Comparable Obesity Parameters with Lung Function in A Chinese Rural Adult Population

Background: To assess association between di ﬀ erent obesity parameters and lung function indicators in a Chinese rural adult population. Methods: A total of 8,284 Chinese adults aged 20 to 80 years old from Xinxiang were recruited in this study. Obesity parameters including BMI, waist circumference (WC), hip circumference (HC), waist hip ratio (WHR), waist height ratio (WHtR), body fat percentage (BFP), basal metabolism (BM), and visceral fat index (VFI) and lung function parameters such as forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV 1 ) were measured according to previous guidance. Results: The total prevalence of obesity dened by BMI, WL, WHR, WHtR, and BFP were 23.2%, 58.2%, 66.7%, 69.2%, and 56.5%. In general, the prevalence of obesity in women was higher than that in men. The average levels of FVC and FEV 1 in participants were 3.19 ± 0.72 (L) and 2.68 ± 0.64 (L), respectively. Men have a higher lung function levels than that of women. Lung function levels in obesity group were lower than those in non-obesity group, regardless of gender. Spearman correlation analyses showed that obesity parameters including BMI, WC, HC, WHR, WHtR, BFP, BM, and VFI were signicantly correlated with lung function levels such as FVC and FEV 1 . After adjustment for the potential confounders in further linear regression analyses, BMI, WHtR, BFP, and obesity dened by BMI, WHtR and BFP were negatively associated with lung function, while WC, WHR, and obesity dened by WC and WHR were positively associated with lung function. Conclusions: Taken together, status closely related to lung function in general Chinese adult population. Weight control and lose important strategy to improve of lung function and reduce of This study investigated the association between obesity parameters and lung function of 8,284 adults from the typical rural areas in central China. Our results show that the prevalence of obesity in this study is in a high level, which is higher than the reported obesity rates in China. Although the prevalence of general obesity dened by BMI was higher in men than that in women, the prevalence of abdominal obesity dened by WL, WHR and BFP were lower in men than those in women. Lung function levels was lower in obesity group when compared with non-obesity group. Spearman correlation analyses showed that these obesity parameters were signicantly correlated with the measured lung function indicators. After adjustment for potential confounders, the dened obesity and obesity-related parameters were negatively associated with lung function parameters such as FVC and FEV 1

included in the analyses of this study. The participants completed a general health questionnaire and underwent routine physical examination. The study protocol was approved by the Human Ethical Committee of Xinxiang Medical University, China. All participants provided their written informed consent before enrollment and data collection.

Questionnaire
Participants were required to complete a questionnaire through face-to-face conversation by trained staff. Physical measurements were conducted using standardized procedures as described below. The questionnaire collected individual basic information including age, gender, marital status, residential address, income, education, and lifestyle characteristics such as smoking habit, and alcohol consumption. The physical examination parameters included body height, weight, WC, HC, BFP and VFI.

Physical measurements
All participants undergo weights, heights, waists, hips, BFP, and VFI measurements according to a standard protocol [19]. Physical examination was measured after participants had taken off shoes and heavy clothes. Weight was measured to the nearest 0.1 kg, height was also measured to one decimal. WC was determined to the nearest 0.5 cm around the abdomen at the level of the umbilicus/belly button, and hip circumference HC was read to the nearest 0.5 cm at the fullest part between abdomen and crotch. Body mass index (BMI) was de ned as weight (kg) divided by the height squared (m 2 ). Waist to hip ratio (WHR) was calculated as WC divided by HC. Waist to height ratio (WHtR) was calculated as WC divided by height. BFP and VFI were measured using Omron HBF-371 body fat and weight measurement scales (Omron, Kyoto, Japan) and bioelectrical impedance analysis (BIA). BFP was de ned by body fat weight divided by total weight. All measurements were taken twice and the average of the two values was used in the further analyses.
De nition of obesity Individuals with BMI ≥ 25 kg/m 2 was de ned as general obesity [22,32]. Central obesity is de ned as WC ≥ 90 cm for men and WC ≥ 80 cm for women or WHR ≥ 0.90 for men and WHR ≥ 0.80 for women or WHtR ≥ 0.5 both for men and women [23]. Obesity is de ned as BFP ≥ 25 for men and BFP ≥ 33 for women [27]. VFI was divided into four categories (from "thin" to "high") according to the criteria in the previous study, respectively [40].

Spirometry
The lung function test was conducted with a portable spirometer (Chestgraph HI-801, CHEST M.I., INC., Tokyo, Japan) in a standing position following the standardized procedures of the ATS-criteria, and at least three measurements and the highest value of forced vital capacity (FVC), forced expiratory volume in the rst second (FEV 1 ), vital capacity (VC), inspiratory capacity (IC), residual volume (RV), tidal volume (TV), expiratory reserve volume (ERV), inspiratory reserve volume (IRV), total lung capacity (TLC), peak inspiratory ow (PIF), peak expiratory ow (PEF), and peak expiratory ow time (PEFT) were used in the analyses [41]. The spirometer was calibrated prior to each test according to the instruction of the manufacturer. Predicted values for FVC and FEV 1 were derived from the equations for Chinese [42]. The lung function and its predicted values, and restrictive respiratory defect were the main outcome variables [43].

Statistical analysis
All data were inputted and established using EpiData version 3.0 software. A statistical analysis was performed using SPSS version 22.0 (IBM Corporation, NJ, USA). The normally distributed continuous variables were presented as the mean ± standard deviation, and are compared using the t test. The nonnormally distributed quantitative data were displayed as median and interquartile range, and compared using the Mann-Whitney U test. Categorical variables were expressed as percentages and were analyzed using the chi-square test or Fisher's exact test as appropriate. Spearman correlation analysis was used to explore the correlation between obesity and lung function parameters. Multivariate linear regression analyses were further carried out to evaluate the association between obesity and lung function. Potential confounders were included in each full model when the p-value of the confounder was lower than 0.05. A value of p < 0.05 was considered statistically signi cant.

Patient and public involvement
No patient involved Result General characteristics of the study population The average age of the men and women participants in Xinxiang county were 52.12 ± 12.42 and 51.23 ± 12.09 years, respectively. The percentage of men and women was 40.2% and 59.8%, respectively. As shown in Table 1, men have a higher current smoking and drinking rate, family income and educational level when compared to women (Table 1). There was no signi cant difference in BMI between men and women (Fig. 2). In addition, height, weight, WL, HL, WHR, BM, and VFI of men were higher than those of women (Table 2). However, WHtR and BFP of men were lower than those of women (Table 2).  The total prevalence of obesity de ned by BMI, WL, WHR, WHtR, and BFP were 23.2%, 58.2%, 66.7%, 69.2%, and 56.5%, respectively. In addition to the percentage of obesity de ned by BMI, other percentages of several kind obesity were higher in women than those in men (Fig. 3). A total of 1891 (22.8%) participants suffered from both general and central obesity. In particular, the distribution of obesity parameters such as BMI and BFP in men is not higher than those in women (Fig. 3). In a word, the prevalence of obesity both in men and women was at a higher level based on this general rural population (Table S1).

Lung function levels
Both FVC and FEV 1 of and their predicted values were higher in men than those in women (Table 2). In addition, FVC and FEV 1 of participants were higher than their predict values. The ratio of FVC to FEV 1 were higher in women than that in men (Table 2). Similarly, other lung function indices such as VC, IC, RV, TV, ERV, IRV, TLC, PIF, PEF were signi cantly higher in men than those of women (Table 2). Moreover, FVC and FEV 1 of participants were signi cantly lower in all different de nitions of obesity than their non-obesity groups, respectively (Fig. 4).

Correlation between obesity parameters and lung function indicators
Spearman correlation analyses demonstrated that several obesity parameters were signi cantly correlated with lung function levels. In particular, BMI, WHtR and BFP were negatively correlated with FVC and FEV 1 . However, WC, HC, WHR, BM, and VFI were positively correlated with FVC and FEV 1 (Fig. 5 and Table   S2). In addition, BMI, WL, WHR, WHtR, BFP, BM, and VFI were negatively correlated with the ratio FVC to FEV 1 (FEV 1 /FVC), while height and hip circumference were positively correlated with FEV 1 /FVC (Table 3). In addition, obesity parameters including BMI, WC, HC, WHR, WHtR, BFP, BM, and VFI were signi cantly correlated most of the other lung function indicators such as VC, IC, RV, TV, ERV, IRV, TLC, PIF, PEF and PEFT (Table S2).
This study had several limitations related to data availability and quality.
Domestic data on obesity in China are de ned differently from international data.
The ndings provide useful suggestions to investigate association between obesity and lung function among Chinese adults.

Conclusion
In summary, both general and central obesity are negatively associated with lung function in general Chinese rural adult population. However, direction of effects for WC and its related WHR on lung function is negative. In particular, height related obesity parameters such as BMI and WHtR have a negative effect on lung function, whereas WC related obesity parameters such as WC and WHR have a positive effect on lung function. Given an inverse association between BFP and lung function, BMI (for general obesity) and WHtR (for central obesity) may be preferred common parameters to assess the relationship between obesity and lung function in general population. However, the underlying mechanism between them needs further investigated.