The current study established that objective light physical activity offers a protective effect from future decline in cognitive abilities over approximately two years among community dwelling older adults. The protective effects of light physical activity were independent of MVPA and the results remained robust in sensitivity analyses removing those people with difficulties with ADL, depressive symptoms and suspected mild cognitive impairment at baseline.
With the rapidly growing number of older people across the world, our data that objective light physical activity confers a protective effect for future cognitive abilities are welcome and has potential public health implications. Previous reviews (Blondell et al. 2014; Hamer and Chida 2009; Paterson and Warburton 2010) have repeatedly highlighted the absence of studies considering objective physical activity data and future cognitive impairment. Thus, the overwhelming reliance of self-report physical activity from previous studies has infiltrated a bias within the literature and such questionnaires cannot accurately disentangle the potential individual benefits of different intensities of physical activity. The unique protective influences of light physical activity on cognition are welcome for a number of reasons. First, light physical activity such as casual walking, gardening and household chores are a preferred method of accumulating physical activity for older people (Farren et al. 2015). Moreover, light physical activities may also offer opportunities to interactive with neighbors, families
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and friends and reduce the risk of social isolation. In addition, light physical activity is associated with better wellbeing, physical health (Buman et al. 2010; Ku et al. 2016) and improvements in other health outcomes such as reducing blood pressure, body fat, cholesterol and improving cardiorespiratory fitness (Hanson and Jones 2015). Moreover, the risk of injury and adverse outcomes are typically less with light physical activity versus more vigorous intensities (Paterson and Warburton 2010). However, there are clearly benefits for engaging in higher intensity physical activity and our data also establish that MVPA has a protective effect on future cognitive impairment. In particular, higher intensity physical activity that improves cardiorespiratory fitness confers particular benefits on health and brain function (Erickson et al. 2014; Erickson et al. 2012).
The potential mechanisms by which physical activity confers a cognitive benefit in older age are yet to be fully disentangled. One potential mechanism is through improving brain structure and grey matter volume and in particular stimulating hippocampal neurogenesis, with more recent evidence also suggesting the caudate nucleus and thalamus may be positively impacted (Erickson et al. 2014; Erickson et al. 2012; Erickson et al. 2011; Kramer and Erickson 2007). There is also accumulating evidence that participating in exercise may improve cognitive outcomes through numerous biomarkers. In particular, recent data suggests that brain-derived neurotrophic factor, cholesterol, testosterone, estradiol,
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dehydroepiandrosterone may be associated with improved cognition and reduced dementia risk following exercises in older age (Jensen et al. 2015; Maass et al. 2016). Clearly, future research utilizing objective measures of physical activity are required to disentangle potential mechanistic changes associated with cognitive status in older age.
Whilst our data are novel, one should note the observation nature of the data, which cannot make claims regarding causality. The study follow up time was relatively short. Future longitudinal research of longer duration is required to verify our findings. In addition, future interventional work should seek to establish if changing physical activity levels can improve cognitive (and other) outcomes. Another potential limitation is that objectively assessed physical activity was only measured at baseline, which clearly limits the ability to explore the reciprocal relationships between light physical activity and cognitive ability. Furthermore, there is heterogeneity of comorbid conditions or health status in the population aged 65 or above (e.g., different age groups). Future studies are encouraged to assess the relationships of objectively measured physical activity with cognition, stratified by age groups. In addition, we included some participants at baseline who had some degree of cognitive impairment, which may influence the physical activity status at baseline. However, the independent impact of light physical activity was evident in sensitivity analyses when such participants were removed to mitigate the possibility of reverse causation. Moreover, presenting the data
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with and without such participants may actually increase representativeness, given the high numbers of older people who are affected by cognitive impairment. This is the first longitudinal paper to investigate light intensity physical activity and cognitive ability in older adults. Strengths of our paper include the objective measurement of physical activity, adjustment for multiple underlying confounders (e.g. baseline cognitive status, depressive symptoms, and ADL difficulties) known to influence both physical activity and cognitive ability, and test for reverse causation.
In conclusion, our data suggest that engagement in light intensity physical activity, independent of MVPA, is associated with a reduced rate of cognitive ability decline in community dwelling older adults. In addition, objectively assessed MVPA is associated with better cognitive status. This extends the existing evidence for the benefits of physical activity for preventing cognitive decline/impairment in older adults.
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Acknowledgements
The authors declare no conflicts of interest and acknowledge funding support from Taiwan Ministry of Science and Technology (104-2410-H-018-028).
Conflict of interest statement
The authors confirm that there are no financial conflicts of interest associated with this paper.
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29
Highlight Points
A paucity of studies have considered objective longitudinal physical activity and future
cognitive ability decline in older adults.
Our data suggests that higher light physical activity, independent of
moderate-to-vigorous physical activity, is associated with a reduced risk of future cognitive decline.
This is the first longitudinal paper to investigate light intensity physical activity and cognitive decline in older adults.
This extends the existing evidence for the benefits of physical activity for
preventing cognitive deterioration in later life.