This study identified the association between PA levels and MetS components in Korean adults, and compared the risks of MetS and abnormal MetS components in subjects who met the current PA recommendation and those who did not. Consistent with previous studies [7
], results of the present study suggest that subjects who participated in higher levels of PA and who met the current PA recommendations had significantly lower risks of MetS or abnormal MetS components compared to physically inactive individuals. These findings also extend the previous observation by Cho et al. [21
], who demonstrated that higher leisure-time PA is significantly associated with lower prevalence of MetS after accounting for confounding factors such as age, smoking status, and alcohol consumption in Korean adults.
In the present study, the risk of abnormally high TG levels was approximately two times greater in the least PA group compared to the highest PA group in both males and females. The risk of abnormal fasting glucose and HbA1c ≥5.5% were significantly higher in the least PA group compared to the highest PA group in females, but not in males. Interestingly, these findings are contradictory to previous observations [29
] demonstrating that the relative risk of abnormal postprandial glucose levels was approximately 12-fold higher in the less physically active group than the most physically active group in males, but not in females. Although further studies are required to explain these gender differences, the conflicting results may be partially explained by the difference in a heterogeneous condition (e.g., subjects without known diseases in the present study vs. subjects with T2DM) [29
]. In addition, biological or pathophysiological gender differences [30
] such as hormone levels or fat distribution may have also contributed to these conflicting results.
This study also showed that the risk of having MetS was greater in the least PA group and in those who did not meet the current PA recommendations, and that these relationships were somewhat stronger in females than in males. These results are consistent with previous observations by Vaughan et al. [8
] who reported a stronger association between PA levels and the incidence of MetS in females than in males. Previous studies have shown that females are generally less active than males [13
]. Thus, even a small increase in PA levels may result in a lower risk of MetS in females. Furthermore, compared to females, males are exposed to more habitual risk factors related to MetS (such as smoking or drinking) [31
], which may also influence the study results.
Kesaniemi et al. [33
] reported that engaging in the recommended levels of PA significantly decreases the risk of chronic health conditions. In agreement with this finding, the present study observed that Korean adults who met the current PA recommendations were more likely to have a substantially reduced risk of developing MetS than those who did not meet the recommendations. In addition, there were higher levels of abnormal metabolic parameters and incidence of MetS in males who participated in less than 9.3 MET-hr/wk and in females who participated in less than 5.5 MET-hr/wk. This suggests that a cutoff point of at least 9.3 MET-hr/wk for males and 5.5 MET-hr/wk for females may be necessary to reduce the risk of developing MetS in Koreans. In Korea, the current PA recommendations are similar to those from U.S. health organizations (e.g., ACSM), but evidence to support these PA guidelines is lacking. Additional research is needed to examine the optimal amount of PA needed to enhance health benefits for Korean adults.
The prevalence of MetS in Korea is higher than in other Asian countries [34
]. In addition, the prevalence of obesity has been increasing continuously over recent years [35
]. These changes are concomitant with decreased levels of PA and increased consumption of westernized foods [36
]. Although many Western countries have shown that increased PA reduces the risk factors associated with MetS or chronic diseases in adults [27
], this hypothesis had not been tested extensively in Korean adults. Therefore, the findings presented in this study have significant public health implications for developing effective strategies to prevent MetS, as well as for developing evidence-based PA guidelines for Korean adults in the future.
This study has several limitations. First, the IPAQ was used to determine PA levels, and subjects were divided into two categories (those who met the current PA recommendations and those who did not) using IPAQ measurement protocols. However, self-reported estimates of PA levels are known to be more prone to bias and misclassification than an objective measure such as an accelerometer [37
] Future studies should utilize more objective tools to accurately measure PA levels.
Secondly, convenience sampling was used for subject recruitment in this study, which may make the findings less applicable to the general population due to potential selection bias. In addition, given the lack of demographic data, it was not possible to control some potential confounding factors, which may have biased the study results. Further studies that control for possible confounding factors are necessary to confirm the findings of the present study. Finally, due to the cross-sectional study design, it was not possible to determine a causal relationship between PA levels and MetS or its components. Population-based longitudinal or intervention studies that include adjustments for confounding factors are necessary to explore this potentially causal relationship in Korea adults.
In conclusion, there was an inverse relationship between PA levels and MetS risk factors in Korean adults. Indeed, subjects who met the current PA guidelines had significantly lower risk of MetS than those who did not meet the recommendations. Further studies, in particular intervention studies, are needed to examine whether the current PA guidelines are sufficient for preventing MetS and enhancing the long-term health benefits for Korean adults.