Poor Diet and Lack of Exercise Correlate with Risk of Cognitive Decline and Dementia
It is not surprising to find data showing that a poor diet and lack of exercise correlated with an increased risk of later neurodegeneration and dementia. Plenty of studies exist to note that correlation. The question is the degree to which it is correlation versus causation. There are good reasons to believe that regular exercise slows the onset of neurodegeneration, quite clear mechanistic links that are demonstrated to be causal in animal studies. Equally, a poor diet and lack of exercise correlate with many other potential contributing factors in human populations, not least of which is frailty and other manifestations of aging. So to what degree do these correlations in human data reflect protective effects versus the tendency of those who are most affected by aging, and therefore most likely to decline more rapidly, to eat poorly and exercise little?
New research has found that both diet and exercise can influence the risk of cognitive decline (CD) and dementia by potentially influencing hippocampal neurogenesis long before their onset. The investigation studied how the blood of participants with and without CD and dementia could influence hippocampal neurogenesis in laboratory settings and whether diet and exercise were important factors. Specifically, blood samples of 418 French adults over the age of 65 were collected 12-years prior to CD and dementia diagnosis and tested on human hippocampal stem cells. Additionally, information on each participant's sociodemographic, lifestyle, and clinical data were collected and incidence cognition status and dementia were measured every 2 to 3 years over a 12-year period.
Over the course of the study, the researchers established that 12 years prior to diagnosis, both CD and Alzheimer's were associated with levels of neural stem cell death. The team also found that exercise, nutrition, vitamin D levels, carotenoid and lipid levels are all associated with the rate at which cells die off. Furthermore, physical activity and nutrition were key factors that then also determined CD status. Specifically, researchers found that reduced physical activity and increased malnutrition both increased cell death which in turn increased the risk for future CD.
While previous studies have established that diet and exercise have some protective effects against CD and dementia, these roles have been poorly understood at the neurobiological level. To date, studies on animals have shown how diet and exercise can directly influence hippocampal neurogenesis, potentially explaining how exercise and diet may biologically exert their effects, but this study sheds further light on this in the context of a human model. "If an individual displays an increase in their levels of cell death during differentiation (when neural stem cells are becoming neurons), we can look at this as a potential warning sign of CD. Conversely, a decrease in levels of cell death during proliferation (the process by which a single cell divides into a pair) and reduced hippocampal progenitor cell integrity could be viewed as a predictor for Alzheimer's disease and vascular dementia, respectively."