INTRODUCTION
Dementia is a major health problem in the elderly with estimated 46.8 million people affected worldwide in 2015. The prevalence of dementia is also estimated to be close to 50 million people in 2017 and to double every 20 years, reaching 75 million in 2030 and 131.5 million in 2050 [1]. The cognitive functional decline is observed in most elderly people. Previous epidemiological studies suggested that cognitive decline is associated with development of dementia. Annually, 10–15% of older people with mild cognitive impairment progress to dementia compared with 1–2% of older people with normal cognition [2,3].
Previous studies suggests that higher physical activity are associated with prevention of the decline in cognitive function and reduced risk of dementia with aging [4-6]. In addition, changes in physical activity may contribute to age-related changes in biological vitality and physical function. Moreover, higher levels of physical activity is associated with a decreased risk of cardiovascular disease, all-cause and cardiovascular mortality, physical function decline, and frailty [7-10]. Therefore, physical activity may also have an effect on the risk of cognitive dysfunction.
Previous studies have investigated the association between physical activity and cognitive functions. However, only a few examined the associations between physical activity and cognitive function in the Korean population. Additionally, to our knowledge, physical activity level recommended by current guidelines for Korean adults has not been reported as a potential predictor of cognitive dysfunction in the older Korean adults. Therefore, we aimed to investigate whether physical activity is associated with the risk of cognitive dysfunction in the elderly Korean population.
METHODS
Study Participants
The present study used the data from the Korean Longitudinal Study of Ageing (KLoSA), a national survey of adults aged ≥ 45 years [11]. The KLoSA was started in August 2006, and 10,254 subjects completed the baseline survey interview using computer-assisted personal interviewing method. In this study, we selected 4,165 participants aged ≥ 45 years, and 1,077 subjects were excluded due to missing data for physical activity, cognitive function score, and other covariates. For this analysis, a total of 9,177 subjects were included. All subjects provided written informed consent, and the study protocol was approved by the Institutional Review Board of the Korea Employment Information Service.
Assessment of Physical Activity
The total volume of physical activity was assessed using a questionnaire. All subjects were asked to record the frequency of physical activity (times per week) and duration (min). Time spent being physically active was calculated considering frequency and duration in minutes per week. The subjects were categorized into three groups by total physical activity time: inactive (none), < 150 min per week, and ≥ 150 min per week based on the current physical activity guidelines for Korean adults [7,12].
Cognitive Function
Cognitive function was assessed using the Korea-Mini Mental Status Evaluation (K-MMSE). The K-MMSE comprises five areas, including registration, orientation, memory, attention and calculation, and language [13,14]. We categorized subjects into normal cognitive (K-MMSE ≥ 24) and cognitive dysfunction (K-MMSE < 24) groups [15].
Confounding Factors
Age, sex, education level, smoking status, and medical health conditions (depression, hypertension, diabetes, cardiovascular disease, and cancer) were considered as potential confounders. We categorized education levels as < high school, high school, or > high school. Smoking status was defined as never, former smoking, and current smoking. Medical health conditions were assessed using self-reported questionnaire.
Statistical Analysis
We analyzed all dataset using SPSS software (PASW Statistics 18 for Windows, IBM Inc., Chicago, IL, USA), and the results were considered statistically significant with P-values < 0.05. The subjects’ characteristics are expressed as mean ± standard deviation (SD) for continuous variables and sample size (%) for categorical variables. We analyzed the characteristics of study participants by physical activity levels using the ANOVA for continuous variables and Chi-squared tests for categorical variables. Multivariable logistic regression models were used to assess the association of physical activity levels and the risk of cognitive dysfunction. We also developed three sequential models to test the effect of confounding factors on the association between physical activity and cognitive dysfunction: 1) adjusted for age and sex; 2) additionally adjusted for education level and smoking status; 3) additionally adjusted for depression, hypertension, diabetes, cardiovascular disease, and cancer. In addition, we conducted sensitivity analysis using separated model by age group (< 65 years and ≥ 65 years) and sex.
RESULTS
In Table 1, characteristics of the participants are presented. The mean age was 61.04±10.91 years. Overall, 44.55% of participants were men, and 55.45% were women. The mean cognitive function sore was 24.56±5.93. Table 2 shows the characteristics of study participants by physical activity level. We found significant differences in age, cognitive function score, and prevalence of cognitive dysfunction (all P<0.001, Table 2).
Table 3 shows the results of multivariable odds ratio (OR) and 95% confidence interval (CIs) for the risk of cognitive dysfunction by physical activity levels. Levels of physical activity were significantly associated with a reduced risk of cognitive dysfunction after adjustment for age and sex. The results were not changed after additionally adjusted for education level and smoking status. In fully adjusted model, we also found significant association between physical activity levels and cognitive dysfunction (Table 3, model 3). We also found consistent results when investigated these associations using stratified model according to sex and age group (Table 4).
DISCUSSION
In this study, we investigated the association between physical activity levels and the risk of cognitive dysfunction in the Korean population. Our findings suggest that higher level of physical activity is significantly associated with a lower risk of cognitive dysfunction independent of clinical health conditions and other potential confounding factors. Moreover, sensitivity analysis using stratified model by age group and sex also showed similar association between higher levels of physical activity and decreased risk of cognitive dysfunction. These findings suggest that low physical activity may be a risk factor for cognitive function decline in the general Korean population.
In the present study, the prevalence of cognitive dysfunction was approximately two times higher in participants with the lowest levels of physical activity compared to those with the highest physical activity levels. The present study is the first investigation that confirmed the association of physical activity and cognitive dysfunction in the middle-aged and older Korean populations. The results of our study are consistent with previous reports showing that physical activity is associated with risk of cognitive dysfunction and mild cognitive impairment [16-19]. For example, a study on the community-dwelling older adults reported that daily physical activity was associated with cognitive function variability in the elderly [20]. In addition, 28-year follow-up study analyzed using Whitehall II cohort reported that lower levels of physical activity was associated with an increased risk of dementia in the elderly [21].
Biological ageing contributes to the changes in nervous system function, which could explain the association of physical activity and cognitive decline during aging process [22]. A decline in the function of the central nervous system with aging may be an important mechanism underlying the association of physical activity and cognitive dysfunction. In fact, a slow reaction is associated with decreased cognitive function in the older adults [23]. Moreover, another systematic review and meta-analysis reported a longitudinal association of physical activity and changes in cognitive abilities [19]. Thus, physical activity might contribute to prevention of age-related decrease in the central nervous system function, which is reflected in cognitive dysfunction.
Previous epidemiological studies have described the association between physical activity and cognitive dysfunction. Our results are consistent with several recent studies, in which physical activity was associated with a risk of cognitive dysfunction in the older population. However, there remains a lack of information about the effect of physical activity on the risk of cognitive dysfunction in the middle-aged population. Therefore, in this study, we also investigated the association of physical activity levels and the risk for cognitive dysfunction using stratified model, and we observed no difference between the middle-aged and older populations. These findings suggest that physically active lifestyle may prevent cognitive decline with ageing even in middle-aged adults. However, further longitudinal and intervention studies are necessary.
Strengths and Limitations
Several limitations of this study should be acknowledged. In the present study, the primary limitation is that we cannot infer causal effect of physical activity on the risk of cognitive dysfunction because of the cross-sectional design. Moreover, we assessed the total volume of physical activity but not each type, such as intensity and domain specific activity parameters, that may predict cognitive decline [24-26]. However, our study included a large nationally representative sample of Korean adults, and our analyses were considered for important confounding factors. Thus, our findings can be generalized to the Korean population. However, the level of physical activity in Koreans is still insufficient, and the amount of physical activity has been decreasing during the past decade [27]. Recently, a systematic review showed that physical activity intervention may help to improve cognitive function in the middle-aged adults [28-30]. Therefore, our findings of this study are important for public health strategies aimed at preventing cognitive dysfunction in the Korean population.
PDF Links
PubReader
ePub Link
XML Download
Full text via DOI
Download Citation
Print
