttime light exposure could play a key role in preventing illness and improving well-being.

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