Flores Villa, Lorna Minu; (2025) DAYLIGHT EXPOSURE: Assessment of its potential impact on sleep quality on people over 65 years old living in the UK. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Due to our social behaviours and lifestyle changes, people spend at least 80% of their time indoors, mostly under artificial light. In research and building design, daylight is considered a valuable asset because it is the primary source of free, good quality light and it is suggested that it has a positive influence on human performance, health and sleep quality. However, as people age, the quality of their sleep often declines, affecting at least 50% of the elderly population. Poor sleep among older adults is associated to a range of negative consequences, including increased fatigue, impaired cognitive function, mood disturbances, and a higher risk of falls. Sleep disruptions, particularly fragmented sleep and frequent awakenings at night, can lead to reduced alertness and cognitive performance, which in turn raises the likelihood of falls and injuries in the elderly. Additionally, inadequate sleep contributes to daytime drowsiness, further reducing mobility and reaction times, exacerbating the risk of accidents, and diminishing overall quality of life. Giventhat light plays a crucial role in circadian rhythm regulation, exposure to daylight (both indoors and outdoors) is expected to reduce sleep disruption. This study explores the relationship between exposure to daylight, seasonal variations, levels of physical activity, ability to go outside and sleep patterns in independently living older adults in London, UK. The study specifically focuses on winter and summer due to the pronounced differences in daylight duration between these seasons, which provide an opportunity to examine how variations in daylight availability influence sleep quality. A total of thirty-two participants, aged between 65 and 95 years, took part in this study. This age range was selected to provide a diverse sample of older adults, including individuals who remain relatively active as well as those who may face more pronounced sleep disturbances. The study utilised a mixed-methods approach, incorporating the Pittsburgh Sleep Quality Index (PSQI) questionnaire to assess sleep quality, the Morningness-Eveningness Questionnaire (MEQ) to determine chronotype, semi-structured interviews, and a seven-day sleep diary/log activity in which participants recorded their time spent outdoors. Data collection was conducted in both winter and summer to examine seasonal variations in daylight exposure and sleep patterns. It was expected that participants who reported less exposure to daylight during summer and winter would report worse sleep quality. However, the findings did not fully support this expectation. Despite substantial variations in daylight exposure between seasons, overall subjective sleep quality did not differ significantly between summer and winter in this cohort. Further analysis revealed an association between morning daylight exposure and the frequency of nighttime awakenings, suggesting that exposure to natural light earlier in the day may play a role in improving sleep consolidation. These findings challenge the assumption that increased daylight exposure associate with better sleep quality and highlight the need for further investigation into other contributing factors, such as indoor lighting conditions, individual health status, and daily routines, which may influence sleep in older adults.

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