The Relationship Between Body Mass Index, Waist Circumference And Quality Of Life: The Regulatory Effect Of Exercise

Objective and purpose:Nowadays,overweight and obesity have become a global public health problem,and most researchers believed that obesity was a risk factor for many chronic diseases and can reduce the quality of life.In recent years,however,studies on the relationship between overweight,obesity and health have suggested that overweight and obesity took a lower risk of death and a better survival prognosis and did not diminish the quality of life,especially in the mental component summary.This phenomenon,which was contrary to the results of previous research,was called the "obesity paradox".With the increase of related reports,the possible mechanism of obesity paradox has been explored and discussed extensively.Most studies had shown that exercise played an important role in improving human function,reducing weight,relieving stress,and promoting physical and mental health.Scientific exercise was also an effective means of reducing fat and shaping the perfect body.In addition,exercise was associated with health and body mass index(BMI)and waist circumference(WC).At present,it has been confirmed that BMI,WC,exercise and quality of life(QOL)were related to each other,but the relationship among them was not clear.As an important method to explore the mechanism of the third factor,moderating effect has been widely used in sociology,psychology and other related disciplines.Is there a moderating effect between BMI,WC and QOL,If there is a moderating effect,is this effect the cause of the phenomenon of"obesity paradox"to some extent?This series of problems are not clear.This study intended to establish a model of"BMI,WC-exercise-QOL",aiming to explore the mediating effect of exercise between BMI,WC and QOL,explore the possible mechanism of"obesity paradox",and understand the role the movement played in the health of different body types.It could help people to form correct sports and health concepts,thereby improving the quality of life and improving health level.Methods:A total of 1554 subjects were selected from the database of "Systematic investigation of physiological parameters of pulse diagnosis of different physique of normal population".The general information(age,sex,marital status,the education level),physical indexes(height,weight,waist circumference),daily habit(smoking habit,drinking habit and exercise habit(weekly exercise times,time per exercise)),past history of disease and the Medical Outcomes Study 36-Item Short-Form Health Survey(SF-36)(SF-36)were included in the analysis.Body mass index(BMI)was calculated from height and weight(BMI=weight/height2(kg/m2).18.5,24 and 28 were taken as critical values and the subjects were divided into four groups:lightweight,normal weight,overweight and obesity.The classification criteria of waist circumference(WC)was as follows:85cm<WC<95cm for males,80 cm<WC<90cm for females are diagnosed as central obesity,WC?95cm for males and WC?90cm for females are diagnosed as severe central obesity.The SF-36 scale could evaluate the physical health status of the subjects from the domain of physical component summary(PCS)and its dimensions of physical function(PF),role-physical(RP),physical pain(BP)and general health(GH).Mental component summary(MCS)and its dimensions of vitality(VT),social functioning(SF),role-emotional(RE)and mental health(MH)could evaluate the psychological state of subjects.The specific statistical analysis methods were as follows:1.X2 test was used to analyze the BMI,WC typing characteristics of the sample population;2.ANOVA was used to compare the difference of QOL in different groups of BMI and WC.The normal weight group and non-central obesity group were taken as the reference groups,and Dunette method was used to compare the differences between groups.3.The influence of BMI,WC and confounding factors on QOL was studied by the regression analysis.4.The amount of exercise per week was calculated from "weekly exercise times*per times of exercise".420 cases(27.0%)with the highest numerical value and 420 cases(27.0%)with the lowest numerical value were categorized to the group of the high level of exercise and low level of exercise respectively.A grouping regression was used to analyze the moderating effect of exercise on BMI,WC and quality of life.The specific values of BMI,WC indices were standardized as independent variables(the value of each sample minus the mean value of the samples in its group).The exercise level(moderator variable)was treated as a dummy variable(the group of low level was treated as the reference group=(0,0),and the high level group=(1,0)).The interaction terms of"BMI*exercise level"and "WCa*exercise level"were generated.Incorporate control variables(age,educational level,previous medical history,etc.),standardized independent variables,virtualized moderator variables and interaction items into the regression model.If the regression coefficient of the interaction term was significant,there was a moderating effect.To further explain the relationship between Y and X,respectively in different groups of exercise level,two values that one was lower than the average and standard deviation of the independent variables(X=0-1 SD)and the other was higher than the average and standard deviation(X = 0+1 SD)were included in regression equation.According to the four numerical values,adjustment effect diagram could be made.How the exercise affected the direction and size of the relationship between BMI,WC and QOL was judged according to the moderating effect diagram.Results:1.Characteristics of respondents with BMI,WC type:In the crowd of males,45-65-year-old people,married,low-educated,having a previous medical history and having a preference of smoking,drinking and exercise were more likely to be overweight and obese.2.QOL of respondents with BMI,WC type:In the physical component summary,comparing with the normal group,there was no significant difference between the overweight group and the normal group(P>0.05).The scores of PCS,PF and GH in obese group were lower,and the scores of PCS,RP and GH in underweight group were lower.There were no significant differences in the scores of PCS,RP,BP and GH among different types of WC in physical component summary(P>0.05).In mental component summary,comparing with the normal group,the scores of MCS.,SF and RE in the underweight group were lower.In MCS,VT and RE,the scores in the overweight group were significantly higher than those in the normal group.There were no significant differences between obese group and normal group in MCS and its dimensions.The scores of central obesity in MCS and dimensions of VT,RE and MH were significantly higher than those in the group of non-central obesity,and the score of RE in the group of severe central obesity was significantly higher than that in the group of non-central obesity.3.The influence of BMI,WC on QOL:In physical component summary,there was a negative influence of BMI on the dimensions of BP and GH.And there was a negative influence of WC on PF.In mental component summary,BMI and WC both affected the dimension of SF positively.Among the confounding factors,gender and weekly exercise significantly affected the two domains and most of dimensions.Males and high level of exercise affected QOL positively.4.The scores of QOL in the group of high level of exercise were higher than those in the group of the low level.5.The moderating effect of exercise between BMI,WC and QOL:There were moderating effects between BMI and PCS and the dimensions of BP,GH.And there were moderating effects between WC and the dimensions of BP,GH.When the level of exercise was low(M=0),BMI and WC index could positively predict QOL.When the level of exercise was high,BMI and WC index negatively predicted the QOL.There were moderating effects of exercise between BMI and PCS,BP,GH among males,and between WC and PCS,BP,which were consistent with the analysis of the moderating effect of exercise in the total population(a sample of 840 cases).In addition,there were moderating effects of exercise between BMI and MCS,SF among males,and between WC and SF.The moderating effect only consisted in the dimension of GH among females.Conclusions:Compared with normal weight,the quality of life of overweight and obese group had no significant difference in physical component summary(PCS),especially better in the mental component summary(MCS).Quality of life(QOL)of the group of the high level of exercise was better than that of the group with low level.The relationships between BMI,WC and QOL were affected by different levels of exercise.When the level of exercise was low,QOL would increase with the increase of BMI and WC index.When the level of exercise was high,QOL would decrease with the increase of BMI and WC index.This might explain the mechanism of the "obesity paradox"to a certain extent,and also provided a basis for us to understand the role of exercise in the health status of people of different body types.In addition,it could help us form correct health concepts and improve our QOL.