Page 19 - 《运动与健康科学》(英文)2024年第2期

TaggedAPTARAEndPhysical activity and amyloid beta 141
physical activity on the brain and CSF Ab. In observational further studies might explore whether the effect of physical
studies, the association of physical activity with brain and activity on Ab varies by type of intervention.TaggedAPTARAEnd
blood Ab was not significant, but higher levels of physical
activity were positively associated with Ab in the CSF.TaggedAPTARAEnd
TaggedAPTARAH24.2. Meta-analyses of observational studies: The associations
between physical activity and AbTaggedAPTARAEnd
TaggedAPTARAH24.1. Meta-analysis of intervention studies: The effects of
TaggedAPTARAPMeta-analyses of observational studies in middle-aged and
physical activity on AbTaggedAPTARAEnd
older individuals indicated that physical activity was signifi-
TaggedAPTARAPOur intervention meta-analysis identified that physical cantly associated only with CSF Ab. However, these results
activity moderately reduces the levels of blood Ab in middle- should be interpreted with caution because most studies
aged and older individuals. However, the results were not statis- included in the meta-analyses were of a cross-sectional design.
tically significant, and the number of studies assessing Ab only Of the 4 longitudinal cohort studies included in this systematic
in the blood in the final meta-analyses was limited. The review, 2 were performed in cognitively normal older
published results regarding the correlation of blood Ab with adults, 38,39 while the other 2 were carried out in individuals
brain and CSF Ab are conflicting, and its effect on other AD with mild cognitive impairment 40 or Down syndrome. 37
8
biomarkers is still unclear. Altogether these findings make it Notably, the 2 studies focused on individuals with cognitive
37,40
difficult to conclude whether physical activity could be a protec- impairments did not find any significant association. A
tive factor for AD through its effect on Ab.Weare not possible explanation for this could be that physical activity is
suggesting that physical activity does not positively affect cogni- less influential in individuals whose accumulation of Ab in the
tive health in older adults, just that there are other possible brain reaches a certain threshold. Of note, longitudinal PET
mechanisms, such as exercise-induced changes in the expression studies in humans have demonstrated that Ab accumulates
of neurotrophic factors and neurotransmitters, that might explain slowly and plateaus at the onset of clinical symptoms. 6466 The
the protective role of physical activity in neurocognitive health plateau of Ab may indicate that amyloid pathology reaches
during late adulthood. 63 Additionally, it is important to note that dynamic equilibrium or inactivity at the clinical stage of
several questions remain unanswered at present. First, the effect dementia. Although we observed a tendency in favor of this
of physical activity on Ab might differ between cognitively hypothesis, population characteristics of included studies (cogni-
normal and cognitively impaired people as well as in younger tively normal vs. cognitively impaired) did not moderate the
and older adults. In this regard, animal studies 19 suggest that relationship between physical activity and Ab in our meta-analy-
physical activity might only be effective in reducing Ab accu- sis. Overall, further prospective population-based cohort studies
mulation within an early preclinical stage. Accordingly, individ- are needed to provide greater insight on the longitudinal associa-
uals who are already experiencing deterioration in cognitive tion between physical activity and Ab by comparing (a) preclini-
function may be too advanced in the disease course for physical cal and clinical stages of AD, and (b) individuals of different
activity to modify Ab deposition. However, in our meta-analy- ages and cognitive characteristics.TaggedAPTARAEnd
sis, we were surprised to observe higher effects in older people, TaggedAPTARAPIn addition to the participants’ characteristics, other differen-
which is out of line with this hypothesis. Altogether, due to the ces (e.g., the instrument used to assess Ab measurements in
contradictory findings, the heterogeneity between studies, and the brain, CSF, or blood) might be considered. For instance,
the low number of studies included in our meta-analysis, more gold-standard measurements, such as PET, offer the most accu-
intervention studies are needed to develop a full picture of the rate way of evaluating the relationship between physical activity
role of age and cognitive health status in the effects of physical and brain Ab levels antemortem. However, despite its advan-
activityonAb in both middle-aged and older adults. Second, tages, PET scanning is not able to quantify small changes in
the measurements of Ab were heterogeneous (only a single brain Ab, especially over short periods, which could partially
study used brain Ab, 14 1 study used CSF Ab, 15 and6used explain the null associations. 67 In contrast, other Ab biofluid
blood Ab 17,3135 ). Because of the heterogeneity between studies, markers in the CSF seem to be more sensitive and dynamic
only studies that assessed Ab in the blood were included in the indicators of the relationship between physical activity and Ab
meta-analysis. Thus, additional well-designed RCTs with a stan- in human populations, 68 which could partially explain our find-
dardized Ab measurement protocol are needed to confirm or ings. In addition to CSF and brain Ab, there has been a growing
refute the effects of physical activity on brain, CSF, and blood interest in developing new techniques to measure blood Ab due
Ab levels in cognitively normal and cognitively impaired indi- to its being a less expensive and invasive approach. However,
viduals. Third, the effects of physical activity on Ab became until recently, most studies exploring the association between
significant and the total effect size increased when the study physical activity and blood Ab have used ELISA kits, which
carried out by Kim et al. 33 (which assessed Ab 30 min after the showed high variability. 19 This issue might be attenuated by
final session in the 16th week) was excluded from the meta-anal- using high-performance blood-based Ab assays, such as mass
4
ysis. Consequently, future studies might explore the acute spectrometry. Remarkably, differences were also found in the
and chronic effects of physical activity on Ab by standardizing direction of the associations between physical activity and the
the time interval between the final session of the physical various measurements of Ab. Specifically, the relationship
activity intervention and the post-intervention Ab assessment. between physical activity and CSF Ab was positive, which is
Lastly, our meta-analysis also suggested the type of intervention contrary to what was expected in the brain. Although more
(i.e., aerobic vs. others) might affect Ab differently. Therefore, accurate assays are needed to understand whether physical