Blue Light-Blocking Glasses Attenuate Light-Induced Melatonin Suppression in Healthy Japanese Adults.

The human circadian pacemaker entrains to the environmental light-dark cycle and regulates daily sleep-wake patterns and various physiological functions. The circadian pacemaker receives light input from the retina via the retinohypothalamic tract, which contains intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing melanopsin. These ipRGCs are most sensitive to blue light (460-480 nm). Exposure to blue light before bedtime disrupts sleep and circadian rhythms, whereas blue light-blocking glasses have been shown to attenuate light-induced melatonin suppression. This study evaluated the effectiveness of commercially available blue light-blocking glasses (BG) in protecting nocturnal melatonin secretion under bright light conditions (~2,000 lux at eye level, 5,800K) in healthy Japanese adults. Seven participants (3 males, 4 females; age 22 ± 4 years) were exposed to 3 light conditions: dim light (< 5 lux, DL), bright light (~2,000 lux, BL), and bright light with blue light-blocking glasses (BL+BG). The BG block wavelengths shorter than 500 nm and reduce light intensity by 51%. Saliva samples were collected hourly from 20.0 h to 23.0 h and every 30 minutes from 23.5 h to 1.0 h in a controlled laboratory setting. Melatonin levels significantly decreased in the BL condition compared to the DL condition throughout the experiment. In contrast, melatonin levels in the BL+BG condition were not significantly different from those in the DL condition. These findings imply that blue light-blocking glasses attenuate light-induced melatonin suppression and help prevent phase-delay shifts of circadian rhythms. Further research is necessary to assess the broader effects of these glasses on sleep and circadian rhythms.