5G network deployment raises the issue of the health impact of these electromagnetic fields. Their effect on thermal regulation is of a “cold reesponse” type. In rats exposed to 900MHz, vasoconstriction was induced in the tail, with behavioral preference for warmer compartments. The hypothalamo-pituitary-thyroid axis is involved in thermogenesis: in response to cold, thyroid activity increases, stimulating heat production.

To assess thyroid activity after 5G exposure.

Ten 3-week-old male Wistar rats were randomized between 2 weeks’ 5G exposure at 3.5GHz and 1.5V/m (5G group; n=5) and no exposure (controls; n=5). After sacrifice, the thyroid gland was harvested for histomorphometry. Thyroid follicle and colloid areas were measured and the thyroid activation index (TAI: ratio of follicle to colloid area) was assessed.

Follicle and colloid areas were significantly greater in 5G (2729μm² vs 2444μm², P=0.0063; and 1317μm² vs 1015μm², P=0.0027 respectively) and TAI was significantly lower (5.62 vs 7.07, P <0.001). These results indicate thyroid hypoactivity.

There was a 5G effect, with histomorphometry demonstrating thyroid hypoactivity, suggesting mechanisms different from those underlying cold response. Impact of electromagnetic fields on thyroid function was previously reported, but results were heterogeneous and discordant depending on the type of exposure.

TSH and thyroid hormone assays are underway to reinforce assessment of thyroid function. Further studies are needed to explore the underlying mechanisms.