Page 12 - 《运动与健康科学》(英文)2024年第2期

TaggedAPTARAEnd134 M. Rodriguez-Ayllon et al.
by severe progressive memory impairments related to deposition positive and 2 null associations). In 2019, Frederiksen et al. 21
of amyloid beta (Ab) plaques in brain extracellular spaces causing carried out a systematic review of observational studies to
2
cortical dysfunction and neuronal loss. Ab accumulation can be explore the association of physical activity with AD
detected in a preclinical stage of AD, before clinical symptoms biomarkers. In brief, they concluded the majority of the identi-
3
emerge, and can be measured in the brain and the cerebrospinal fied studies did not find a significant association between phys-
fluid (CSF) via positron emission tomography (PET) and lumbar ical activity and Ab. 21 This, together with the lack of
4
puncture, respectively. Several studies indicated an inverse corre- quantitative synthesis of data (e.g., a meta-analysis), and the
lation between global cortical amyloid PET and CSF Ab fact that literature in the field has grown substantially over the
levels. 57 One of the hypotheses is that Ab levels gradually past few years, has limited the ability of prior work to draw
decrease in the CSF in AD because of the preferential sequestra- solid conclusions about the effect of physical activity on Ab in
5
tion as insoluble deposits in brain. Recently, an increasing humans. Consequently, an updated systematic review is needed
number of studies have also explored blood Ab as a blood to understand the role of physical activity on Ab levels—and it
biomarker for AD. However, the published results regarding the must include both intervention studies, to provide causal
correlation of blood Ab with brain and CSF Ab are conflicting, evidence, and observational studies, to provide complementary
and many factors have been reported to impact blood Ab levels information in an emerging field that is still in its infancy.TaggedAPTARAEnd
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and their association with AD biomarkers. TaggedAPTARAEnd TaggedAPTARAPTherefore, the aim of the current systematic review was to
TaggedAPTARAPPotentially modifiable factors (e.g., lifestyle factors) have determine the overall effect of physical activity on Ab by
garnered increased attention as possible approaches for conducting a systematic review and meta-analysis of available
reducing Ab accumulation in the brain and, in turn, delaying intervention studies (including randomized controlled trials
9
the progression of AD. Animal models indicate that physical (RCTs) and non-RCTs). Due to the expected lack of interven-
activity may delay, prevent, or treat AD by impacting Ab tion studies, we also aimed to synthesize the observational
plaque deposition. 1012 In humans, researchers have used evidence by conducting a meta-analysis of observational
several measurements of Ab in the brain, CSF, and blood to studies (including cross-sectional and prospective longitudinal
explore the effects of physical activity on Ab levels. However, studies) testing the association between physical activity and
the results obtained were inconsistent. 1317 For instance, some Ab in middle-aged and older adults.TaggedAPTARAEnd
intervention studies have found that the level of Ab in the brain
does not change after a physical activity intervention. 13,14
TaggedAPTARAH12. MethodsTaggedAPTARAEnd
15
Similar results were found by Jensen et al., who concluded
that physical activity did not affect CSF Ab after a 16-week TaggedAPTARAPThis study was conducted in accordance with Preferred Reporting
intervention. In contrast, other studies established that physical Items for Systematic Reviews and Meta-Analyses (PRISMA)
22
activity reduces the levels of blood circulating Ab. 16,17 There guidelines. Additionally, the systematic review protocol
are several possible explanations for these inconsistencies, was registered in the international Prospective Register of
including the study design, population characteristics, or Ab Systematic Reviews (PROSPERO) (CRD42020184203).TaggedAPTARAEnd
measurement. Therefore, a systematic synthesis of the current
evidence that considers potential moderators is needed to TaggedAPTARAH22.1. Search strategyTaggedAPTARAEnd
confirm or refute the hypothesis that physical activity modu- TaggedAPTARAPThe literature search was carried out from inception to April
lates Ab levels. Clarity on this issue would improve our under- 28, 2022 in PubMed, Web of Science, PsycINFO, Cochrane
standing of whether Ab modulation is one of the mechanisms Central Register of Controlled Trials, and SPORTDiscus. The
through which physical activity might decrease dementia risk. search strategy used for all databases is described in Table 1.
This knowledge would no doubt contribute to the development We extracted all studies from the different databases into an
of more effective physical activity interventions for reducing EndNote Library (Version X7; Clarivate, Philadelphia, PA,
USA). Relevant articles were screened by titles and abstract
cognitive decline in older adults.TaggedAPTARAEnd
TaggedAPTARAPTwo previous narrative reviews have explored the relation- by 2 independent researchers (CAA and MAO). Full-text

ship between physical activity and Ab. 18,19 Specifically, Ebra- articles considered acceptable for review were examined to
himi et al. 18 suggested that physical activity could improve determine final eligibility by the same 2 researchers (CAA and

cognitive function by reducing Ab levels. In contrast, Brown MAO). In case of disagreement, consensus was achieved
et al. 19 concluded that although evidence in animals seems through discussion and, when required, the opinion of a third
consistent, evidence of the influence of physical activity on Ab
researcher (MRA) was considered.TaggedAPTARAEnd
in humans is still scarce. While these reviews contributed
important insights to the field, the absence of objective and
TaggedAPTARAH22.2. Eligibility criteriaTaggedAPTARAEnd
systematic study selection criteria arguably leads to a number
of methodological biases (e.g., the author’s interpretation and TaggedAPTARAPOverall, the inclusion criteria were: (a) age criterion: adults
conclusions). In 2015, de Souto Barreto et al. 20 performed a aged 45 years and older; (b) language criterion: no restrictions; (c)
systematic review to explore the association of physical activity exposure: physical activity; for experimental studies, physical
and AD biomarkers, including Ab, in humans. However, exercise interventions (a form of physical activity that is planned,
evidence at that time was limited. Only 5 cross-sectional studies structured, repetitive, and performed to improve health or fitness)
were included, and their results were contradictory (i.e., 3 not combined with another type of intervention (e.g., cognitive/