Physical Activity as a Moderator of Alzheimer Pathology: a Systematic Review of Observational Studies.

Introduction: Observational studies have found that physical activity is associated with a reduced risk of cognitive decline and dementia. Whether physical activity may also reduce the level of AD pathology, remains undetermined. Objective: To examine the relationship between physical activity and AD biomarkers (beta-amyloid1-42, total tau and phosphorylated tau in CSF, amyloid PET, hippocampal atrophy on MRI and parietotemporal hypometabolism on brain 18F-FDG-PET). Methods: We carried out a systematic review of the observational studies of physical activity and AD biomarkers in healthy subjects, subjective cognitive complaints, mild cognitive impairment (MCI) and AD dementia. Results: We identified a total of 40 papers, which were eligible for inclusion. Thirty-four studies were conducted on healthy subjects, 3 on MCI and healthy subjects, 1 on MCI, and 2 on AD and healthy controls. Six studies reported on CSF biomarkers, 9 on amyloid PET, 29 on MRI and 4 on brain 18F-FDG-PET. The majority of studies did not find a significant association between physical activity and AD biomarkers. Conclusion: The quality of included studies with only a few longitudinal studies, limits the conclusions which may be drawn from the present findings especially regarding the biomarkers other than hippocampal volume. However, the majority of the identified studies did not find a significant association.