Dr Débora Constantino

Controlled studies have demonstrated that light supplementation benefits circadian entrainment, sleep and mood. Translating these findings into effective, real-world usage of light supplementation is, however, challenging because naturalistic and supplemental light exposure are shaped by personal habits and environmental light conditions. Bridging this translation gap is especially critical for older adults, given the reduced ocular light sensitivity associated with natural ageing, which exacerbates low daytime indoor light exposure in urban housing. We therefore set out to investigate the determinants of self-directed light supplementation in this population, and what the real-world feasibility and efficacy of daytime light supplementation is. We recruited 202 participants (63-92 years; 139 females) to our interventional, prospective, randomised study in three major EU cities at different latitudes (Amsterdam, Bologna, Tartu). Participants underwent a 2-week baseline assessment of light exposure, rest-activity patterns and sleep through wearables and daily diaries. Participants were then randomised to either 12 weeks of self-implemented indoor light supplementation using a lamp placed in their most frequently used room (> 8000 melanopic EDI, N = 98) or a no-intervention group. A subsequent 2-week reassessment showed that greater naturalistic light exposure was associated with increased daytime activity, consolidated wakefulness, better subjective sleep quality, and reduced metabolic disorder incidence. Individuals with lower naturalistic light exposure self-initiated earlier and longer indoor light supplementation across seasons, in which supplementation onset before 10:00 was associated with greater daytime activity and lower rest-activity fragmentation. These results confirm that this simple, non-pharmacological, and low-cost intervention has broad potential to support healthy ageing in urban settings.

The aim of the present study was to investigate the actigraphic sleep-wake and light exposure patterns of a 48-y-old healthy woman who travelled across one time zone (Italy to UK and vice versa) every two weeks for over 2.5 years (i.e. 852 night of sleep data, with 80% of recorded days retained for analysis after exclusion of travel and non-UK/Italy stays; 58% of time spent in Italy), and reported early evening somnolence and unpleasantly early wake-up time in the UK, especially immediately after travelling. She therefore started to wear an actigraph to monitor rest-activity and light exposure. Compared to Italy, UK-based recordings showed a significantly earlier midsleep (02:46 ± 01:00 vs. 03:02 ± 01:07 local clock time; p 

Low indoor light in urban housing can dis-rupt health and wellbeing, especially in older adultswho experience reduced light sensitivity and sleep/cir-cadian disruptions with natural aging. While controlledstudies suggest that enhancing indoor lighting mayalleviate the negative effects of reduced light sensitiv-ity, evidence for this to be effective in the real world islacking. This study investigates the effects of two lightconditions on actigraphic rest-activity rhythms and sub-jective sleep in healthy older adults (≥ 60 years) livingat home. Two photon-matched lights were compared; acontrol white light (4000 K) and a blue-enriched whitelight (17000 K) at two different intensities (300–450 lxand 1100–1200 lx respectively). Participants (n = 36, 25female) completed an 11-week randomized, cross-overstudy, comprising 1 week of baseline, 3 weeks of self-administered light exposure (2 h in the morning and 2 hin the evening), and 2 weeks of washout for each lightcondition. Participants completed sleep diaries, worea wrist actigraph and a light sensor necklace, and col-lected urine to measure 6-sulphatoxymelatonin. Longerduration of morning blue-enriched light significantlyimproved rest-activity rhythm stability and decreasedsleep fragmentation. More time spent above 2500 lxincreased actigraphy amplitude, daytime activity, andadvanced bedtime. Evening light exposure, however,increased sleep latency and lowered sleep efficiency.Our findings show morning blue-enriched light is ben-eficial whereas evening light should be avoided. Optimaltiming of self-administered light interventions thus mayoffer a promising strategy to improve sleep and rest-activity rhythms in older adults in real-world settings.