Association of body mass index with pulmonary function in overweight young adults.
Obesity is the most common metabolic disease in the world  with its prevalence increasing over several decades.  Formerly thought to be a problem of developed countries, it has now become an important worldwide contributor to morbidity and mortality among all ages and socioeconomic groups.  Besides genetic predisposition, adoption of sedentary lifestyle and inappropriate intake of calorie-rich easily available junk food has made the environment conducive to the development of obesity even in childhood.  Patterns of diet and exercise developed in childhood are difficult to change as one grows up thus making childhood obesity a strong risk factor for adult obesity which is linked with a higher chance of premature death and disability. 
Obesity has been associated with the increased incidence of cardiovascular diseases, hypertension, metabolic disorders, and pulmonary dysfunction.  Obesity can have detrimental effects on respiratory functions, such as alterations in the respiratory mechanics, decrease in respiratory muscle strength and endurance, decrease in pulmonary gas exchange, lower control of breathing, and limitations in pulmonary function tests (PFT).  These changes in lung function are caused by fat accumulation in the chest wall and abdominal cavity, compressing the thoracic cage, diaphragm, and lungs, consequently causing a decrease in diaphragm displacement, adecrease in lung and chest wall compliance, and an increase in elastic recoil, resulting in a decrease in lung volumes, and an overload on inspiratory muscles, impairing ventilatory function. [7-9] Furthermore, the deposition of extra adipose tissue on the chest wall has negative effects on the expansion and excursion of the rib cage, through a direct loading effect or by altering intercostal muscle function.  It has been pointed out by various studies that increased body mass index (BMI) is related to a reduction in lung function parameters and is also related with markers of systemic and vascular inflammation (C-reactive protein and leptin) thus suggesting that the maintenance of adequate body weight might prove essential for improving the lung function. [11-14]
Even though the interaction between obesity and PFT has been addressed previously, the results have been inconsistent among the overweight young population. Therefore, we aimed to evaluate the effects of BMI on pulmonary function in overweight young adults.
MATERIALS AND METHODS
A total of 100 overweight medical students (50 males and 50 females) in the age group of 18-25 years, were enrolled for this study. This cross-sectional study was conducted in the Department of Physiology, SKIMS Medical College, Srinagar, from January 2018 to September 2018. The students were informed about the objectives of the study and consent was obtained from them. Institutional Ethics Committee approved the study protocol. Students having a history of asthma, severe anemia, chest or abdominal pain of any cause, or history of any disease which can be expected to affect pulmonary function such as neuromuscular disorder and cardiopulmonary disorder were excluded from the study. All the subjects were nonsmokers. A detailed history was taken from each and physical examination was performed. The finding was recorded in the pro forma. The participants were examined for various anthropometric parameters such as height and weight. Weight was measured using digital scale to the nearest 0.1 kg with only light clothing, and for the determination of height, subjects were made to take off their shoes, stand upright with their head in the Frankfort plane with the heel, buttock, and occiput against the wall. Height was recorded to the nearest 0.5 cm. BMI was calculated as weight (in kg) divided by the square of height (in meters) and those having a BMI of >25 kg/[m.sup.2] were included in the study. PFTs were measured in all the study participants using the Computerized Spirometer, "Shiller's Spirometer." The subjects were asked to avoid tea, coffee, and other stimulants. After a rest for 5 min, the test was carried out. The subject was made to sit in the upright posture and made comfortable. The test was demonstrated and explained in detail to the subjects. At least three tests of acceptable effort were performed to ensure reproducibility and the best trial was selected for reporting. The following parameters were noted forced vital capacity (FVC), forced expiratory volume in one second (FEV1), FEV1/FVC, and peak expiratory flow rate (PEFR). All spirometric parameters were considered as a percentage of predicted on reported height and age.
Data were collected and grouped using MS Excel. Mean and standard deviation were calculated. Statistical software SPSS version 20 was used for the analysis of the data. Student's unpaired t-test was adopted to compare the pulmonary function measurements and physical parameters between the genders. Pearson's correlation test was used to find the correlation of BMI with respiratory parameters in both genders.
Among the 100 participants, 50 (50%) were males and 50 (50%) were females. All the mean values were slightly higher in males except for BMI which was slightly higher in females. The significant gender difference was found in FVC, FEV1, and PEFR (P < 0.001) [Table 1].
The correlation was assessed between BMI and the lung function parameters. Table 2 depicts the Pearson's correlation coefficient (r) between BMI and PFT parameters in male and female subjects. Among all pulmonary function parameters, BMI correlated significantly with PEFR in both males and females.
In the present study, we tried to find out the effect of BMI on lung function parameters. Mean values of lung function parameters, namely FVC, FEV1, and PEFR were found to be significantly higher in males when compared to females. Previously conducted studies have also reported significant gender differences in lung function parameters. [15,16] Females have lower values for lung function parameters as their respiratory muscle endurance, and chest wall compliance is lower than males.  In addition to the anatomical and physiological differences, certain other factors such as sex hormones, sex hormone receptors, or intracellular signaling pathways may also be responsible for the gender difference in lung functions. [18,19]
It was observed that there was no significant relationship between BMI and FEV1, FVC, and FEV1/FVC in both genders, however, a significant relationship was observed between BMI and PEFR in both genders. In most of the previously conducted studies, the effects of BMI on lung function parameters are not consistent, with some studies showing significant effects [20-23] while others showing no effects. [24-27] Results similar to ours were reported by a study conducted in South India in apparently healthy adults (both obese and nonobese).  These differences in findings of various studies could be due to methodological differences, differences in the age group of the study population and also due to the fact that we included only overweight adults in this study. A study conducted among Indian adult males showed that obesity itself and more specifically the pattern of body fat distribution have independent effects on PEFR.  In healthy subjects, primary factors that affect PEFR are the strength of the expiratory muscles generating the force of contraction, the elastic recoil pressure of the lungs and the airway size.  In obesity, the function of respiratory muscles is impaired from the increased resistance they must overcome and from the reduced capacity of these muscles.  Hence, in addition to indicating that increased BMI has effects on the lung function that can cause a decrease in respiratory well-being, our study is an attempt to make overweight individuals aware about the ill effects of obesity and encourage them to adopt a healthy lifestyle to prevent the development of respiratory complaints later in life.
The strength of our study is the recruitment of subjects who were overweight but without any comorbid condition. The limitations include small sample size and all the lung function test parameters, and lung volumes were not recorded. Furthermore, the relation of pulmonary function with other markers of obesity was not explored. There is a need for conduction of longitudinal studies with larger sample size, keeping in view the distribution of body fat.
This study showed that there exists a significant correlation between BMI and PEFR (an objective measure of airflow resistance in the lungs) in both genders suggesting an increased pulmonary risk with increased BMI.
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Nida Nowreen, Farhana Ahad
Department of Physiology, SKIMS Medical College, Srinagar, Jammu and Kashmir, India
Correspondence to: Nida Nowreen, E-mail: email@example.com
Received: October 07, 2018; Accepted: November 02, 2018
Source of Support: Nil, Conflict of Interest: None declared.
Table 1: Baseline characteristics and pulmonary function parameters of the subjects Variable Males Females p value (mean[+ or -]SD) (mean[+ or -]SD) Age (years) 19.95[+ or -]1.33 19.24[+ or -]1.50 NS Weight (kg) 67.69[+ or -]7.66 66.15[+ or -]7.34 NS Height (cm) 1.68[+ or -]0.07 1.59[+ or -]0.08 NS BMI (kg/[m.sup.2]) 26.73[+ or -]2.65 27.01[+ or -]2.59 NS FVC (L) 3.89[+ or -]0.32 2.36[+ or -]0.20 <0.001 FEV1 (L) 3.24[+ or -]0.57 2.03[+ or -]0.49 <0.001 FEV1/FVC (%) 86.23[+ or -]6.58 87.67[+ or -]7.67 NS PEFR (L/min) 408.04[+ or -]57.56 319.27[+ or -]66.88 <0.001 BMI: Body mass index, FVC: Forced vital capacity, FEV1: Forced expiratory volume in first second, PEFR: Peak expiratory flow rate. (*) P<0.05, (**) P<0.001, NS: Not significant Table 2: Correlation of spirometric parameters with BMI in male and female subjects Gender Parameter r p value Males FVC (L) 0.122 0.399 FEV1 (L) 0.205 0.154 FEV1/FVC (%) 0.273 0.081 PEFR (L/min) -0.302 (*) 0.033 Females FVC (L) -0.117 0.417 FEV1(L) 0.221 0.123 FEV1/FVC (%) 0.225 0.116 PEFR (L/min) -0.332 (*) 0.018 FVC: Forced vital capacity, FEV1: Forced expiratory volume in first second, PEFR: Peak expiratory flow rate. (*) P<0.05, (**) P<0.001
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|Title Annotation:||RESEARCH ARTICLE|
|Author:||Nowreen, Nida; Ahad, Farhana|
|Publication:||National Journal of Physiology, Pharmacy and Pharmacology|
|Date:||Jan 1, 2019|
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