Efectividad de la exposición a luz incidente en la atenuación de la cronodisrupción en el envejecimiento

Abstract

In recent decades, Western countries have seen higher life expectancy thanks to biomedical advances and social and health care, which increase longevity and improves quality of life. Aging, however, can lead to a decline in neurophysiological functions and morphological, neurochemical and functional alterations of the circadian system (SC), leading to chronodisruption (CD), i.e. an alteration in the adjustment, synchronization and consolidation of circadian rhythms. Light and light-dark contrast is one of the main zeitgebers in the adjustment of circadian rhythms. It is common for institutionalised elderly people to have less exposure to natural and often artificial light due to the institutions' own architecture, which, together with eye problems and difficulty in mobility, are the factors responsible for CD. The main objective of this doctoral thesis has been to evaluate the effectiveness of natural incident light and bright artificial light exposure in attenuating chronodisruption in institutionalized elderly people. The thesis comprises four experimental studies, two pilot studies and two larger, more comprehensive studies to reinforce the data provided by the former. Study 1 assesses the overall cognitive state and emotional state before and after the application of bright light therapy (TLB), resulting in a significant improvement in both parameters. Study 2 evaluates changes in circadian parameters and melatonin levels from the records of resting activity and peripheral temperature (TP) after application of TLB. The results show a significant improvement in most circadian parameters. Study 3 compares the circadian parameters and sleep quality of a sample of elderly people institutionalized in homes with different architectures and exposure to different natural incident light. The results provide a positive correlation between light incidence and light-dark contrast, with a robust sleep-wake rhythm and improved sleep quality. Finally, study 4 demonstrated the effectiveness of TLB on improving circadian, cognitive, functional, clinica and health variables of institutionalized elderly people. All four studies have provided information on the effectiveness of natural light and TLB in those parameters and variables responsible for the adjustment of circadian rhythms and therefore in the attenuation of CD. The studies were carried out under natural conditions and with a non-invasive outpatient methodology. From the results of the present work it can be concluded that a greater exposure of natural or artificial light in the early morning hours and a respected light-dark contrast during the day-night period, allow for greater stability and improvement in the adjustment, synchronization and consolidation of sleep-wake rhythm; cognitive, functional, health and quality of life variables and an improvement in the quality of sleep, therefore, attenuation of CD.