| The prevalence of obesity is increasing at an alarming rate in many parts of the world.About 2 billion people are overweight and one third of them obese.Over the last three to four decades,overnutrition and obesity have been transformed from relatively minor public health issues that primarily affected the most affluent societies to a major threat to public health that is being increasingly seen throughout the world.The plight of the most affected populations,like those in high-income countries in North America,Australasia and Europe,has been well publicized.However,the more recent increases in population obesity in low-and middle-income countries that are now increasingly being observed have been less recognized.The Global Burden of Metabolic Risk Factors of Chronic Diseases Collaborating Group analyzed data from 199 countries and territories and 9.1 million adults with respect to the prevalence of overweight and obesity between 1980 and 2008.During that 28-year period,the prevalence of obesity nearly doubled worldwide.In 2008,about 1.5 billion adults were estimated to have a body mass index(BMI)of 25 or more(about 34%).Of these,500 million were considered obese(about 10% in men and 14% in women).More recently,the analyses for the Global Burden of Disease Study 2013 further documented that worldwide,the proportion of adults with a BMI of 25 or greater increased between 1980 and 2013 from about 29 to 37% in men and from about 30 to 38% in women.These estimates are slightly higher than those calculated during 1980-2008,which reflect further increases between 2008 and 2013,but this may also be due to methodological differences between the two studies.Since 2006,the increase in adult obesity seems to have leveled off in several high-income countries,but the incidence generally remains higher than in most low-and middle-income countries.The epidemiology of obesity has for many years been difficult to study because many countries had their own specific criteria for the classification of different degrees of overweight.Gradually,during the 1990 s,however,the BMI(weight/height2)became a universally accepted measure of the degree of overweight,and now,identical cutoff points are generally recommended.Based on WHO recommendations,normal weight was defined as BMI <25.0,and general obesity was defined as BMI ?30.0 for adults aged ?20 years.According to the criteria of the Working Group on Obesity in China(WGOC),general obesity was defined as BMI ?28.0 and normal weight was defined as BMI <24.0.Obesity causes or exacerbates many health problems,both independently and in association with other diseases.In particular,it is associated with the development of type 2 diabetes mellitus,coronary heart disease(CHD),an increased incidence of certain forms of cancer,respiratory complications(obstructive sleep apnoea)and osteoarthritis of large and small joints.The Build and Blood Pressure Study has shown that the adverse effects of excess weight tend to be delayed,sometimes for ten years or longer.Life-insurance data and epidemiological studies confirm that increasing degrees of overweight and obesity are important predictors of decreased longevity.In the Framingham Heart Study,the risk of death within 26 years increased by 1% for each extra pound(0.45 kg)increase in weight between the ages of 30 years and 42 years,and by 2% between the ages of 50 years and 62 years.However,a recent meta-analysis conducted by Flegal et al.,which included 97 studies with a combined sample size of 2.88 million and more than 270,000 deaths,found that overweight was associated with a decreased risk of mortality relative to normal weight(hazard ratio(HR)=0.94,95% confidence interval(CI): 0.91-0.96).The discrepancy in results may reflect the differences in age distribution,BMI distribution,reference BMI category used,preexisting chronic disease,and potential confounding factors.Currently,the relationship between overweight and all-cause mortality remains controversial.Most findings concerning obesity in the risk of all-cause are generally based on analyzing only the level of body mass index(BMI).Studies have demonstrated the importance of taking into account the potential cumulative effect of the duration of obesity,rather than the simple assessment of obesity at a single point in time(eg,at baseline).Duration of obesity has been shown to be a risk factor for mortality,CVD and type-2 diabetes independent of BMI.Nevertheless,analyses based on either level of BMI alone or duration lived with obesity alone,may not reflect the total effect of obesity and may underestimate the risk of death attributable to obesity.Recently,studies demonstrated the additional benefit of combining the level of obesity with the number of years lived with obesity into a single measure,finding that an Obesity-Years metric is a better predictor of the risk of type-2 diabetes,cardiovascular disease and cancer than level of BMI or duration of obesity alone.With the increasing global pandemic of obesity,there has also been a dramatic rise in the number of obese adults in China.For example,during 1989–2000,the prevalence of obesity combined with overweight increased by 50% in adults aged 20-45 years.However,most previous estimates of obesity and overweight were either based on limited survey data that only reflected a relatively short period of changes in obesity or on clinical data.Recent prevalence and trends in the distribution of BMI among Chinese adults remain unknown.Most of these previous studies have been conducted in Western populations in which a high proportion of participants are obese.It is still unclear whether the findings of these studies can be extrapolated to Asia populations.Although Gu et al.reported a U-curve relationship between BMI and all-cause mortality in the Chinese adult,the study included only adults age ?40 years but not adults aged 20 years or older.It has been proved that Obesity-Years metric is a better predictor for risk of CVD,diabetes and cancer than current BMI or duration of obesity alone.However,whether this metric is a better predictor for risk of death is unknown.In the part one,the study aims to estimate the current prevalence of obesity and to assess trends in obesity and BMI distribution in Chinese adults from 1991 through 2011.Part two aims to evaluate the association between body mass index and the risk of all-cause mortality.Part three aims to analyze the association between the duration together with degree of obesity/overweight and the risk of all-cause mortality,and to explore whether the Obesity-Years and Overweight-Years are better indicator for the risk of death.Part one: Prevalence and Secular Trends in Obesity and verweight Among Chinese Adults,1991-2011Objectives:The prevalence of obesity in Chinese adults increased from 1991 to 2000;however,recent changes in this trend are unclear.This study aims to estimate the current prevalence of obesity and to assess trends in obesity and BMI distribution in Chinese adults from 1991 through 2011.Methods:This study was based on data from eight waves of the CHNS conducted from 1991-2011 and focused on adults aged ?20 years.To limit biases caused by pre-existing factors,this analysis excluded participants who had been diagnosed with pregnancy or were lactating.In addition,participants with missing information on height or weight or extreme or implausible height(<120.0 cm)or BMI(<15.0 or >40.0)values were also excluded.The age and sex specific prevalence of overweight and obesity were calculated based on the criteria of the Working Group on Obesity in China(WGOC)and WHO recommendations.The chi-square test was applied to analyze the differences in the prevalence of obesity between men and women as well as differences between the Chinese and the U.S.population.Trends in the prevalence of obesity and of overweight and obesity combined among participants from 1991 to 2011 were assessed by linear-by-linear trend testing.Logistic regression was utilized to further assess the annual changes in obesity throughout the eight waves of the CHNS,as well as the differential increase rate by sex with an interaction term(sex *survey time).Linear regression was applied to assess the trends in BMI.To further examine trends in BMI,selected percentiles were graphed.Results:Based on the exclusion criteria,the remaining participants aged ?20 years were 8,142 for 1991;7,776 for 1993;8,282 for 1997;9,184 for 2000;8,966 for 2004;8,982 for 2006;9,297 for 2009;and 12,249 for 2011.In the 2011 survey,the age-adjusted mean BMI was 23.8(95% CI=23.7,23.9)for men and 23.4(95% CI=23.2,23.5)for women.The age-adjusted prevalence of obesity was 11.3%(95% CI=10.8%,11.9%)overall,11.8%(95% CI=10.8%,12.6%)among men,and 11.0%(95% CI=10.3%,11.8%)among women.The overall age-adjusted prevalence of overweight and obesity combined was 42.3%(95% CI=41.3%,43.4%),46.1%(95% CI=44.5%,47.7%)among men and 39.3%(95% CI=37.9%,40.6%)among women.Estimates of age-adjusted obesity prevalence among the Chinese population were significantly lower than those of the U.S.population(all P<0.05).Over the 20-year period,the prevalence of obesity increased from 2.88% to 11.8% among men(age-adjusted annual change in OR=1.08,95% CI=1.07,1.09,P <0.001)and from 4.55% to 11.0% among women(OR=1.05,95% CI=1.05,1.06,P <0.001).Similar significant findings were observed for both men and women based on WHO recommendations.Conclusions:In 2011,the prevalence of obesity is11.3% and the combined prevalence of overweight and obesity is 42.3%,which is 3.27 times and 2.84 times of that in 1991.The prevalence of overweight and obesity is different in population born in different periods.The odds ratio of obesity in Chinese adults is 0.32 times higher than that in the United States,and the combined prevalence of overweight and obesity is 0.45 times higher than that in the United States.Part two: Association between Body mass index and the risk of ll-cause mortality in a prospective cohort of Chinese dultsObjectives:Obesity is associated with an increased risk of diabetes mellitus,hypertension,and coronary artery disease;however,the relation between obesity and death is controversial.This study aims to evaluate the association between body mass index(BMI)and the risk of all-cause mortality.Methods:Participants aged ?18y from the survey of the China Health and Nutrition Survey from 1989 to 2009 with BMI information together with survival status were included.To limit biases caused by pre-existing factors,this analysis excluded participants who had been diagnosed with pregnancy or were lactating.In addition,participants with missing information on height or weight or extreme or implausible height(<120.0 cm)or BMI(<15.0 or >40.0)values were also excluded.Based on the criteria of the Working Group on Obesity in China(WGOC),BMI were divided into 4 categories: BMI <18.5,18.5? BMI <24.0,24.0 ? BMI ?28.0 and BMI ?28 kg/m2,and that is underweight,normal weight,overweight and obesity,respectively,and the allcause mortality rate in each categories were calculated based on the basic BMI.In addition,the those participants were also divided into always underweight,normal weight or ever underweight,ever overweight and ever obesity groups,and corresponding all-cause mortality rates were calculated.The all-cause mortality rate were adjusted by direct method for the 2010 census of the Chinese adult population using the corresponding age groups.Cox proportional hazard models were applied to determine the all-cause mortality risk associated with basic BMI and dynamic BMI adjusted for potential confounders.Results:Based on the exclusion criteria,there are 17,295 participants were included in this study(8,109 were men;9,186 were women).During a mean follow-up period of 15.2 years,there are 1,311 deaths,and the age-adjusted mortality rate was 723.5(95% CI=642.6,837.1)/105 person-year.According to the basic BMI,The Hazard Ratios(HRs)in underweight,overweight and obesity were 1.53(95% CI=1.31,1.78),0.84(95% CI=0.72,0.98)and 0.92(95% CI=0.72,1.18)respectively.The associations in men were in accordance with overall,while no protective effect was observed in the overweight participants of women,overweight participants from urban or rural regions,overweight participants with any smoking status or drinking status.Based on the dynamic BMI,comapred with the normal weight or ever underweight participants,HRs in always underweight,ever overweight and ever obesity were 1.71(95% CI=1.42,2.07),0.67(95% CI=0.59,0.77)and 0.61(95% CI=0.50,0.74)respectively.The results in the subgroups were all in line with the overall,except for the overweight participants from the urban region.Conclusions:Baseline BMI and dynamic BMI both show a reduced risk of death among overweight men;dynamic BMI shows a lower all-cause mortality in overweight women,and reduced risk of death among obese men and women,but baseline BMI not.Part three Overweight-Years /Obesity-Years,the Combination of Degree nd Duration of Overweight / Obesity,and the risk of all- ause mortality among Chinese adultsObjectives:Overweight-Years and Obesity-Years are better indicator of the health risks(such as diabetes,cardiovascular disease and cancer)than BMI or duration of obesity alone.While the number of years lived with obesity is directly associated with the risk of mortality.This study aims to analyze the association between the duration together with degree of overweight /obesity and the risk of all-cause mortality,and to explore whether the OverweightYears and Obesity-Years are better indicator for the risk of death.Methods:Participants from the survey of the China Health and Nutrition Survey from 1989 to 2009 with BMI information and survival status,free of being underweight all through the follow-up,were included(n=16,680).The variables,overweight-years /obesity-years,were defined by multiplying for each participant the number of BMI units above 24 kg/m2 or 28 kg/m2 by the number of years lived at that BMI.As categorical variables,overweight-years was grouped into intervals of 1–24.9,25–49.9,50–74.9,75-99.9,100-124.5 and ?125;while,obesity-years was grouped into intervals of 1–24.9,25–49.9,50–74.9 and ?75.Cox proportional hazard models were applied to determine the all-cause mortality risk associated with Overweight-Year and Obesity-Year adjusted for potential confounders,and compared with other models using the Akaike information criterion(AIC).The lowest AIC indicated better fit.Furthermore,trajectories of the associations were estimated using a cubic growth model.Results:According to the exclusion criteria,there are 16,680 participants were included in this study(7,848 were men;8,832 were women).During a mean follow-up period of 15.2 years,there are 1,311 deaths.In the overweight-years categories,the all-cause mortality rate is the lowest of 75-99.9 overall(1.1 per 1,000 person-years).Adjusted for age,gender,region,smoking status and drinking status,the hazard ratios of mortality for the categories 1–24.9,25–49.9,50–74.9,75-99.9,100-124.5 and ?125 overweight-years were,respectively,0.69(95% confidence interval(CI): 0.57,0.82),0.53(95% CI: 0.39,0.71),0.29(95% CI: 0.16,0.52),0.25(95% CI: 0.10,0.60),0.54(95% CI: 0.24,1.20),and 0.50(95% CI: 0.19,1.33)compared with zero overweight-years.Significantly protective effects were found in the categories of 1–24.9,25–49.9,50–74.9 and 75-99.9 overall.Similar results were also observed in men,rural and never smoking participants.While among the ever smoking participants,never and ever smoking participants,protective effects were observed in the categories of 1–24.9,25–49.9 and 50–74.9.Notably,in women the lower risk of death was found in the categories of 25–49.9,50–74.9 and 75-99.9;meanwhile there is no effect on the mortality ether from obesity-years or overweight-years in the urban participants.The all-cause mortality rate is the lowest in the obesity-years category of 1-24.9 overall(2.4 per 1,000 person-years).The hazard ratios of mortality for the categories 1–24.9,25–49.9,50–74.9,and ?75 obese-years were,respectively,0.61(95% confidence interval(CI): 0.42,0.89),0.63(95% CI: 0.34,1.18),0.33(95% CI: 0.08,1.32),and 0.28(95% CI: 0.04,1.98)compared with zero obese-years.Significantly protective effect was only found in the category of 1–24.9 overall.Similar results were also observed in women,rural participants,never smoking participants as well as ever drinking participants.Correspondingly,the hazard ratio of mortality for the category of 1–24.9 was 0.56(95% CI: 0.31,0.99),0.39(95% CI: 0.22,0.69),0.60(95% CI: 0.37,0.97),0.55(95% CI: 0.31,0.95).The AIC was lowest in the model containing overweight-years /obesity-years compared with models containing either the degree or duration of obesity /overweight alone.Conclusions:The all-cause mortality is the lowest when the Overweight-Years is 70 or Obesity-Years is 25. |
PDF Full Text Request