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.
Animals ; Rats ; Rats, Sprague-Dawley ; Male ; Restraint, Physical ; Stress, Physiological/radiation effects* ; Corticosterone/blood* ; Biomarkers/blood* ; Microwaves/adverse effects*

BACKGROUND: Long screen time hours may be associated with behavioral problems in children. To better understand the relationship between children's behavioral problems and screen time, it the associated risk factors must be subdivided based on the purpose underlying screen use. This study examined the relationship between screen time based on intended usage and behavioral problems in Japan. METHODS: This study included 3,332 children aged between 7-17 years from the Hokkaido Study on Environment and Children's Health. From October 2020 to October 2021, the children and their parents answered questionnaires on the children's screen use duration (never used, <30 min, ≥30 min & <1 hour, ≥1 h & <2 h, ≥2 h) based on seven intended usage categories: watching television/video, video gaming, reading books/comics, sending/receiving e-mail/messages, browsing/posting on social networking services, studying for classes/homework, drawing/editing pictures/photos/videos, along with the Strengths and Difficulties Questionnaire (SDQ). Logistic regression was used to analyze the association between screen time, purpose of children's screen use, and behavioral problems across the 13 SDQ total scores. RESULTS: The mean ± standard deviation age of the participants was 12.4 ± 2.4-years-old, 487 (14.6%) children were determined to have behavioral problems, and the duration of screen time increased with their age. The children's primary purposes for screen use were watching television/video, video gaming, sending/receiving e-mail/messages, and browsing/posting on social networking services. Children who reported playing video games for ≥2 hours on weekdays had higher odds of problematic total difficulties scores than never user (Odds Ratio: 2.10, 95% confidence interval: 1.45-3.06). CONCLUSION Long video gaming screen time is associated with behavioral issues, hyperactivity/inattention, and prosocial behaviors in children. Conversely, watching television and videos for 30 min-1 h per day, using e-mail or messaging, and using social networking services were significantly association with reduced odds ratio for peer relationship problems as compared to children who never engaged in these activities. Longitudinal follow-up is needed to further examine screen time and problem behaviors.
Humans ; Screen Time ; Child ; Japan/epidemiology* ; Male ; Female ; Adolescent ; Problem Behavior/psychology* ; Surveys and Questionnaires ; Child Behavior ; Television/statistics & numerical data* ; Video Games/statistics & numerical data*