Background: Dementia is a devastating condition for older adults, with both modifiable (e.g., diabetes mellitus) and unmodifiable risk factors (e.g., APOE 4 allele). It remains unclear how, and to what extent, diabetes impacts dementia risk via both cerebrovascular and amyloid-␤ pathways. Objective: We conducted a quantitative meta-analysis to investigate the contribution of diabetes to incident dementia risk in people with 4 and, based on the vascular-related neuropathology of diabetes, whether the combination of these factors increases risk for vascular dementia versus Alzheimer's disease (AD). Methods: Systematic literature searches were conducted using EMBASE, MEDLINE, PsycINFO, and CINAHL databases. Pooled relative risk (RR) estimates were calculated using a random effects model, and subgroup analyses conducted across dementia subtypes. Results: Twelve studies were included, with a total of 16,200 participants. Considered concurrently, diabetes increased incident dementia risk an additional 35% for those with 4 (RR = 1.35, 95% CI = 1.13-1.63). Similar patterns were observed for AD and vascular dementia. Conclusion: Interventions to prevent co-morbid diabetes, and diabetes-related complications and neuropathological changes, may be one way of modifying dementia risk in the vulnerable 4 population.

Background: A relationship has been observed between physical activity and cognition in older-onset Parkinson's disease, as well as improvements in cognition after a physical activity intervention. To date, this has not been investigated in young-onset Parkinson's disease (YOPD). Objectives: To examine the baseline relationship between physical activity and cognition in YOPD; and to examine whether a physical activity intervention can improve cognition in YOPD. Methods: Two interrelated online studies were conducted. In the first study, 132 participants with YOPD completed self-reported measures of physical activity, and objective and subjective measures of cognition. A subset of 38 participants was then randomly allocated to either a six-week physical activity intervention or control condition. Following the intervention, participants repeated the objective and subjective cognitive measures. Results: No relationship was found between self-reported physical activity and objective cognition; however, there was a relationship between physical activity and subjective cognition. Similarly, following the intervention subjective improvements were found for concentration, attention, and processing speed, but not for memory. Furthermore, medium effect sizes were evident for objective measures of processing speed and small-medium effect sizes for planning and cognitive flexibility, although statistical significance was not reached. Conclusions: In this first study investigating physical activity and cognition in YOPD, the results suggest that increased physical activity relates to improved processing speed and attention. Replication is recommended with a larger sample size. A longer, more intense physical activity manipulation and utilizing the study's strengths of online recruitment and intervention delivery are also recommended.