Changes In Distribution Of Waist Circumference And Trends Of Central Obesity And Its Influence Factors

BackgroundInternational surveillance data and a number of studies have shown that central obesity and waist circumference appear to be increasing globally. Central obesity is one of the risk factors of several Chronic Non-Communicable Diseases. However, previous studies mostly focused on the mean value changes of waist circumference over time, and rarely on the change of distribution and its socio-demographic factors.ObjectiveTo understand the tendency of waist circumference distribution and trends of central obesity among Chinese adults aged18-65years in nine provinces from1993to2011, and to examine effects of variables of individual, family and community on different quantile of waist circumference.MethodsThis study used data from the China Health and Nutrition Survey (CHNS), an ongoing longitudinal cohort study. According to the aims of the present study, study subjects were divided into two groups. The first group includes those adults aged18-65years who participated in at least one wave of surveys between1993and2011(excluded individuals from BeiJing, ShangHai, ChongQing). LMS curves were used to describe the trends of waist circumference distribution and trends of central obesity. The second group was those participants who joined in the survey at least two times. The longitudinal quantile regression was applied to establish the waist-time model, analyzing its characteristics and influencing factors. 1. From1993to2011, the overall level of waist circumference of18-65years old adults in China’s nine provinces increased, and the percentage of those who have a large waist circumference rose. The change in the range from1993to2004is bigger and smaller margins between2004and2011. Men grow more than women. So no matter which standard was used to defined central obesity, central obesity among this population showed a trend of increase.2. All the percentile curves show increasing trends from1993to2011, and the levels increased more at higher percentile levels, for both genders and in every age group. Waist circumference of male was generally higher than female in all ages. Waist circumference of men over the age of30rose faster than those under30, and women over the age of40rose faster than those under40. The size of the female’s waist change with age is greater than the male’s. Between the ages of18and30, men’s waist level increases fastest, and then tends to decline after50. Women’s waist level increased the fastest between the ages of25to50.3. Between1993and2011there was an upward trend of central obesity. The rate of pre-central obesity and central obesity of men rose more rapidly than that of women. People aged46-65had higher rates of pre-central obesity and central obesity than those aged18-45. The rate of central obesity among men increased gradually along with their education levels, family income and urbanization level increased. While the rate of central obesity among women had little difference between different income levels, but it decreased gradually with their education levels and urbanization level increased.4. During the period1993-2011, about1/3to2/3of men who was identified as overweight by BMI were central obesity, while the proportion of whose identified as obesity was more than80%. This situation was more significant in women than that in men. In addition, central obesity also took place in people who were identified as normal weight or even low weight. Taking both the pre-central obesity and central obesity into account, no matter male or female, more than4/5of overweight people had abnormal waist circumference. 5. No matter men or women, regardless of the level of urbanization, central obesity rates rose during past18years in overweight people defined by BMI, and the rates of pre-central obesity and central obesity were also increased in people of normal weight, moreover the rate of central obesity rise more obviously. The rates of pre-central obesity and central obesity were higher in the high urbanization regions than low and medium urbanization regions.6. The tendency of the distribution of waist circumference with time was strongly influenced by individual factors, while the family and community factors had smaller impact. Age, education, BMI, community urbanization were risk factors, and physical activity was protective factor for men. To high percentiles of waist distribution of men, age, BMI, education were risk factors, whose effects were larger, and community urbanization was less effective risk factors, physical activity was protective factor. Age, BMI were risk factors for women. To high percentiles of waist distribution of women, education, physical activity, sit-in leisure time and family annual income were protective factors.ConclusionsThe tendency of waist circumference distribution with time was strongly influenced by individual factors, while the family and community factors had smaller impact. Age, education level, BMI and community urbanization were risk factors, and physical activity was protective factor for men. For high percentiles of waist distribution of men, age, BMI and education level were risk factors, whose effects were larger, and community urbanization was less effective risk factors, physical activity was protective factor. Age and BMI were risk factors for women. For high percentiles of waist distribution of women, education, physical activity, sedentary time and family annual income were protective factors.