Promoting the health of older people to better support them remains one of the major challenges of the 21st century. More and more experts in gerontology (doctors, psychologists, sociologists, ...) are now advocating a holistic approach to older people. The recent recommendations of the WHO (2016) also invite us to favor an approach to aging centered on the potentialities and resources of older people more than on their deficiencies and diseases. Thus, taking into account the older person in his or her entirety ("body and mind") is a must for aging well and preventing the loss of functional independence. However, the relationship between physical and mental health remains poorly understood.
The psychosomatic model postulates that well-being and positive affects have an impact on physical health. It has thus been shown that good psychological health (e.g., positive mood, hope, optimism) has long-term beneficial effects on longevity, cardiovascular health, and chronic diseases. Conversely, poor mental health (e.g., presence of depressive symptoms) affects the health of older subjects and increases mortality risk. These results are in line with the so-called top-down approaches which postulate that well-being is a psychological trait that is the cause of future personal evaluations. In this psychosomatic approach, well-being, positive affect (i.e., good psychological health), is seen as antecedent to physical health. Naturally, it would seem unlikely that well-being would predict improved health for older people. However, well-being or the presence of positive affect could well predict different trajectories of "health" in ill older people.
In contrast, the so-called disability model postulates that physical health problems have an impact on psychological health, including well-being. This bottom-up approach considers physical health problems as antecedents of well-being. A study conducted by members of the laboratory supporting this project argues for this approach. The results show that poor physical health would unidirectionally predict poor life satisfaction over the long term.However, no study to date has been able to confirm the prevalence of one model over the other.
The main hypothesis of this research is based on the presence of a bi-directional pattern between physical and psychological health, and thus on the absence of a unique prevalence of one pattern over the other for the entire target elderly population. The investigators also hypothesize that the causal links between physical and psychological health may vary over time as a function of specific mediators, including inflammatory and metabolomic profiles. Our second hypothesis thus postulates that biological profiles could mediate the bi-directional links between physical and psychological health. For example, the investigators know that negative psychological affects have a negative impact on our "physical" health, so the investigators can assume that positive psychological affects can produce an anti-inflammatory effect, thus allowing us to be in better physical health (protective factor).
