Examination of potentially modifiable dementia risk factors across the adult life course: The Framingham Heart Study

Cognitive reserve over the life course and risk of dementia: a systematic review and meta-analysis

Background

The number of people with dementia is soaring. Cognitive reserve has been thought to be associated with dementia risk. It is not clear at which period in the life course and which cognitive reserve proxies contribute to the reduced risk of dementia.

Methods

By scanning four databases (PubMed, Embase, Web of Science, and MEDLINE) up to Jun 3, 2023, longitudinal studies of life-course cognitive reserve and risk of dementia were found. The HRs and 95% CIs for each study were summarized using random effects models. Subgroup analyses and sensitivity analyses were conducted. Utilizing funnel plots, Begg and Egger tests, publication bias was investigated.

Results

A total of 27 studies were included, containing 10 in early-life, 10 in middle-life, and 13 in late-life. All studies used validated questionnaires to measure cognitive reserve, and dementia diagnosis followed recognized worldwide guidelines. All included studies were of medium or low risk. Cognitive reserve in early-life (Hazard ratio (HR): 0.82; 95% confidence interval (CI): 0.79-0.86), middle-life (HR: 0.91; 95% CI: 0.84-0.98) and late-life (HR: 0.81; 95% CI: 0.75-0.88) all have protective effects on dementia risk. Multiple sensitivity analyses showed consistent results.

Conclusion

Dementia risk is reduced by the buildup of cognitive reserves during life-course. Accumulation of proxies for cognitive reserve in early and late life had the greatest effect on dementia risk reduction. Social connection may be an effective approach to lower dementia risk.

A lifetime perspective on risk factors for cognitive decline with a special focus on early events

Both Alzheimer's disease and vascular dementia are the result of disease processes that typically develop over several decades. Population studies have estimated that more than half of the risk for dementia is preventable or at least modifiable through behavioral adaptations. The association between these lifestyle factors and the risk of dementia is most evident for exposure in midlife. However, habits formed in middle age often reflect a lifetime of behavior patterns and living conditions. Therefore, individuals who, for example, are able to maintain healthy diets and regular exercise during their middle years are likely to benefit from these cognition-protective habits they have practiced throughout their lives. For numerous adult diseases, significant risks can often be traced back to early childhood. Suboptimal conditions during the perinatal period, childhood and adolescence can increase the risk of adult diseases, including stroke, heart disease, insulin resistance, hypertension and dementia. This review aims at summarizing some of the evidence for dementia risks from a life-time perspective with the goal of raising awareness for early dementia prevention and successful aging.

Neuromuscular Dysfunction Precedes Cognitive Impairment in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) develops along a continuum that spans years prior to diagnosis. Decreased muscle function and mitochondrial respiration occur years earlier in those that develop AD; however, it is unknown what causes these peripheral phenotypes in a disease of the brain. Exercise promotes muscle, mitochondria, and cognitive health and is proposed to be a potential therapeutic for AD, but no study has investigated how skeletal muscle adapts to exercise training in an AD-like context. Utilizing 5xFAD mice, an AD model that develops ad-like pathology and cognitive impairments around 6 mo of age, we examined in vivo neuromuscular function and exercise adapations (mitochondrial respiration and RNA sequencing) before the manifestation of overt cognitive impairment. We found 5xFAD mice develop neuromuscular dysfunction beginning as early as 4 mo of age, characterized by impaired nerve-stimulated muscle torque production and compound nerve action potential of the sciatic nerve. Furthermore, skeletal muscle in 5xFAD mice had altered, sex-dependent, adaptive responses (mitochondrial respiration and gene expression) to exercise training in the absence of overt cognitive impairment. Changes in peripheral systems, specifically neural communication to skeletal muscle, may be harbingers for AD and have implications for lifestyle interventions, like exercise, in AD.

Healthy lifestyle and cognitive aging: What is the gap behind prescribing healthier lifestyle?

Although there is a clear link between lifestyle and cognitive health, the dissonance between observational and intervention studies results reveals gaps in the knowledge of how to translate healthy lifestyles into better cognitive health for the population. This letter discusses gaps in interpreting observational studies linking healthy lifestyles and cognitive health in older adults. The main goal is to briefly highlight the necessity of understanding and incorporating intrinsic and extrinsic drivers of engagement in healthy lifestyles before prescribing and implementing individual and multicomponent programs.