Light pollution makes 'time almost meaningless' — researcher

Night light disrupts antibody production rhythms, may raise risk of death, Israeli study finds

Tel Aviv University research on mice, with implications for humans, finds artificial lighting from sources as common as streetlights disrupts mammalian immune system’s natural sense of time

Artificial lighting from sources as common as streetlights may disrupt the circadian rhythms and immune systems of mammals, and even raise the risk of death, a new study by Tel Aviv University suggests.

Hagar Vardi-Naim, a doctoral student in life sciences, examined the effects of artificial lighting on the immune systems of two related species of small rodent — the golden spiny mouse and the common spiny mouse.

Both live in the Israeli desert and share the same geographical habitat. But while the golden spiny mouse is active during the day, the common spiny mouse operates at night.

The animals were transported from the Judean Desert to outdoor enclosures at Tel Aviv University’s Zoological Research Garden, where some were exposed to artificial light at night.

“Large parts of every mammal’s body, including our own, are regulated by an internal biological clock,” Vardi-Naim explained. “With a 24-hour rhythm based on the natural light-dark cycle, this biological clock signals to various organs and physiological systems, including the immune system, what they should do at different times of day.”

She continued, “For example, the levels of certain white blood cells rise and fall in the blood, and the body produces more or less antibodies at specific times. Such oscillations can enhance the immune response to bacteria or viruses, but for this, the body must know the time.”

She continued, “Light pollution alters the natural light-dark regime, disrupts the central clock’s synchronization with environmental time, and changes these patterns, rendering time almost meaningless.”

The spiny mice were kept in enclosures that simulated natural environmental conditions as far as possible. Half of the enclosures were illuminated at night with white LEDs, the most common type of lighting used today, at a relatively low intensity to simulate street lighting.

The control group was kept in natural light-dark conditions.

The researchers measured the percentage of white blood cells, called lymphocytes, in the rodents’ blood at several points during the 24-hour cycle.

They found a pattern similar to the human rhythm, with lymphocyte levels in the blood rising during rest hours, between 2 a.m. and 4 a.m.

They also discovered a clear 24-hour lymphocyte rhythm and found that the quantity of antibodies produced in response to an antigen (something that triggers an immune response) was time-dependent.

“We saw that animals exposed to an antigen during their rest hours produced far more antibodies than those exposed during their active hours,” said Vardi-Naim.

“Exposure to light pollution, however, completely muddled these rhythms,” she said. “Instead of a daily cycle of peaks and lows in the level of lymphocytes and immune response, we observed a complete flattening of the daily patterns. This means that the immune system loses its natural timing, and consequently, its response to infections, environmental stress, or vaccination might be less than optimal, possibly increasing the animals’ vulnerability over time.”

Furthermore, extensive and rapid mortality was observed among the mice exposed to light pollution, with a 2.35 times higher risk of death compared to the control group. Vardi-Naim noted that even though the exact cause of death could not be determined, the rise in mortality occurred alongside disruption of immune and endocrine, or hormonal, rhythms, suggesting a likely connection between damage to biological timing and reduced survival.

She added that while the spiny mice in the study were only an example, the findings had implications for all living creatures, including humans.

“Our results show that artificial lighting at night is not merely an aesthetic environmental change, but an active biological factor capable of disrupting critical physiological mechanisms. Chronic exposure to artificial lighting at night disrupted the timing of the mice’s immune and endocrine systems and impaired their survival under conditions that otherwise simulated the natural environment,” she went on.

“We believe that light pollution should be regarded as an environmental health risk with broad implications, not only for wildlife but also for human health and the ecosystem as a whole. Studies show that animals with weakened immune systems can transmit diseases to humans, and the human immune system may respond similarly. The study underlines the need to include biological considerations in lighting policies and to reexamine the scope and intensity of artificial lighting at night in both urban and open spaces.”

The study’s supervisors, both also associated with the university’s new Environmental School, were Prof. Yariv Wine, head of the Applied Immunology Laboratory at the School of Biomedicine and Cancer Research, and Prof. Noga Kronfeld-Schor, head of the Ecological and Evolutionary Physiology Laboratory at the School of Zoology, and rector of the university.

The research, published in Environmental Pollution, was supported by the Israel Science Foundation.