Avoid fearing the dark.

Even low levels of artificial light at night (ALAN), comparable to typical street lamps, interfere with the immune cycles of wild rodents, resulting in a 2.35 times higher death rate, reveals a pioneering study from Tel Aviv University.

Conducted at TAU's Zoological Garden (the I. Meier Segals Garden for Zoological Research), the experiment involved two native mammal species: the golden spiny mouse (Acomys russatus) and the common spiny mouse (Acomys dimidiatus). While ALAN's impact on circadian rhythms is established, its effects on immunity remained underexplored. This marks the world's first proof of ALAN weakening mammalian immunity.

Recently, Ben-Gurion University researchers in Beersheba, led by Yael Lehnardt, demonstrated noise pollution altering animal behaviors, particularly in birds. Artificial night lighting now joins the list of cautioned environmental threats.

Doctoral candidate Hagar Vardi-Naim from the George Wise Faculty of Life Sciences led the ALAN study, guided by Prof. Yariv Wine, head of the Applied Immunology Laboratory at the Shmunis School of Biomedicine and Cancer Research, and Prof. Noga Kronfeld-Schor, director of the Ecological and Evolutionary Physiology Laboratory at the School of Zoology.

The alarming results appear in the journal Environmental Pollution, titled "Artificial light at night disrupts immune rhythms in wild rodents under semi-natural conditions."

Kronfeld-Schor, TAU's rector for the School for Environment and Sustainability and former zoology department chair, explained to The Jerusalem Post that ALAN is simpler to mitigate than other pollutants - if cities and public facilities dim lights after dark.

She recommends total darkness for sleep among humans and animals alike, sans night lights, noting, "Non-moonlight illumination impairs immunity. Children sleep fine in the dark."

The team assessed ALAN's toll on the immune systems of these desert-dwelling mice, relocated from the Judean Desert to TAU's outdoor enclosures. Some faced ALAN exposure. The golden spiny mouse is diurnal, while its common cousin is nocturnal, despite shared habitats.

"Every mouse under ALAN perished," Kronfeld-Schor reported. Pathology revealed immune collapse. "This applies to all mammals." Immune defenses form a layered shield against pathogens and maintain tissue health.

She advises avoiding phones and screens - especially blue-light emitters - pre-bedtime; use night mode if needed. Opt for yellow lights and lower intensities in public spaces.

"We consulted Jerusalem Biblical Zoo on Givat Masua expansion to shield animals. Efforts to dim Western Wall lights failed due to security or aesthetic preferences. Light pollution pervades Israel, even stargazing haven Mitzpe Ramon."

"No ALAN laws exist in Israel, and enforcement would prove challenging," Kronfeld-Schor added. "Colleagues in the US and Europe praised our work."

'Controlled by internal biological clocks': Vardi-Naim

Vardi-Naim noted, "Mammalian bodies, including humans, rely on a 24-hour internal clock synced to natural light-dark cycles, directing organs like the immune system."

"Lymphocyte levels fluctuate daily; antibody production peaks at set times, optimizing defenses. But light pollution desynchronizes this, erasing temporal cues."

Mice inhabited near-natural enclosures; half received white LED night illumination mimicking street lights, others only natural cycles of sun, moon, and stars.

Blood tests across 24 hours mirrored human lymphocyte patterns, peaking 2-4 a.m. during rest.

A robust daily rhythm emerged, with antibody responses to antigens strongest during rest phases.

"Rest-hour antigen exposure yielded far more antibodies than active periods," Vardi-Naim said.

ALAN obliterated these cycles, flattening lymphocyte and response patterns. "The immune system loses timing, weakening infection, stress, or vaccine reactions, heightening vulnerability."

ALAN-exposed mice faced 2.35-fold mortality risk. Though exact deaths unclear, immune-hormonal disruptions suggest causation.

"These mice exemplify broader impacts on all creatures, humans included, and ecosystems," Vardi-Naim stressed.

"ALAN actively disrupts physiology, not just aesthetics. It impaired survival in simulated wild settings by scrambling immune-endocrine timing."

"Treat light pollution as a health hazard affecting wildlife, humans, and ecology. Weakened animals may spread diseases; human parallels likely. Integrate biology into lighting rules for cities and wild areas."

Using wild models in realistic conditions underscores real-world immune insights over lab sterility.