Correction to: Perinatal mental health issues in consultations regarding medication use during breastfeeding: Insights from the Japan Drug Information Institute in Pregnancy (JDIIP).

Parkinson's disease (PD) is a neurodegenerative disorder characterised by the coexistence of motor and non-motor symptoms. Among the non-motor manifestations, sleep disturbances are highly prevalent, affecting up to 90% of individuals with PD, and significantly reducing quality of life and daytime functioning. Sleep impairment may refer to diurnal or nocturnal symptoms including sleep fragmentation, difficulties with sleep initiation, but also excessive daytime sleepiness (EDS). The underlying biology of sleep disorders in PD is heterogenous. Despite this heterogeneity, it is likely that neurodegenerative changes within central sleep regulatory areas, particularly the hypothalamus, play a crucial role in the pathophysiology of sleep and circadian rhythm disruptions observed in PD. The suprachiasmatic nuclei (SCN), located in the anterior hypothalamus, serve as the central circadian pacemaker, regulating endogenous physiological cycles with an approximate 24-h period. These are likely perturbed in PD. The circadian cycles are synchronised to the environmental light or dark and to social activity cycles by zeitgebers (cues indicating environmental time). Light represents the most effective zeitgeber of the circadian system. Supplementary exposure to light has been shown to have beneficial effects on sleep quality and daytime vigilance in healthy older people and patients with dementia. Stimulated by these findings, bright light therapy (BLT), utilising the whole spectrum of visible (white) light, was introduced as a measure to improve circadian rhythmicity, mood and sleep disorders in PD. BLT is considered a safe non-pharmacological treatment option, with only minor side effects. The therapeutic effects are attributed to its role as a zeitgeber, helping to reset circadian rhythms. This resetting is reflected by shifts in serum melatonin concentrations, which play a crucial role in regulating sleep-wake cycles. BLT has been investigated as a non-pharmacological intervention for managing non-motor symptoms in PD. Exposure to light intensities ranging from 1000–6000 Lux for durations of 30 to 90 min, administered either in the morning or evening, has been shown in some studies to improve mood, sleep quality and motor function in individuals with PD. Nonetheless, the efficacy of BLT as treatment in PD has yielded conflicting results. Traditional methods of delivering this therapy, i.e., light boxes, can be impractical for some patients, potentially affecting adherence and overall effectiveness. Moreover, as already alluded to, BLT encompasses the whole spectrum of visible light and, as such, often requires higher light intensities to achieve therapeutic effect. Emerging evidence suggests that targeting specific wavelengths, particularly in the blue spectrum (approximately 460–480 nm) may offer a more efficient approach in entraining the SCN compared to monochromatic light with a wavelength around 555 nm. Moreover, blue light around 460 nm wavelength was more effective in phase-shifting circadian output and necessitated a shorter duration and lower irradiance to achieve this effect compared to exposure to white light.