Single exposure to near-threshold 5G millimeter wave modifies restraint stress responses in rats.

Akiko MATSUMOTO; Ikumi ENDO; Etsuko IJIMA; Akimasa HIRATA; Sachiko KODERA; Masayoshi ICHIBA; Mikiko TOKIYA; Takashi HIKAGE; Hiroshi MASUDA

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Single exposure to near-threshold 5G millimeter wave modifies restraint stress responses in rats.

Author: Akiko MATSUMOTO ¹ ; Ikumi ENDO ¹ ; Etsuko IJIMA ² ; Akimasa HIRATA ³ ; Sachiko KODERA ³ ; Masayoshi ICHIBA ¹ ; Mikiko TOKIYA ¹ ; Takashi HIKAGE ⁴ ; Hiroshi MASUDA ²
Author Information

1. Department of Social and Environmental Medicine, Saga University School of Medicine.
2. Department of Environmental Medicine, Kurume University School of Medicine.
3. Department of Electrical and Mechanical Engineering, Nagoya Institute of Technology.
4. Faculty of Information Science and Technology, Hokkaido University.
Publication Type:Journal Article
Keywords: 5G; Quasi-millimeter waves; Stress response biomarkers; Temperature; Whole-body exposure
MeSH: Animals; Rats; Rats, Sprague-Dawley; Male; Restraint, Physical; Stress, Physiological/radiation effects*; Corticosterone/blood*; Biomarkers/blood*; Microwaves/adverse effects*
From:Environmental Health and Preventive Medicine 2025;30():33-33
CountryJapan
Language:English
Abstract: BACKGROUND:In response to growing concerns about the health effects of quasi-millimeter waves (qMMW) used in 5th-generation wireless systems, conservative whole-body exposure thresholds based on indirect evidence have been proposed. The guidelines define a whole-body average specific absorption rate (WBA-SAR) of 4 W/kg which causes a 1 °C increase in core temperature, as the operational threshold for adverse health effects. To address the lack of direct evidence, we recently reported that a 30-minute exposure to qMMW at 4.6 W/kg resulted in a 1 °C increase in rat core temperature. Here, we further analyzed the near-threshold stress response for the first time, using biological samples from the aforementioned and additional experiments.
METHODS:A total of 59 young Sprague-Dawley rats (240-322 g) were exposed to 28 GHz for 40 minutes at WBA-SARs of 0, 3.7, and 7.2 W/kg, under normal (22.5 °C, 45-55% humidity), and heat (32 °C, 70% humidity) conditions. Rats were restrained in acrylic holders for dose control. We repeatedly measured serum and urinary biomarkers of stress response, aggregated the data, and analyzed them using a single statistical mixed model to subtract the effects of sham exposure and between-subject variation.
RESULTS:Sham exposure induced stress responses, suggesting an effect of restraint. After the subtraction of the sham exposure effect, 28 GHz appeared to induce stress responses as evidenced by elevated serum-free corticosterone 1 or 3 days after the exposure, which was more evident in animals with a change in rectal temperature exceeding 1 °C. Urinary-free catecholamines demonstrated an inhibitory property of 28 GHz frequency exposure on the stress response as evidenced by noradrenaline on the day of exposure. Heat exposure enhanced this effect, suggesting a possible role of noradrenaline in heat dissipation by promoting cutaneous blood flow, a notion supported by the correlation between noradrenaline levels and tail surface temperature, a critical organ for heat dissipation.
CONCLUSIONS:This study is the first to demonstrate that qMMW whole-body exposure can alter the stress response as indicated by corticosterone and noradrenaline at near-threshold levels. Our findings may provide insight into the biological basis of the whole-body exposure thresholds in the international guidelines.