Aerobic Exercise for a Duration of 90 min or Longer Per Week may Reduce the Atherogenic Index of Plasma

The correlation between the weekly duration of aerobic exercise and atherogenic index of plasma (AIP) is still unknown. A cross-sectional study was conducted involving 27,827 middle-aged Chinese men who had health examinations in our hospital. The correlation between the duration of moderate-intensity aerobic exercise and AIP was determined. The mean AIP levels were 0.1166 ± 0.34475, 0.1167 ± 0.32637, and 0.0765 ± 0.32872 in the non-exercise (PA1), occasional exercise (PA2), and frequent exercise groups (PA3), respectively. Significantly higher AIP levels were observed in the PA1 and PA2 groups than the PA3 group, while no significant difference existed between the PA1 and PA2 groups. Physical activity significantly reduced the AIP after adjustment for age, body mass index, diastolic blood pressure, and fasting blood glucose and uric acid levels. In addition, the percentage of the population at high risk for atherosclerosis (AIP ≥ 0.21) was significantly lower in the PA3 group than the PA1 and PA2 groups. Moderate-intensity aerobic exercise at a weekly duration of 90 min or longer is associated with the reduction of AIP among middle-aged men in southeastern China.

The study protocol was approved by the Ethics Review Committee of the Taihu Rehabilitation Hospital of Jiangsu Province, and the study was performed in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all participants following a detailed description of the purpose of this study.
Questionnaire survey and Measurements of cardiovascular risk factors were obtained according to the method in ref. 15 .
The atherogenic index of plasma (AIP) is defined as AIP = log 10 (TG/HDL-C) 16 . Physical activity was defined as moderate-intensity aerobic exercise, and included fast walking, running, bicycle riding, rope skipping, and swimming. All subjects were assigned to three groups (1) non-exercise group (PA1 group), no extra physical activity except daily life and work activities; (2) occasional exercise group (PA2 group), physical activity <three times a week and <30 min each session or <90 min of physical activity a week; and (3) frequent exercise group (PA3 group), physical activity >three a week and >30 min each session or >90 min a week.
AIP was also assigned to four groups according to quartile (Q1, Q2, Q3, and Q4) in each PA groups, respectively. And difference in the distribution of AIP quartiles among the each groups were compared. Risk grouping of atherosclerosis. All participants were assigned to one of three groups according to the AIP level. Subjects with an AIP < 0.11, an AIP between 0.11 and 0.21, and an AIP > 0.21 were assigned to the low-, intermediate, and high-risk atherosclerosis groups, respectively 9,17 . Statistical analysis. All measurement data are presented as the mean ± standard deviation (SD), while count data are expressed as the number (proportion). Differences in proportions were tested for statistical significance using a chi-square test, and the group comparisons were analyzed by the method of Least Significant Difference (LSD) in ANOVA. The factors affecting AIP were identified using linear regression analysis. All statistical analyses were performed using SPSS (version 16.0; SPSS, Inc., Chicago, IL, USA), with a P value <0.05 considered statistically significant.

Results
Comparison of baseline cardiovascular risk factors among groups. A total of 27,827 Chinese middle-aged men were enrolled in this study, with a mean age of 50.78 ± 6.758 years. Significant differences existed in SBP, DBP, FBP, TC, TG, HDL-C, LDL-C, UA, and AIP among the PA1, PA2, and PA3 groups; however, no significant difference was detected in the BMI among the three groups ( Table 1).
Correlation between the amount of aerobic exercise and atherosclerosis risk. The proportions of subjects at low-, intermediate-, and high-risk for atherosclerosis were 53.5%, 11.5%, and 35.0% in the PA1 group, 52.5%, 12.5%, and 34.9% in the PA2 group, and 58.0%, 11.6%, and 30.4% in the PA3 group, respectively, and there was a significant difference among the three groups (Table 3).

Discussion
There is an increase in the number of sedentary populations worldwide, which contributes to general health conditions and the prevalence of non-communicable chronic diseases. Lack of physical activity has been identified as the fourth leading cause of death worldwide 18 . Data from the China Health and Nutrition Survey (CHNS) showed a remarkable downward trend in the amount of physical activity among Chinese people between 18 and 49 years of age, and the total amount of physical activity decreased 29% and 38% in men and women in 2009, respectively, relative to 1997 19 . Considering the importance of physical activity in public health, the World Health Organization developed the "Global Recommendations on Physical Activity for Health" in 2010, with the core aim of achieving primary prevention of non-communicable chronic diseases through promotion of physical activity 18 . In 2011, the Chinese Center for Disease Control and Prevention proposed the "Guidelines on Physical Activity for Chinese Adults, " with aims to facilitate the implementation of physical activity and improve national physical quality and health level 20 , thereby resulting in the prevention and control of chronic diseases. Aerobic exercise is a type of physical activity involving large muscles for a long duration, and is widely preferred by middle-aged people. Aerobic exercise is reported to decrease fasting or postprandial TG and increase HDL-C by improving the concentration and activity of lipoprotein lipase (LPL) in skeletal muscles and accelerating lipid transfer, decomposition, and excretion 21 . Our findings showed a significantly lower TG level in the PA3 group than the PA1 and PA2 groups, and the HDL-C concentration was significantly greater in the PA3 group relative to the PA1 and PA2 groups. It has been demonstrated that 8-14 weeks of aerobic exercise leads to a decline in fasting TG level by 4-37%, and an increase in HDL-C concentration by 4-18% 22 . A weekly energy consumption ≥ 1000 kcal has been shown to decrease the TG level in men 23 , and a weekly energy consumption ≥900 kcal or >120 min of exercise a week has been reported to significantly increase HDL-C concentration, which is not affected by exercise intensity 24 . Our findings showed a significantly lower mean AIP in frequent exercisers (PA3 group) than non-exercisers (PA1 group) and occasional exercisers (PA2 group), and there was no significant difference in the mean AIP between the PA1 and PA2 groups. In addition, physical activity was shown to reduce the AIP after the adjustment of age, BMI, DBP, and FPG and UA levels.   AIP has been shown to be negatively correlated with the diameter of LDL-C particles, and has been recommended as an indirect parameter to measure the size of LDL-C particles 8 . An increase in AIP indicates a decrease in the diameter of LDL-C particles, and an increase in the proportion of small dense LDL (sdLDL) 6 . sdLDL, a subtype of LDL components that may cause atherosclerosis, has been identified as a major risk factor for coronary heart diseases and was recommended for detection by the National Cholesterol Education Program in 2002 25 . The currently available methods for detection of sdLDL have limitations, which have limited the clinical application. Therefore, AIP has superiority in the assessment of the risk for human atherosclerosis. The results of the current study showed a decreasing trend of the constituent ratio of Q1, Q2, Q3, and Q4 in the PA3 group and an increasing trend in the constituent ratio of Q1, Q2, Q3, and Q4 in the PA1 and PA2 groups; no significant difference was shown in the distribution of AIP quartiles between the PA1 and PA2 groups. In addition, the proportion of subjects at high risk for atherosclerosis was significantly lower in the PA3 group than the PA1 and PA2 groups, and the proportion of subjects at low risk for atherosclerosis was significantly higher in the PA3 group than the PA1 and PA2 groups, while no significant difference was observed between the PA1 and PA2 groups. The results demonstrated that the AIP is comparable in subjects with <90 min of physical activity weekly and non-exercisers, and a significantly higher AIP was shown in subjects with >90 min of physical activity weekly and ≥90 min of physical activity weekly. The excess post-exercise oxygen consumption of aerobic exercise may be sustained for ≥48 h 23,26,27 . In addition, the American College of Sports Medicine recommends at least 3-5 exercise sessions per week, and the health benefit from 1-2 exercise sessions per week was less than 3-5 exercise sessions per week; however, comparable health benefits existed between subjects engaged in exercise daily and subjects exercising five times per week. The study subjects enrolled in this study were middle-aged Chinese men whose living conditions, dietary habits and constitution differ from Western populations. Our findings indicate that moderate-intensity aerobic exercise ≥ three times per week and an accumulated duration ≥90 min a week may achieve substantial benefits with respect to cardiovascular health.
Limitations. The amount of physical activity was calculated using the duration of activity, which was not transformed to energy consumption. In addition, the study subjects recruited in this study were middle-aged Chinese men. Therefore, region-, race-, gender-, and age-specific variations should be taken into account if the conclusions drawn from this study are used.

Conclusions
Physical activity has multiple health benefits, including weight loss, lowering of blood pressure, and improvement in blood lipid and glucose levels. The AHA highlights the significance of physical activity in terms of cardiovascular health. Our findings showed that weekly moderate-intensity aerobic exercise ≥90 min significantly might decrease the AIP and other cardiovascular risk factors in middle-aged men. Given that a lack of physical activity is a major risk factor for cardiovascular diseases in China, physical activity-based health promotion may be a low-cost, highly-effective strategy for the promotion, prevention, and control of cardiovascular health.