This study was a meta-analysis; researchers analyzed the data reported in multiple independent research studies. To find relevant scientific articles, researchers performed an online literature search in different scientific databases. They used various keywords related to physical activity and cognitive decline (e.g., ‘physical exercise’, ‘fitness’, ‘training’; ‘cognitive impairment’, ‘cognitive loss’). Research papers were included in the present study if they met a number of criteria. For example, if at study baseline participants did not have dementia, and if the study included data on physical activity and cognitive ability. The researchers excluded studies that did not report associations between physical activity and cognitive decline, among other criteria.
Fifteen research papers were included in the study based on these parameters. The studies were carried out by researchers from many countries worldwide: Canada, the United States, the United Kingdom, Australia, several Asian countries (China, Singapore), and several European countries (Germany, Italy, and the Netherlands). The age of the participants included varied between studies. Almost all of the studies included only older participants. Some studies included people aged 55 years and older. Some studies included participants over the age of 65 or 85. One study included younger participants, aged 35 to 55.
The number of participants in each of the fifteen studies ranged from 66 participants to over 10,000 participants. Twelve studies had less than 3500 subjects. The remaining three studies had over 3500 participants. The number of years of follow-up varied from study to study, ranging from one to twelve years. Some studies included only female participants, some only male participants, and the majority of the fifteen studies included both female and male study participants. When the original study reported results for female and male participants separately, these data were kept as separate entries in the current meta-analysis.
In many of the studies, cognitive decline was measured using a psychological test that is commonly used in elderly populations to measure global cognition. This test measures cognitive abilities related to orientation, attention, memory, language, and visual-spatial abilities. Physical activity was assessed by administering questionnaires to participants. In some studies, the questionnaires were self-administered by the participants. The number and type of physical activity categories that participants could choose from varied for each study. Some studies used two or three categories such as low, medium, or high levels of physical activity. Other studies used time-based categories for physical activity, where participants indicated whether they exercised more than or less than 4 hours per week, for example.
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Researchers performed statistical analyses on the data extracted from these fifteen published research studies to examine whether physical activity levels in study participants affected their risk of becoming cognitively impaired. Data from over 33,000 people who did not have dementia at study baseline were included in the analysis.
Over 3000 participants went on to develop cognitive impairments over the course of the reported follow up periods.
The effects of physical activity on cognitive performance
All levels of physical activity were associated with a decrease in the risk of cognitive decline during the follow-up periods. The protective effects of physical activity did not appear to depend on the number of exercise participants engaged in. The authors of this paper reported that high levels of physical activity were associated with a 38% decrease in the risk of a decline in cognitive performance compared to sedentary participants. Additionally, low to moderate physical activity levels were associated with a 35% decrease in the risk of a decline in cognitive performance.
Differences between women and men
The protective effects of physical activity may be greater in female participants than in male participants. In the research studies that had fewer participants, that included only female participants, and that had shorter follow up periods, there appeared to be a decreased risk of cognitive impairment compared with studies with a greater number of participants, that included male participants, and that had longer follow up periods. Additional research is required to establish the type, frequency, and intensity of physical activity that best protects against a decline in cognitive performance.
RELEVANCE OF THE STUDY
The benefits of physical activity on various aspects of health have been well studied. There is evidence in the scientific literature that exercise decreases the risk of developing high blood pressure, diabetes, cardiovascular disease, some types of cancer, and decreases the risk of becoming obese.
The results reported in this paper address a gap in the literature because the association between physical activity and cognitive ability has not been well-studied, and the studies that do exist have reported results that are not consistent. A previous report in the scientific literature with a study design similar to the present study design (analysis of data published in various scientific journal articles) has provided evidence that physical activity decreases the risk of developing Alzheimer’s disease and dementia. This study is the first of its kind – it analyzes data from several independent scientific research articles that examine the effects of physical activity on cognitive decline.