The Effects of a Short-term Aerobic Training on Biochemical Cardiovascular Risk Factors and IL-6 in Obese Females

Introduction: Obesity participates in the progression of systemic inflammation and cardiovascular disorders. We aimed to assess the impacts of aerobic training on serum interleukin-6 (IL-6) and risk factors for cardiovascular dysfunction in obese women. Methods: Physically inactive, obese women matched for age (38 ± 5 years) and body mass index (BMI) (30 ≤BMI ≤36 kg/m2) were randomly divided into exercise (moderate aerobic training, 6 weeks, 3 d/wk, n = 13) and control (no training, n = 13) groups. Preand post-training measurements of anthropometric markers, serum IL-6 and cardiovascular risk factors were done. Within and between groups comparisons were performed by paired sample t-test and independent sample t test, respectively. Results: Aerobic training induced significant decreases in body weight, BMI, body fat (%) and abdominal obesity as anthropometric markers (P < 0.05). Compared to pre-training condition, serum IL-6, triglyceride (TG), total cholesterol (TC) and Low-density lipoprotein cholesterol (LDL-C) showed no alterations by aerobic training in the exercise group (P > 0.05). However, participants in the aerobic training group revealed a significant increase in high-density lipoprotein cholesterol (HDL-C) and a decrease in TG/HDL and LDL/HDL (P < 0.05). Conclusion: Short-time aerobic training does not appear to contribute to circulating serum levels of IL-6 in obese females; however, it affects lipid profile and may be considered as a beneficial non-pharmaceutical intervention against cardiovascular diseases in obese women.

to microbes and other cytokines. 6It has been found that high plasma IL-6 concentrations are accompanied by a reduction in muscular mass and function. 7ome recent studies stated that circulating levels of inflammatory cytokines such as IL-6 varies depending on the amount of adipose tissue. 8It is believed that weight loss, especially in obese people, is accompanied by improved inflammatory and metabolic profiles.In this regard, some studies have reported that inflammatory profile improves following short-and long-term training programs.In a recent study, 12 aerobic/resistance training resulted in a significant decrease in serum tumor necrosis factor-alpha (TNF-α) and IL-6 in middle-aged obese men. 9 In another report, 1-year weight loss program was accompanied by improved cardiovascular risk factors. 10evertheless, 6-month aerobic training program did not result in any changes in proinflammatory cytokines such as IL-6, C-reactive protein (CRP), and TNF-α in obese or overweight postmenopausal women. 11In another study, a 12-week aerobic training program did not cause any changes in the levels of cardiovascular risk factors such as cholesterol, triglyceride, and HDL in obese women with metabolic syndrome. 12However, inflammatory mediators such as IL-6 improved following 16-weeks aerobic training and respiratory muscle training program. 13,14 limited number of studies have focused on the importance of aerobic exercise in modulating levels of IL-6 and cardiovascular markers in obese women.Based on this contradiction, this study attempted to assess the impacts of a 6-week aerobic training on serum levels of IL-6 as an inflammatory cytokine and cardiovascular risk factors in sedentary obese women.

Study Subjects
Participants of this semi-experimental study included 26 sedentary obese pre-menopausal women matched for age (38 ± 5 years) and body mass index (BMI) (32 ± 3 kg/m 2 ) that participated by convenience sampling.The subjects were randomly allocated into aerobic training (n = 13) or control (n = 13) groups.

Inclusion and Exclusion Criteria
Inclusion criteria for subjects were: being healthy, being middle-aged, and having obesity (30 ≤ BMI ≤36).Participants were non-alcoholics, non-athletes (VO2max ≤27 mL/kg/min) and non-smokers.Participants did not participate in any regular physical activity or follow any specific diet within the past 6 months.The exclusion criteria included a history of diabetes, acute or chronic respiratory infections, cardiopulmonary and neuromuscular disease.Anthropometry Anthropometric indexes were measured for each subject.Obesity was determined by BMI (kg) divided by height squared (m 2 ).The height and weight were measured by the same person for each subject.The height and weight measurements were carried out with the least amount of clothes on with no shoes.Abdominal and hip circumference and the ratio between them (AHO) were documented in standing position.Body composition monitor (OMRON, Finland) used to measure body fat (%).

Exercise Program
Aerobic training was performed for 6 weeks, 3 sessions per week.The protocol included warming up (10 minutes), and then 30 to 45 minutes of the main exercise at 60 to 70% of maximum heart rate followed by a coolingdown period. 15The training activity included walking or running on a treadmill without slope.Moreover, subjects in the exercise group were advised to do regular physical activities such as brisk walking and so on.The exercise intensity was up to 60% of maximum heart rate in the first week and then was gradually increased during the study period.For each subject, exercise intensity decreased by 5% during menstrual cycles. 16Control subjects were asked to continue their daily routine activities.Participants were also requested to follow their usual diet.

Biochemical Analysis and Assay
Blood samples were taken from each subject considering a 12-hour overnight fasting period.They were requested to avoid vigorous physical activity 48 hours before sampling.Post-training blood samples were collected 48 hours after the last exercise session.Serums were separated and stored at -80°C until use.Serums were used to measure IL-6 and biochemical cardiovascular risk factors.ELISA method was used for determining serum IL-6 (Biovendor-Laboratorial kit made by Biovendor Company, Czech).Coefficients of variation (CV) of the kit were 3.4% (intraassay) and 5.2% (inter-assay), respectively.TG, TC, HDL and LDL cholesterol were measured using the colorimetric enzymatic method (Pars Azmoon, Tehran, Iran).

Data Analysis
Data was analyzed using SPSS statistical software package version 16.0 (SPSS Inc., IL, USA).Normal distribution was checked by Kolmogorov-Smirnov test.Comparisons of each variable between the 2 groups were done using independent sample t test.Comparisons between pre and post-training measures were done by paired sample t test.A P value of less than 0.05 was considered statistically significant.

Results
Table 1 shows the anthropometric features at the pre and post-training time points.All values have been reported as mean and standard deviation (SD).Based on the results of independent sample t test, no statistically significant differences were found between the 2 studied groups at baseline (P > 0.05).On the other hand, aerobic intervention induced a significant decrease in body weight, BMI, abdominal obesity and body fat (%) in exercise groups but these variables remained unchanged in control subjects (P < 0.05; Table 1).At baseline (pre-training), serum IL-6 levels were not different between the two groups (P = 0.423).Despite the reduction in anthropometric indexes, no significant alteration was noticed in serum IL-6 level after aerobic intervention compared to pre-training levels in the aerobic exercise group (P = 0.092).There were no differences in the cardiovascular risk factors between the 2 groups at baseline (P > 0.05).No differences in TC, TG and LDL cholesterol were found after aerobic training compared to their respective baseline values in the exercise groups (P > 0.05).In contrast, HDL cholesterol was significantly increased by aerobic training in the exercise group (P = 0.022) but not in control subjects (P = 0.723).In addition, compared to pre-training, TG/HDL (P = 0.011) and LDL/HDL (P = 0.009) decreased significantly in exercise subjects, but not in the control subjects (P > 0.05) (Table 2 and Figure 1).

Discussion
We found that levels of IL-6, which is an inflammatory cytokine, did not change following 6 weeks of aerobic training in obese women.Although the training intervention was associated with a decline in serum IL-6, this reduction was not statistically significant; however, these changes were remarkable from a clinical perspective.Moreover, this program was not accompanied by any changes in the levels of TG, TC, and LDL as cardiovascular risk factors, although serum levels of HDL significantly declined.Most studies support higher levels of inflammatory cytokines in the presence of obesity. 17he role of inflammatory markers in the etiology of diabetes has been proposed as well as the potential effects of IL-6 and CRP in determining markers of metabolic syndrome and type 2. 1 IL-6 as an active inflammatory cytokine is produced by many cells such as leukocytes, adipocytes, and endothelial cells. 18Researchers believe that IL-6 is related to hyperglycemia, insulin resistance, and type 2 diabetes as a critical physiological marker sensitive to systemic inflammation. 1This inflammatory marker has also been introduced as a predictor of cardiovascular diseases. 19Injection of IL-6 to healthy people or patients with type 2 diabetes increases lipolysis without inducing the elevation of triglyceride or changes in catecholamines, glucagon, and insulin. 20Suppression of IL-6 under clinical conditions leads to increased cholesterol and higher glucose levels. 21Moreover, several studies mentioned that IL-6 can be involved in the oxidation of free fatty acids in intracellular spaces and in the whole body. 20Similar to inflammatory profile, higher levels of blood lipids have been reported in obese people. 22The researchers believe that weight loss or reduction of body fat is associated with the improvement of cardiovascular risk factors in obese populations. 22For example, in one study, a weight loss of 11 kilograms led to improved levels of LDL and TC as cardiovascular risk factors. 10Improved lipid profile markers following aerobic training have also been reported by some other studies. 23Nevertheless, there are studies reporting that cardiovascular risk factors did not change following short or long-term training programs in obese populations. 24he response of inflammatory cytokines to exercise or diet interventions in healthy or sick populations is often contradictory.Although the main mechanisms responsible for this paradox have not been completely known yet, this contradiction can be somehow attributed to the training program in terms of duration, frequency, and volume of exercise, measurement tools, and the study population.In the present study, the short-term training program may have been one of the factors responsible for the lack of improvement in IL-6 or cardiovascular risk factors.Despite the significant weight loss observed in response to the 6-week aerobic training in this study, some studies have considered a minimum of 10% reduction in body weight in response to training programs as a sufficient condition for improvements in inflammatory cytokines or cardiovascular risk factors in obese populations. 25owever, in one study, a short-term (4 weeks) training led to the reduction of cardiovascular risk factors along with the increase in HDL. 26 Moreover, some studies have not reported a reduction in body weight or body fat percentage.In one of these studies, despite the lack of changes in BMI or body fat percentage, the researchers reported a significant reduction in inflammatory cytokines in the elderly. 27lder people, regardless of the type of disease, suffer systemic inflammation, and numerous studies have indicated a link between physical activity and inflammatory mediators in this population. 28Therefore, it is believed that higher levels of inflammation in old people is an appropriate explanation for the greater response of the inflammatory profile in them in response to exercise training, even in the absence of the change in weight or body fat.Accordingly, it is assumed that, apart from variations in weight and body fat, the gradual increase of age is effective in the improvement of the inflammatory profile in response to exercise trainings.
In other studies, a significant inverse relationship has been confirmed between the physical activity level and inflammation in young men and women. 29Some researchers also stated that the beneficial effects of exercises were not tangible without dieting. 30The researchers also believe that diet control or having a proper diet when performing exercise trainings, particularly in healthy or sick obese individuals, severely affects the inflammatory profile. 31Despite this evidence, in the study by Gueugnon et al, a 9-month program consisting of dieting and aerobic training did not significantly change serum resistin levels. 32Moreover, despite the lack of changes and without any diet control in a recent study, the 24-week combined training (aerobic-resistance) improved the mediators of inflammation (adiponectin, leptin, resistin, and CRP) and insulin resistance in obese men, 33 although serum IL-6 and IL-10 did not change.Some of these researchers attributed the improvement in inflammatory profile to increased cardiovascular fitness resulting from training programs. 34,35In this relation, the findings of a study indicated increased levels of VO2max in response to 3 and 6 months of intensive aerobic and resistance training which led to significant improvement in cardiovascular risk factors and reduction in the inflammatory markers. 36In another study, a significant relationship was found between inflammatory profile, aerobic fitness, and muscular fitness of Norwegian children. 37However, some studies on healthy young and middle-aged men or women have not reported any significant correlation between the physical activity level and any inflammatory cytokines such as CRP, IL-6, and TNF-α receptors 1 and 2, even after adjusting for BMI. 38

Limitation
We did not measure VO2max and other inflammatory cytokines in response to the training program that is considered as a limitation of our study.

Conclusion
Despite the fact that 6 weeks of aerobic training induced a significant increase in HDL in obese women, no changes were detected in other lipid indicators and IL-6.This may be due to the short duration of training.The optimal effects of this training program are important from a clinical perspective, emphasizing a significant increase in HDL and a reduction in TG/HDL and LDL/HDL.

Competing Interests
The authors declare that they have no competing interests.

Ethical Approval
Our study was approved by the Ethics Committee of the Islamic Azad University, Iran, and a written informed consent obtained from participants.

Table 1 .
Comparison of Descriptive Anthropometric Features Before and After the Aerobic Intervention in Exercise and Control Groups

Table 2 .
Comparison of Serum IL-6 and Cardiovascular Risk factors Before and After the Aerobic Intervention in Exercise and Control Groups Abbreviations: TC, total cholesterol; TG, triglyceride; LDL, low density lipoprotein; HDL, high density lipoprotein.