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

Environ Health Prev Med · 2025 · Mixed · Low evidence

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MixedLow evidencePaper 2646

Study snapshot

PublicationEnviron Health Prev Med · 2025

Study typeanimal

Reported directionMixed

Evidence ratingLow

Abstract

Category: Toxicology Tags: 5G, millimeter wave, stress response, SAR, corticosterone, noradrenaline, rat study DOI: 10.1265/ehpm.24-00321 URL: pmc.ncbi.nlm.nih.gov Background Concerns have risen regarding the health effects of quasi-millimeter waves (qMMW) utilized in 5th-generation wireless communication systems. Guidelines have conservatively set a whole-body average specific absorption rate (WBA-SAR) of 4 W/kg—equivalent to a 1°C increase in core temperature—as the operational threshold for adverse effects. However, direct biological evidence for these thresholds has been lacking. Previous experiments showed a 1°C core temperature increase following 30 minutes of qMMW exposure at 4.6 W/kg in rats, highlighting the need for further investigation into biological stress responses near this threshold. Methods - Fifty-nine 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. - Experiments were conducted under normal (22.5°C, 45-55% humidity) and heat (32°C, 70% humidity) conditions, with rats restrained in acrylic holders. - Serum and urinary biomarkers of stress were repeatedly measured and analyzed using mixed models, accounting for sham exposure and between-subject variation. Key Findings - Sham exposure induced stress responses, primarily due to restraint stress. - After adjusting for sham effects, 28 GHz exposure elevated serum-free corticosterone 1 or 3 days post-exposure, especially in animals with >1°C rectal temperature change. - Urinary-free catecholamines indicated that 28 GHz exposure has an inhibitory effect on the stress response (notably noradrenaline) immediately after exposure. - Heat exposure amplified the effect, with a correlation between noradrenaline and tail surface temperature, supporting the role of noradrenaline in heat dissipation. Conclusions This study provides the first direct evidence that qMMW whole-body exposure near threshold values can modify the stress response in rats, as indicated by changes in corticosterone and noradrenaline. These findings offer biological insight into whole-body exposure thresholds specified by international safety guidelines and underscore the potential stress-related health risks associated with near-threshold 5G millimeter wave exposures.

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AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typeanimal

Effect directionmixed

PopulationYoung Sprague-Dawley rats (240–322 g)

Sample size59

ExposuremmWave · 28000 MHz · 40 minutes (single exposure)

Evidence strengthLowConfidence: 78% · Peer reviewed: yes

Main findings

In restrained rats, sham exposure induced stress responses. After adjusting for sham effects, 28 GHz whole-body exposure was associated with elevated serum-free corticosterone 1 or 3 days post-exposure, particularly in animals with >1°C rectal temperature change. Urinary catecholamines suggested an inhibitory effect on the immediate post-exposure stress response, notably noradrenaline, with heat conditions amplifying effects and noradrenaline correlating with tail surface temperature.

Outcomes measured

Serum-free corticosterone
Urinary-free catecholamines (including noradrenaline)
Rectal temperature change
Tail surface temperature

Limitations

Sham exposure itself induced stress responses due to restraint stress
Findings are from an animal model (rats), limiting direct generalization to humans
Effects depended on temperature change (>1°C rectal temperature change) and environmental heat conditions

View raw extracted JSON

{
  "study_type": "animal",
  "exposure": {
    "band": "mmWave",
    "source": "5G",
    "frequency_mhz": 28000,
    "sar_wkg": null,
    "duration": "40 minutes (single exposure)"
  },
  "population": "Young Sprague-Dawley rats (240–322 g)",
  "sample_size": 59,
  "outcomes": [
    "Serum-free corticosterone",
    "Urinary-free catecholamines (including noradrenaline)",
    "Rectal temperature change",
    "Tail surface temperature"
  ],
  "main_findings": "In restrained rats, sham exposure induced stress responses. After adjusting for sham effects, 28 GHz whole-body exposure was associated with elevated serum-free corticosterone 1 or 3 days post-exposure, particularly in animals with >1°C rectal temperature change. Urinary catecholamines suggested an inhibitory effect on the immediate post-exposure stress response, notably noradrenaline, with heat conditions amplifying effects and noradrenaline correlating with tail surface temperature.",
  "effect_direction": "mixed",
  "limitations": [
    "Sham exposure itself induced stress responses due to restraint stress",
    "Findings are from an animal model (rats), limiting direct generalization to humans",
    "Effects depended on temperature change (>1°C rectal temperature change) and environmental heat conditions"
  ],
  "evidence_strength": "low",
  "confidence": 0.78,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "5G",
    "millimeter wave",
    "qMMW",
    "28 GHz",
    "whole-body average SAR",
    "WBA-SAR",
    "restraint stress",
    "corticosterone",
    "catecholamines",
    "noradrenaline",
    "heat exposure",
    "rat"
  ],
  "suggested_hubs": [
    {
      "slug": "5g-policy",
      "weight": 0.78,
      "reason": "Study evaluates biological effects of near-threshold 5G (28 GHz) whole-body exposure relevant to safety thresholds/guidelines."
    },
    {
      "slug": "who-icnirp",
      "weight": 0.62,
      "reason": "Abstract explicitly discusses international safety guideline thresholds (WBA-SAR 4 W/kg) and provides biological evidence near those values."
    }
  ]
}

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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1265/ehpm.24-00321
PubMed: Not supplied

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