Prepubertal blue light exposure alters growth plate morphology and hormonal expression

The potential impact of increasing exposure to blue light (BL; 450-470 nm) from digital devices during early life on skeletal development remains largely unexplored. This study aimed to investigate the effects of BL exposure and its duration during the prepubertal period on the epiphyseal plate.

Thirty-six Sprague Dawley rats (18 male, 18 female), aged 21 days, were randomly divided into six groups: Control (CG), Blue Light-6 h (BL-6), and Blue Light-12 h (BL-12). CG rats were maintained under a standard 12-h light/dark cycle, while BL groups were exposed to blue light for 6 or 12 h daily until the first pubertal sign (vaginal opening or preputial separation). After euthanasia, femur and tibia lengths were measured. Epiphyseal plate and proliferation zone thickness were histologically assessed. IGF-1 and IGFBP-3 expression levels in the epiphyseal plate were evaluated using immunohistochemistry; serum levels were analyzed by ELISA.

Females: The median days for the onset of puberty were 38th, 32nd,and 30th for CG,BL-6,and BL-12 respectively(p = 0.001). The occipital tail length difference(%) was greater in BL-6 and BL-12 compared to CG(p = 0.029, p = 0.006). Femur length in BL-6 was greater than in CG(p = 0.04). No differences were found in serum IGF1 and IGFBP3 levels among the groups(p = 0.83, p = 0.61). The epiphyseal plate length, proliferation zone length, and IGF1,IGFBP3 expression in BL-12 were higher than in CG(p= 0.0004, p = 0.0004). Males: The median days for the onset of puberty were 38th, 30th,and 28th for CG,BL-6,and BL-12 respectively(p = 0.0001). The tail length difference (%) in BL-12 was greater than in CG(p = 0.02) while serum IGFBP3 levels in BL-6 were higher than in CG(p = 0.03). The epiphyseal plate length, proliferation zone length, and IGF1, IGFBP3 expression in BL-12 were higher than in CG(p = 0.0002, p = 0.0002). Degeneration and calcification consistent with changes in the proliferation zone were observed in both sexes.

Prepubertal blue light exposure induces structural and molecular changes in the growth plate, accelerating both proliferation and maturation. These changes mirror early gonadal maturation observed in previous studies and suggest systemic neuroendocrine involvement. While linear growth may initially increase, accelerated epiphyseal maturation could ultimately restrict final height.