Aerobic exercise reduced the risk of cognitive impairment
and dementia which can be explained by either a direct neurotrophic
effect of exercise or by an improvement in the cerebrovascular
and cardiovascular risk profiles. The authors argue that
aerobic exercise attenuates progression of neurodegenerative
processes and age-related loss of synapses and neuropil via facilitation
of neurotrophic factors and neuroplasticity (30). These
findings are in line with animal experiments in which aerobic
exercise enhances hippocampal dendritic length and dendritic
spine complexity (31). In a long-term, prospective cohort study,
the usual weekly walking distances reported by healthy adults at
baseline were positively associated with neocortical and hippocampal
MRI volumes 9 yr later (32). Recently, Rovio et al. (33)
reported that leisure-time PA at midlife (on average 21 yr before
the diagnosis of dementia) is related to a decreased risk of dementia
and AD. Individuals participating at least twice a week
in a leisure-time PA had 50% lower odds of dementia compared
with sedentary persons.