Effects of aerobic exercise on cholesterol in children and adolescents
In this work, the authors used the meta-analysis technique to evaluate the effectiveness of aerobic exercise in reducing the levels of non-HDL cholesterol in children and adolescents.
Introduction
It has been suggested that minimal increases in lipid and lipoprotein levels in children and adolescents may increase the risks of cardiovascular disease in adulthood. This is not a minor fact, since cardiovascular disease is the leading cause of death in adults in the United States with approximately 696,947 deaths per year.
Aerobic exercise is a healthy, accessible, non-pharmacological practice that is usually indicated in children and adolescents for the treatment of most lipid disorders. The main objective is the decrease in the level of low density cholesterol, however the non-high density cholesterol (non-high-density lipoprotein cholesterol, non-HDL cholesterol) is a better predictor of cardiovascular disease, its calculation is performed in based on total cholesterol minus high density cholesterol.
In this work, the authors used the meta-analysis technique to evaluate the effectiveness of aerobic exercise in reducing the levels of non-HDL cholesterol in children and adolescents.
Method
For the search the authors included works done in the last 52 years (1955-2007), included in 5 electronic databases (PubMed, EMBASE, Sport Discus, Cochrane Central Register of Controlled Trials, Dissertation Abstracts International). For inclusion, the works should be published in English, be randomized and controlled, range of age children to adolescents up to 19 years, with at least 4 weeks of aerobic exercise, without dietary or pharmacological intervention, and that have been measured, or at less could be calculated non-HDL cholesterol.
Each of the articles was evaluated independently by each of the authors.
The primary outcome measure was the change in the concentration of non-HDL cholesterol, other outcome measures studied secondarily were total cholesterol, high-density cholesterol, and body weight.
To calculate the variance of the therapeutic effect for each outcome measure, the sharing of the changes in the dispersion of the score of each group (aerobic exercise / controls) was used.
The 95% confidence intervals (95% CI) were considered, the Q index of heterogeneity was calculated, and an index ≤ 0.10 was considered positive.
Publication biases were also studied by the Egger regression. Finally, the authors used a meta - regression to evaluate the relationship between changes in non - HDL cholesterol and initial levels of total cholesterol; non-HDL cholesterol, age, changes in weight, duration and frequency of aerobic activity, quality of the study and year of publication.
In all the works, the quality of the study was observed and calculated.
Results
Characteristics of the study
Out of a total of 235 studies reviewed, 14 met the inclusion criteria. However, there were 2 works in which the outcome measures were evaluated but without reporting the data in full, leaving a total of 12 works included and evaluated. All corresponded to controlled and randomized studies. Of these, 9 studies were conducted in the United States, 2 in Greece and 1 in the United Kingdom. They corresponded to 25 groups of patients (13 exercise and 12 control groups), representing a total sample of 404 participants (221 exercise and 183 controls). In all the studies, analysis by protocol of the data was performed. In the exercise group there were 0-28% of patients not evaluable and in the control group of 0-20%. The quality of the works that participated had a median of 2 points in the quality score.
Characteristics of the participants
There were 5 studies that included only men in the sample, 1 only women and the 6 remaining included both sexes. Regarding the use of medication, 5 studies clarified that the participants did not take any type of medication. In 8 of the 12 studies it was clarified that none of the participants participated in any training program. In addition, 8 studies reported on the diet of the participants, ensuring that it was not modified during the study.
Characteristics of lipid evaluation
The lipid evaluation was carried out during the morning with a previous fast of 8 to 12 hours. Physical activity was also avoided in the 24 to 72 hours before the extraction.
Characteristics of the training program
Only 5 of the 12 studies adequately reported the training program and adherence to it. All exercise sessions were supervised. The activities consisted of ergometric cycles, walks, jogging, and aerobic dances.
Results
General results
Through the designs and categories, a slight decrease of 0.6% of non-HDL cholesterol was observed in the study group vs. the control group, difference not significant.
There was great heterogeneity among the groups studied, however the analysis did not show significant publication biases.
In the same way as it happened with the non-HDL cholesterol, no significant changes were found in terms of total cholesterol and HDL cholesterol. However, if there was a decrease in body weight and an increase in aerobic capacity, in the study group (exercise), both results were statistically significant.
Sensitivity analysis of non-HDL cholesterol
No significant difference was found in the levels of non - HDL cholesterol in both groups (study and control). In addition, the cumulative meta - analysis for years shows that there were no significant changes since 1983. No statistically significant differences were found in any of the sensitivity analyzes conducted, including meta - regression analysis.
Discussion
The primary objective of the present work was to use the meta - analysis technique to have an approximation to the evaluation of the effects of physical exercise on the levels of non - HDL cholesterol in children and adolescents.
According to the authors, in general terms, physical exercise is not effective to reduce levels of non-HDL cholesterol. These results contrast with a previous meta - analysis that showed a 4% decrease (statistically significant) after incorporating walks in adult patients.
The authors describe the impossibility to identify any cause with statistical significance for the heterogeneity of non - HDL cholesterol results. One of the possible causes could have been the lack of registration of variables that may be related to this dispersion of values.
Another possible reason for the lack of statistically significant results was the adopted criterion, which included a confidence interval of 99% for the variables under study. A very rigorous criterion where the "zero" can be easily understood, the differences being without statistical significance.
Regarding the secondary results, 7% showed a decrease in weight. This data suggests that aerobic exercise could be beneficial for weight loss. Important fact if one takes into account the high incidence of obesity in children and adolescents. The CDC (Center for Disease Control) recommends for all children the performance of aerobic exercise of at least 60 minutes at a moderate intensity for most of the days of the week, preferably daily. These types of exercises include fast walks, cycling and swimming.
Meta - analysis, like any other type of review, has its limitations. The authors note that only two studies included overweight patients. Likewise, the data referred to some variables were not always consistent or complete. This caused the impossibility of performing any type of multiple regression analysis, a common fact in this type of research.
conclusion
The results presented suggest that physical exercise does not significantly lower non-HDL cholesterol. If instead it decreases body fat and increases aerobic capacity in children and adolescents.
More controlled and randomized studies focused on children and adolescents with high levels of lipids and lipoproteins are needed.
Commentary
In certain cases, when a large-scale study is not available, the meta-analysis is a valid resource, although its results must be considered in their context and always take into account the possibility of biases related to the interpretation of the results and with the selection of the works. In any case to evaluate the effectiveness of a treatment (as in this case, exercise) the best model is the double blind randomized controlled study. Probably hard to perform.
Something is clear, this work can not rule out the usefulness of physical exercise to lower non - HDL cholesterol. Therefore, more studies will be needed in this regard and there would be no reason not to advise healthy physical activity in our patients.
Something is clear, this work can not rule out the usefulness of physical exercise to lower non - HDL cholesterol. Therefore, more studies will be needed in this regard and there would be no reason not to advise healthy physical activity in our patients.
Regarding the discussion, the authors propose a preliminary meta - analysis in adults who with walking achieved statistically significant results. Perhaps a possible explanation could be the difference in habitual physical activity in both age groups. Children and adolescents usually perform physical activity, unlike most adults. Therefore, intervention in children and adolescents does not increase physical activity enough to lower cholesterol levels, unlike what can happen in adults.
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