Nepal Journ

Background:In India, non-asthmatic hospital admission case study has been conducted to find out the relationship between obesity and lung functions. The main objective of the present study was to find out the alterations in lung functions due to obesity among Indian population living at National Capital Region (NCR). Materials and Methods:We examined 609 non obese and 211 obese subjects in a cross sectional study from National Capital Region, India with age group ranges between 18-70 years. BMI and body fat % was determined using body fat analyzer. Obese and non-obese subjects were classified based on criteria for BMI and Body fat %. Lung function test viz., FEV1 and PEFR were conducted using portable spirometer (PIKO-1). Results:A significant correlation (p<0.05) was observed between BMI and PEFR among non-obese male and female subjects. Decline in PEFR and FEV1 values for corresponding increase in body fat % was observed among study subjects. A significant (p<0.01) decline in mean FEV1 and PEFR was observed among non-obese and obese subjects, compared to their Indian reference standards for lung functions. A significant negative correlation (p<0.01) was observed between body fat % and lung functions (FEV1, PEFR). Conclusion: It is concluded that obese subjects are at a risk of lung function impairment, based on the criteria followed for BMI and body fat %. The study also demonstrate that body fat% classification as a better index for determination of obese subjects compared to BMI classification, with respect to lung function impairments. Keyword: Body fat%; BMI; lung function; obesity eISSN 2091-0800


Introduction
Obesity has been defined as a chronic medical condition which is characterized by an excessive fat accumulation of human body, causing a general increase in body mass [1]. Obesity is calculated from Body Mass Index (BMI), which is derived from weight in kg divided by height in square meter [1]. World Health Organization reports that obesity has reached epidemic proportions, with 1.9 billion adults being overweight, among which 600 million people are obese [2]. Reports indicate that the global prevalence of obesity has doubled from 1980 to 2014. Approximately 13% of the world's adult population (11% men and 15% women) were obese in 2014 [2]. According to the Global Burden of Disease (GBD) study, 2013 the number of overweight and obese people in South Asia are around 200 million with 150 million overweight and obese subjects in India 3 . The 2013 report also shows prevalence of 19.5% overweight and obese in India [3]. The association between obesity and asthma is observed among women [4,5,[6][7][8][9][10][11][12][13] and men [14][15][16][17]. Obese individuals are more susceptible to obstructive sleep apnea, cardiovascular, pulmonary, hepatic, renal diseases, metabolic alterations and neoplasm [18].Some research groups mentioned earlier has studied the role of adiposity on the respiratory functions, however no consensus ever reached on the physical mechanisms leading to respiratory complications [19].Obesity affects the respiratory functions in many ways. The adipose tissue deposited around the rib cage, abdomen and visceral cavity affects work of breathing and reduces the pulmonary functions [20]. Impedance to diaphragmatic contraction and flattening is imposed by the abdominal adipose tissue, which generates an inspiratory load and imposes pressure on the lungs to optimally inflate and deflate the lungs during tidal respiration [21]. The ribcage movements are also restricted by the thoracic and sub-pleural fat which imposes additional restrictive forces on the lungs. Adiposity can lead to reduced lung compliance [22][23][24].Obesity can lead to increase in pulmonary blood volume, closure of airways, atelectasis and increased alveolar surface tension [25]. Obesity can result in respiratory function impairment [26], but there are few reports which showed no relationship between them [27,28]. This difference of opinion is mainly due to BMI classification, which will not reflect the distribution or quantity of fat and lean tissue [29]. High BMI in adults was associated with reduced FEV1 and FVC30-32. FEV1/FVC ratios are dependent on alterations in FEV1 and FVC [33,34]. In India, according to the National Family Health Survey (NHFS), the percentage of women in the age group 15 -49 years who are overweight or obese increased from 10.6% in NFHS-2(1998-99) to 14.8% in NHFS-3(2005NHFS-3( -2006. The NHFS-3 data also reports 12.1% men in the age group 15 -49 years being overweight or obese [35]. According to a recent estimates, over 74% of the urban Indians are overweight [36]. Another study showed that one in every five men and one in every seven women in India are extremely obese in India with average BMI being 27.5 kg/m2 and 30 kg/m2 respectively. In India, chronic respiratory disease accounts for 7 per cent of all deaths and 3 per cent of DALY'S [37]. In an earlier study, tobacco smoking habit was associated with chronic respiratory morbidity [38]. Environmental tobacco smoke [39] and biomass fuels [40,41] are associated with chronic respiratory morbidity among women and children [42]. Differences in pulmonary function in normal people may be due to ethnic origin, physical activity, environmental conditions, living at high altitude, tobacco smoking, age, height, sex, and socioeconomic status.' The wide range of geographical and climatic conditions in India where regional differences in lung function among healthy individuals can be observed [43].Obesity related asthma was observed among adult and paediatric population [4,5]. Even though there are studies which show relationship between asthma and adiposity, there are few studies with difference of opinion [30,[44][45][46][47][48][49]. Considering the proportion of overweight and obese people in India as well as respiratory health problems among Indians, a cross sectional study was conducted to understand the association between obesity and lung function status among residents of National Capital Region, India.

Study design and participants
A cross-sectional study was done between 1 st March-31 st September 2010. The eligible subjects were selected from the semi-rural areas of Gurgaon and Noida region in the National Capital Region (NCR), New Delhi, India. Households were selected using systematic sampling scheme using the list of all households in the region from government agencies. The identified residents were asked to participate based on their voluntary informed consent. Participants were free to withdraw at any stage of the study.

Data collection
The personal details comprising of information regarding age, height, weight, body composition measurements (BMI and Body Fat%) and personal habits were recorded through structured personal interviews. BMI and Body Fat% (BF%) was measured using a body fat analyzer (HBF-352, Omron Health care Co., Kyoto, Japan). BF % and Body weight was measured to the nearest 0.1 per cent and 0.1 kg respectively in light indoor clothing without shoes, using body fat analyzer. Height was measured using portable Stadiometer. BMI > 25 kg/m 2 were considered as obese subjects and BMI < 25 kg/m 2 were taken as non-obese, based on the Indian guidelines issued by the Ministry of Health, Govt. of India [50]. In case of BF%, the criteria of obesity were taken separately for male and female subjects. In case of male subjects BF% > 25 were considered obese and < 25 as non-obese. For female subjects, obesity was defined as BF% > 39 [51]. Lung function tests FEV 1 (Forced Expiratory Volume in 1 second) and PEFR (Peak Expiratory Flow Rate) for assessment of pulmonary impairment were carried out using a portable Spirometer (PIKO-1, UK) following the recommendation of the American Thoracic Society standards). Each subject performed the lung function test three times after allowing necessary rest between repetitions. The best value of PEFR and FEV 1 among the three tests for each subject were recorded. Results of lung function parameters were compared with their predicted values for Indian population [52].

Inclusion criteria
The inclusion criteria for the selection of subjects were age group between 18 and 70 years who live in the study locations. A total of 820 subjects were found eligible for the study.

Exclusion criteria
Subjects taking any form of medication were excluded from the study. Further all the subjects who doesn't follow the inclusion criteria were excluded from the study.

Outcome variable
The main outcome variable of the study was the status of the lung function parameters (FEV 1 and PEFR).

Explanatory variable
Body composition variables (BMI and BF%) were taken as the explanatory variables.

Ethical Statement
Ethical clearance was obtained from CSIR-Indian Institute of Toxicology Research-Institutional Human Ethical Committee (IHEC), Lucknow, India before starting the study.

Sample size calculation
In a pilot study done prior to the study with 100 cases showed Proportion of respiratory symptoms in group I = .25,Proportion of Respiratory symptoms in group II = .16. With risk difference = 0.09, Power(%) = 80, alpha Error(%) = 5, required sample size for each arm was 315. Data management and statistical analysis Subjects were divided into obese and non-obese as per their BMI and BF% classification. Descriptive statistics (mean, standard deviation and range) was calculated for all the continuous variables. All the categorical variables were presented as frequencies with their percentage. Student's t test was used to check for significance between the mean values of the quantitative parameters (age, height, weight, FEV 1 and PEFR). Age adjusted comparisons were undertaken using generalized linear models. Smoking status of the study subjects has been adjusted in the analysis. Chi square was used to test the significance in case of categorical variables Regression models were fitted taking FEV 1 and PEFR as the dependent variables and BMI & BF% as the independent variables. Models were then used to predict the values of FEV 1 and PEFR with increasing or decreasing values of body composition factors. The criterion of significance was taken as p<0.05. All statistical calculations were done using STATA IC 13 software.

Results
A total of 820 eligible subjects were selected for the study based on the inclusion and exclusion criteria. Table 1 summarizes the characteristics of the study subjects stratified according to BMI and BF% classification for obese and nonobese. When stratified according to BMI, a total of 609 subjects were non-obese and 211were obese according the criteria adopted. Prevalence of obesity was higher among females (p<0.01). Significantly higher number of obese males was found in the stratification by BF%. Obese subjects based on BMI and body fat % were older (as per their average age) than non-obese subjects (p<0.01). Hence, age was adjusted for statistical analysis. Height was more or less similar in both groups. Body weight among obese subjects was higher with BMI and body fat % classification. Smoking was significantly more (p<0.01) among non-obese subjects in BMI classification. Hence, smoking effect was adjusted for statistical analysis. Respiratory symptoms were more (p<0.05) among obese subjects. Table 2 shows decline in PEFR and FEV 1 predicted % for increase in body fat %. The percentage fall in the PEFR was 1.6 -4.8% corresponding to increase in body fat %. In case of percent predicted FEV 1, the decline was observed from 1.5 -4.2% corresponding to increase in body fat%. No such alteration in lung function was observed for increase in BMI. Figure 1 showed significant decline in observed FEV 1 and PEFR among non-obese and obese subjects (p<0.01) with respect to both body fat % and BMI classification. Pooled analysis shows negative correlation (p<0.01) between increase in body fat % and pooled values of FEV 1 and PEFR among study subjects (Figure2). This relationship was not observed for BMI classification.

Discussion
This study is the first report on the risk of decline in FEV 1 , PEFR among obese subjects in Indian population, based on the criteria followed for BMI and body fat %. In an earlier Indian study a similar report on decline in FEV 1 based on BMI classification were reported in non-asthmatic hospital based study [58]. The significance of the present study is the selection of subjects who are residents at National Capital Region and not having any previous history of serious medical illnesses.
The study also demonstrate that body fat% classification as a better index for determination of obese subjects compared to BMI classification, with respect to lung function impairments. The effects of obesity on the lung function values have not been found to be consistent in earlier studies [58]. Other studies (other than from India) have reported effects of obesity on asthma [53], reduced FRC and expiratory reserve volume detected even at modest increase in weight [25], significant inverse relation between BMI and values of VC and TLC and the values of FRC and ERV decreasing exponentially with BMI [54], reduced FRC in obese subjects [55] and extreme obesity associated with a reduction in ERV, FVC, FEV 1 , FRC, FEF 25-75 %, and MVV [56]. Several studies reported no significant differences in FEV 1 , FVC, FEV 1 /FVC ratio and FEF  between obese and non-obese subjects [1,57,58]. Obesity is the combination of fatty mass and body masculinity, whereas BMI can interpret only body structure [57,59,60].The effects of body fat% on the pulmonary function values have also been examined in the present study, a topic which hasn't received much attention. Our study showed body fat% to be a better indicator of the lung function alterations as compared to BMI. Generally FEV 1 and FVC are within the normal range among healthy obese subjects [1,25]. Restrictive type of lung function abnormalities are frequently observed among obese subjects responsible for alteration in respiratory mechanics [60]. Abdominal and thoracic fat deposition are associated with work of breathing [60,61]. Our results indicate a significant decline in the predicted values of both FEV 1 and PEFR with increasing body fat%. Studies conducted on the lung function status of patients have indicated upper body obesity has a more severe impact on the lung volumes as compared to obese patients with lower body obesity [57]. Increase in body fat is associated with decline in FEV 1 and FVC by 10 -15 mL [28,60]. Therefore it can be presumed that adiposity impacts negatively on the lung functions [57,59,60]. Abdominal obesity is related to FEV 1 and FVC, whereas body fat alone does not show any relationship with lung functions [60]. Exercise regimens may be adopted as an intervention strategy among obese subjects to improve health. Exercise may generate deep inspiration and tidal volume which reverses broncho-constriction [62,63]. Reductions in lung function values can be associated to the ambient air pollution in the study locations. Lack of individual exposure data is a limitation of the study.

Conclusions:
It is concluded that obese subjects are at a risk of lung function impairment, based on the criteria followed for BMI and body fat %. The study also demonstrate that body fat% classification as a better index for determination of obese subjects compared to BMI classification, with respect to lung function impairments.

Limitation of the study:
The study subjects were restricted to National Capital region which can be considered as a limitation. The data was not adjusted to exposure of air pollutants in the study locations, which can be considered as another limitation of the study. Future scope of the study: Future studies must be extended to a larger, geographically and anthropometrically diverse national representative population in India, to enable a better policy decision on this aspect. Further studies are required on the association of obesity on lung functions to find out its relationship in a larger, national representative sample size in India. What is already known on this topic: Previous studies showed an association between body composition factors like BMI, body fat % and its effects on lung functions. These studies are focused among patients at hospital settings. What this study adds: This is the first population-based study on the relationship between body composition factors and alterations in lung functions among Indian population especially residents at National Capital Region with a large sample size. Author's affiliation: