TRAJECTORY MODELS IN COGNITIVELY HEALTHY ELDERS

The old-age population is increasing at a considerably faster rate than the worlds total population. According to the United Nation report (2017), currently Europe has the highest proportion of elderly people of all the continents, but it is remarkable that in 2050 there will be an increase in the number of people over 60 also in China, in some nations of Africa and in Latin America. However, the increase in elderly people is notable because aging brings important changes in health status: cognitive and physical functioning, together with the degree of disability, are important indicators used to try to quantify the quality of health, in the later stages of life. Moreover aging is also frequently related to non-communicable diseases. Among brain disorders and non-communicable diseases, dementia, which is an umbrella term for several diseases, is the major cause of disability among older adults having major consequences on cognitive impairment and on mortality. The general aim of this thesis was to study in depth the health status using trajectory models of cognitive function, physical activity, and disability in a cohort of elderly people. Its specific aims were to identify trajectory and multi-trajectory trends of cognitive, physical functioning and disability on non-demented elderly people living in the North of Italy in order to profile each multi-trajectory group identified. Besides another aim was to describe trajectories of cognitive decline for a part of the older adults of the Italian population-based cohort and for the Swedish population-based cohort. This PhD thesis is based on data gathered from the two population-based studies: the Italian InveCe.Ab (Invecchiamento Cerebrale in Abbiategrasso, i.e., Brain aging in Abbiategrasso) study conducted by the Golgi-Cenci Foundation, Abbiategrasso (Milan) and the Swedish database of SNAC-K study (Swedish National Study on Aging and Care-Kungsholmen) carried out by the Stockholm Gerontology Research Center in collaboration with Aging Research Center (ARC), Karolinska Institutet. To achieve the aims, three outcomes were used in the present work. Cognitive function was assessed using the Mini Mental State of Examination (MMSE) scale administered at every follow-up time in both studies.The physical status was assessed using the walking test as gait speed. To test the preservation from disability during all the follow-up times the Activity Daily Living scale was administered (ADL). This scale takes into account difficulty in daily living activities, such as bathing, using the toilet, dressing, feeding and moving from one room to another. To describe different courses of the three outcomes, the statistical methodology of Group-Based Trajectory Model (GBTM) was applied. This method uses the trajectory groups as a statistical device to find the unknown distribution of trajectories across subjects. The groups identified by using the GBTM were profiled and compared using a multinomial logistic regression model. The results described by the multi-trajectories are good for most of the elderly: they have quite stable cognitive, physical function and they are free from disability in daily activities. Aging is a real, concrete and complex issue for human beings. Constancy, perseverance and well planned research are the keys to deepen in order to have a better knowledge of this phenomenon and its lifespan.