Association between physical activity and the prevalence of metabolic syndrome: from the Korean National Health and Nutrition Examination Survey, 1999–2012
It is well known that physical activity has favorable effects toward preventing metabolic syndrome. This study investigated not only the association between risk components of metabolic syndrome and physical activity type and frequency, but also examined the association between the prevalence of metabolic syndrome and physical activity according to type and frequency of physical activity.
The main finding of this study is that physical activity reduces the prevalence of metabolic syndrome. The lowest prevalence of metabolic syndrome was investigated in those participants who walked six times per week (OR 0.67, 95% CI 0.53–0.85). Several studies have previously determined the association between physical activity and the prevalence of metabolic syndrome, by examining the amount of physical activity during a physical activity (Laaksonen et al. 2002; Ekelund et al. 2005). The added value of this study is that it provides detailed support for that relationship, and also provides a more specific examination of the frequency and type of physical activity. Laaksonen et al. (2002) investigated the association between time spent (3 h/week) doing moderate and vigorous physical activity and the prevalence of metabolic syndrome, as measured by self-reported data. Similar to this study, participants who participated in vigorous physical activity, and were in the upper third of the VO2max range, had an even stronger inverse association with the occurrence of metabolic syndrome. Ekelund et al. (2005) found a dose–response association between physical activity energy expenditure, including all daily activity, regardless of physical activity type and the metabolic syndrome. Whereas, in this study the finding was a dose–response association between physical activity and the prevalence of metabolic syndrome, and provided detailed supporting analyses covering main five-physical activity types.
Another main finding was that the measured levels of risk components of metabolic syndrome improved as subjects participated in vigorous physical activity, moderate physical activity, walking, strength, and flexibility, when compared with subjects who did not participant in physical activity. As the frequency of physical activity increased, the level of risk components of metabolic syndrome decreased in walking with fasting blood glucose, moderate physical activity with HDL cholesterol, and vigorous physical activity, strength, and flexibility with waist circumferences. In general, physical activity can be considered an effective prevention and treatment for metabolic syndrome, noting that each component of metabolic syndrome is impacted uniquely depending on the specific type and frequency of physical activity. As a guideline, vigorous physical activity at least once per week and regular physical activity of moderate, walking, strength, and flexibility for more than three times a week might be recommended for reducing the prevalence of metabolic syndrome.
All of the five types of physical activity had favorable effects toward increasing HDL cholesterol and reducing triglycerides. Varying the type and frequency of physical activity gives rise to different results as indicated in previous studies (Andersen et al. 1999; Johnson et al. 2007; Houmard et al. 2004; Gennuso et al. 2014). Generally, moderate to vigorous exercise was effective towards reducing triglyceride and body mass (Andersen et al. 1999). Jonson et al. (2007) provided additional support as to the amount and intensity of exercise needed to significantly improve factors related to metabolic syndrome and recommended that 30 min of moderate intensity exercise be participated in every day, when the objective is to reduce the prevalence of metabolic syndrome. Similarly, Houmard et al. (2004) reported that moderate intensity exercise resulted in better triglyceride responses and insulin sensitivity, when compared with vigorous intensity exercise. Gennuso et al. (2014) found that increased amounts of sedentary time were associated with an increased risk of metabolic syndrome, including triacylglycerol, HDL-cholesterol, and fasting glucose. Also, this study found favorable effects on fasting blood glucose from even walking once per week, in addition to everyday walking and vigorous physical activity. Aerobic capacity, musculoskeletal, and hemodynamic improvements were achieved by greater duration and intensity or physical activity, and even a relative low frequency of physical activity (10 min walking three times per week) improved fasting plasma glucose (Yates et al. 2013; Foulds et al. 2014).
An interesting finding from this study was that waist circumferences decreased for all types of physical activity, however waist circumferences were not decreased with walking (for once per week to four times per week). The indication is that walking may be too low in intensity to reduce the waist circumference. In a similar study, Chang et al. (2015) measured waist circumferences of 628 senior adults, in order to investigate a combined association among body compositions, metabolic syndrome factors, and physical fitness characteristics and found that the occurrence of metabolic syndrome was positively associated with reduced flexibility (OR 0.9, 95% CI 1.25–2.07). Additionally, a finding of this study was that participants who did flexibility physical activity three times a week, had a decreased occurrence of metabolic syndrome (OR 0.76, 95% CI 0.65–0.88). We would suggest that flexibility should be an indicator of evaluation for metabolic syndrome and found that increased physical fitness levels caused other metabolic risk factors to decrease.
Physical activity helps that these metabolic factors were systolic blood pressure, when participating in walking and strength at least two times per week; and diastolic blood pressure during vigorous physical activity, when participated in only once per week or three times per week. For other types and frequency of physical activity, this study could not find significant changes. Although blood pressure in this study did not find similar significant correlations in examining other components of metabolic syndrome, other previous study did hold that physical activity was strongly recommended for patients who had atherosclerotic cardiovascular disease, in order to better manage blood pressure due to resultant improved lipoprotein profiles, including LDL-cholesterol and HDL-cholesterol (Smith et al. 2009; Sang et al. 2014).
Additional analysis was conducted to find differences in the relationship between exercise and metabolic syndrome based on sex. The result showed that there was a similar association between physical activity and prevalence of metabolic syndrome. However, a major difference was found in the triglyceride levels. Women had about a 50 mg/dL lower triglyceride level than men at baseline. The men who did not participate in exercise had over 150 mg/dL, which is a borderline for metabolic syndrome. On the other hand, the men who participated in vigorous exercise, moderate exercise and strength exercise over 4 times per week and walking for over 6 times per week were found to be under the triglyceride borderline level. Similarly, Wood et al. (1991) reported that a 12 month exercise intervention program with dietary modifications reduced triglyceride levels by 30% in men and 2% in women. Also, Brownell et al. (1982) found higher beneficial effects of exercise (after a 10 week program) on triglyceride in men than for women. We confirmed that Korean men might receive a higher benefit from participation in physical activity towards amending the triglyceride level than women, among the metabolic syndrome components.
The mechanism behind the effects of physical activity on metabolic syndrome might be related to a resultant reduction in the level of inflammation grade. Although intense physical activity invokes pro-inflammatory cytokines, a possible explanatory mechanism is that physical activity improves body composition, dyslipidemia and endothelial function, increases anti-inflammatory cytokines, decreases body fat, and decreases the expression of adhesion molecules (Powers and Hamilton 1999; Green et al. 2004; Kasapis and Thompson 2005).
The strength of this study is that it identifies the healthier frequencies of physical activity and distinguishes which type of physical activity should be conducted to better reduce the risk of metabolic syndrome. The study findings serve to provide key guidance for reversing the prevalence of metabolic syndrome based on type and frequency of physical activity, by employing a large representative sample. In this way the study was able to disentangle the effects of physical activity in five different types of physical activity, while looking across various frequencies of physical activity. The strength of the sampling methodology is supported by the use of KHANES data that is a valid and reliable countrywide database. The data analysis approach used statistical analyses that employed a stratified multistage sampling design.
There are several study limitations that need to be addressed. First, the type and frequency of physical activity in this study were measured by using a self-reporting style IPAQ survey instrument, and it is noted that self-reported data could lead to misclassification and measurement error. To address that weakness, a trained investigator conducted the survey, and this approach has been validated in previous studies. Second, this study does not infer causality between type and frequency of physical activity and the prevalence of metabolic syndrome, because this study used a cross-sectional design. Third, the Korean National Health and Nutrition Examination Survey did not provide detailed data related to the use of specific medications. As such, this study was unable to identify the relationships associated with those factors. Fourth, An important idea to grasp is that if a study is very large, its result may be statistically significant, however, that level of deviation from the null hypothesis may be too small to be of any clinical interest. That is, the statistical difference is too small to warrant a change or modification to current clinical practices or to the current standardized treatment programs. Lastly, physical activity intensity, frequency, and type should be more detailed in order to explain the exact mechanisms and associations between physical activity and metabolic syndrome.
In conclusion, physical activity was found to be associated with the components of metabolic syndrome and with the prevalence of metabolic syndrome. It was found that the effects of physical activity varied significantly depending on the type and frequency of the physical activity participation. Regular physical activity and the avoidance of physical inactivity are key principles for the prevention of metabolic syndrome. When patients are diagnosed with metabolic syndrome, it is important to check the underlying risk components related to metabolic syndrome. From that information, better recommendations can be made that address specific physical activity types and frequencies that could benefit the patient in their efforts to reverse the condition of metabolic syndrome.