Don’t be afraid of the dark.
Even minimal artificial light at night (ALAN) – at intensities equivalent to standard street lighting – disrupts the natural immune rhythms of wild rodents, leading to a 2.35-fold increase in mortality, according to a first-ever study at Tel Aviv University.
The study was conducted at TAU’s Zoological Garden (the I. Meier Segals Garden for Zoological Research) on two species of local mammals – the golden spiny mouse (Acomys russatus) and the common spiny mouse (Acomys dimidiatus). While the disruptive effect of artificial light on circadian rhythms is well documented, little research on the effects on immune function has been conducted until now. Their research is the first in the world to prove the connection between ALAN and weakened immunity in mammals.
Just last month, researchers at Beersheba’s Ben-Gurion University of the Negev, headed by Yael Lehnardt, published a study showing that the impact of noise on the natural world disrupts the behavior of animals, especially birds. Now, artificial lighting at night has been cautioned against as well.
The ALAN study was carried out by doctoral student Hagar Vardi-Naim at the George Wise Faculty of Life Sciences. It was supervised by Prof. Yariv Wine, head of the Applied Immunology Laboratory at the Shmunis School of Biomedicine and Cancer Research, and Prof. Noga Kronfeld-Schor, who heads the Ecological and Evolutionary Physiology Laboratory at the School of Zoology.
The disturbing findings were published in the journal Environmental Pollution under the title “Artificial light at night disrupts immune rhythms in wild rodents under semi-natural conditions.”
Kronfeld-Schor, who is rector of TAU’s School for Environment and Sustainability and a former chairman of the zoology department, told The Jerusalem Post in an interview that, compared to other types of pollution, ALAN is relatively easier to deal with – if municipalities and various public buildings agree to turn down the lights at night.
She urged that not only non-human animals but also children and adults go to sleep at night in darkness, without a night light, as “illumination that is not moonlight weakens the immune system. Children are not afraid to go to sleep in the dark,” she insisted.
The researchers examined the effects of artificial lighting on the immune systems of the two related species of mice. The animals were taken from the Judean Desert to outdoor enclosures at TAU’s Zoological Garden, where some of them were exposed to ALAN. Both live in the Israeli desert, sharing the same geographical habitat, but they differ in the time that they’re active. While the golden spiny mouse is energetic during the day, the common spiny mouse is frisky at night.
“All the mice that were exposed to ALAN died,” said Kronfeld-Schor. “We conducted pathology exams and found that their immune systems had stopped working to protect the body. What we found is relevant to all mammals.” These immune systems are meant to act as a complex, multi-layered defense network that protects the body from viruses, bacteria, parasites, and foreign substances, while ensuring a constant state of functional integrity in the tissues.
She urged staying away from cellular phones and other screens, especially those producing blue light, before going to bed; if necessary, they can be put in night mode. Municipalities and public institutions can switch to yellow light and reduce the level of illumination.
“We were called in by the Jerusalem Biblical Zoo, where the Givat Masua neighborhood is being expanded, to advise how to protect the animals. We tried to reduce the light at the Western Wall at night, but the authorities there opposed this, they claimed, for security reasons or because people liked it that way. There is light contamination everywhere in Israel, even at Mitzpe Ramon in the Negev, which is recognized as a destination for stargazing and astro-tourism.”
Israel hasn't passed any legislation on limits for ALAN, but even if there were laws, they would be difficult to enforce,” continued Kronfeld-Schor. “Our study brought us many positive reactions from colleagues in the US and Europe.”
'Regulated by an internal biological clock': Vardi-Naim
Vardi-Naim explained that “large parts of every mammal’s body, including our own, are regulated by an internal biological clock. 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.
“For example, the levels of certain white blood cells (lymphocytes) rise and fall in the blood, and the body produces more or fewer antibodies at specific times. Such oscillations can enhance the immune response to bacteria or viruses, but for this, the body has to know the time. Light pollution changes the natural light-dark regime, disrupts the central clock’s synchronization with environmental time, and changes these patterns, rendering time almost meaningless.”
They kept the spiny mice in enclosures that simulated a natural environment as much as possible, said Vardi-Naim. Half of the enclosures were illuminated at night with white LED, the most common type of lighting used today, at a relatively low intensity that simulates street lighting, while the control group was exposed only to natural light-dark conditions – the sun, moon, and stars.
The researchers measured the percentage of lymphocytes in the mice’s blood at several points in the 24-hour cycle and found a pattern similar to the human rhythm, with the levels in the blood rising during rest hours – between two and four in the morning.
In addition, they discovered a very clear 24-hour lymphocyte rhythm. They found that the number of antibodies produced in response to an antigen (a substance that evokes the immune system’s response, such as a virus or vaccine) is 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,” Vardi-Naim continued.
“Exposure to light pollution, however, completely muddled these rhythms. 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.”
In addition, 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. The researchers note that even though the exact cause of death could not be determined, the rise in mortality occurred alongside disruption of immune and hormonal rhythms, thus suggesting a likely connection between damage to biological timing and reduced survival.
Vardi-Naim emphasized that the spiny mice in the study are only one example and that the findings have implications for all living creatures, including humans and the whole ecosystem.
“Our results show that ALAN is not merely an aesthetic environmental change, but an active biological factor capable of disrupting critical physiological mechanisms. Chronic exposure to ALAN disrupted the timing of the mice’s immune and endocrine systems and impaired their survival under conditions that otherwise simulated the natural environment.
“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 it is possible that the human immune system responds in a similar way. The study underlines the need to include biological considerations in lighting policies and to reexamine ALAN scope and intensity in both urban and open spaces.”
The team stressed that by studying animals that live in conditions close to their natural environment rather than in sterile laboratory settings, their research highlights the value of using wild models to understand how the immune system functions in the real world.
