ABSTRACT
Objective:
The aim of this study was to evaluate whether exposure to second-hand smoke affected the six-minute walk test (6MWT) of obese non-asthmatic pediatric cases.
Methods:
Obese pediatric patients (body mass index >95th p) with no existing co-morbidities were included in the study. Smoke exposure was assessed with a self-reported questionnaire completed by the parents. The subjects were divided into two groups: Group 1 consisting of obese children exposed to passive smoking and Group 2 of obese children not exposed to passive smoking. In addition to 6MWT, spirometric flow and volume, including forced expiratory volume in 1 s and peak expiratory flow rate, were also measured in all subjects. The results of the 6MWT were assessed to determine any association with passive smoking.
Results:
The study included 75 obese pediatric cases (40 male, 35 female) with a mean age of 9.06±0.97 years. The 6MWT results in Group 1 was 501.88±62.12 meters and in Group 2 559.63±72.93 meters. The difference was statistically significant (p=0.001).
Conclusions:
Passive smoking may negatively affect the respiratory and cardiovascular capacity in obese children, who are already at risk of lower cardiopulmonary function. The evaluation of 6MWT in these pediatric patients may be useful for monitoring and families should be warned about potential problems due to smoking.
Introduction
The leading preventable health risks today are smoking and obesity. The incidence of several cardiovascular risk factors including high blood pressure, dyslipidemia and metabolic syndrome, is linked to childhood exposure to tobacco. Obesity also exerts its negative effects on arterial structure via increased intima-media thickness and function through decreased elasticity and endothelial function (1). In the past thirty years, the rate of obesity has increased fourfold in children aged 6-11 years (2). Endothelial dysfunction and increased cardiovascular morbidity and mortality are linked to habits and states leading to insulin resistance, such as smoking and obesity (3). Overweight or obese children are at higher risk of being affected by existence of smoking in the family (4). Being a passive smoker is known to be nearly as harmful as being an active smoker. Exposure to environmental tobacco smoke affects children most, as children breathe more frequently than do adults and thus inhale more environmental tobacco smoke (5). The implementation of laws against smoking in the workplace and public areas has left the home as the dominant unregulated source of exposure to smoking. This has significant effects on children who cannot remove themselves from the environment filled with tobacco smoke (6).
Decreased fitness and decreased aerobic capacity have been linked to increased weight in adults (7). Impaired cardiopulmonary status in obese pediatric patients can also limit the functional capacity and have negative effects on ability to partake in exercise. The six-minutes walk test (6MWT) is a simple, practical, standardized, reliable and valid measure of effect of submaximal exercise in healthy children (8,9,10). The test reflects the state of cardiopulmonary fitness in addition to state of physical activity in daily life and is considered to be the most relevant walk test (8). Disability in obese subjects has been reported in previous studies using the 6MWT (11).
The aim of this study was to determine whether exposure to passive smoking affected the 6MWT results in non-asthmatic obese pediatric cases.
Methods
This case-control study was conducted in the time period between December 2013 and May 2014 at Çanakkale Onsekiz Mart University Hospital. In this study, we enrolled a total of 75 children (M/F=40/35) with a mean age of 9.06±0.97 (min:7-max:10) years with a diagnosis of exogenous obesity and no co-morbidities including hypertension, impaired cardiac function, glucose intolerance, hyperlipidemia, hypothyroidism. Exclusion criteria were also neuromuscular disorders and ataxia, mental retardation, cerebral palsy, systemic disease affecting the respiratory tract directly or indirectly, chronic or acute disease affecting the respiratory tract directly or indirectly, use of inhaled corticosteroids, bronchodilators or other medication affecting the respiratory tract, history of recent or chronic respiratory disease, history of severe respiratory disease, i.e., congenital lung disease, hospitalization for pneumonia or thoracic surgery. Three children with hypertension and 2 children with glucose intolerance were subsequently excluded. To ensure compliance, only children over the age of 7 were included in the study. The etiology of obesity in the patients had been previously investigated and follow-up was being conducted by the pediatric obesity clinic. Our hospital is a tertiary center, which explains its higher prevalence of obesity as compared to the general population. This is one reason why we chose to perform the present study in our hospital.
Exogenous obesity was defined as obesity not linked with any endocrine, metabolic or genetic causes. The parents of all children were asked to answer a questionnaire comprising the child’s demographic characteristics and his/her history of exposure to passive smoking.
The participants were then divided into two groups. Group 1 consisted of obese children exposed to smoking and Group 2 of obese children who were not exposed to smoking. None of the participants were reported to have followed a regular exercise program. The study was approved by the Çanakkale Onsekiz Mart University Research Ethics Committee and all parents provided a written informed consent.
Results
Most of the children in the series were born at term with a birth weight between 2500 and 3500 g (min:2000-max:4900) (Table 1). Three patients were born small for gestational age and 4 patients were born large for gestational age.
Mean six-minute walking distance in meters (m) (6MWD) was 501.88±62.12 meters in Group 1 and 559.63±72.93 meters in Group 2. The difference was statistically significant (p=0.001).
With the exception of 2 patients in Group 1 and 2 patients in Group 2, all subjects were breastfed. Duration of breastfeeding in the two groups is given in Table 1. When all patients in the study were evaluated, 6MWD had a positive correlation with the duration of breastfeeding (r=0.345, p=0.02).Female patients in Group 1 had shorter 6MWD results than the girls who were not exposed to passive smoking and the difference was statistically significant (Table 2).
In Group 1, 26 mothers smoked (mean duration 11.4 years) and 31 fathers smoked (mean duration 15.9 years). For smokers, including both mothers and fathers, minimum and maximum smoking duration was 5 and 20 years, respectively. Passive smoking status of the parents and its association with 6MWD are given in Table 3.
6MWD values of children with both parents who smoked were found to be significantly shorter than those with only mothers who smoked (p=0.046) (Mann-Whitney U test).
Discussion
Our study demonstrated that obese pediatric patients who were exposed to passive smoking had shorter 6MWD than obese children who were not. Passive smoking is a well-known risk factor for reduced respiratory capacity (19). Our study population was investigated with this in mind and patients with normal respiratory capacity were included in the study. Passive smoking causes antioxidant depletion increasing systemic inflammation and sensitivity to other oxidant stresses (20), which is already increased in obesity (21). Coexistence of obesity and passive smoking may increase oxidant stress. On the other hand, in a recent study by Pavic et al (22), the children of smoking parents were found to have higher BMI than children of non-smoking parents. In the same study, 6MWT was also performed on children of smoking and nonsmoking parents and impairment of physical condition, especially in children with both parents smoking, was shown. Our study population consisted of children who were already obese and the BMI values were higher in children exposed to tobacco smoke than in those who were not, but the difference was not statistically significant. Our study also showed that 6MWD was shortest for children whose parents both smoked. In the passive smoking group, 6MWD of only mothers who smoked was significantly longer than those where both parents smoked.
Adverse respiratory effects are more strongly linked to paternal smoking in infants when the mother does not smoke, according to Cook and Strachan (23). Blackburn et al (24) reported that the major contributor to total tobacco consumption in a household is the father. These results may be due to infants spending more time with the mother than the father. 6MWD was found to be mainly dependant on age (25). In our study also, the younger children (those aged 7 years) were more affected compared to other ages and this group was also the group most affected by exposure to smoke. This may be due to the increased time spent by younger children in the company of parents. After the age of seven, the time spent in school limits the time in the home, leading to less exposure to smoke. However, there was no correlation between duration of exposure and 6MWD in our correlation analysis. We believe further studies with larger populations and older age children will further clarify the difference due to duration of exposure.
Current guidelines state that the 6MWD is influenced by sex (18). 6MWD values showed no differences between girls and boys in the present study. However, our study results demonstrated that girls who were exposed to tobacco smoke had shorter 6MWD than girls who were not.6MWD had a positive correlation with duration of breastfeeding in this study, indicating that it is both prophylactic and preventive. Lower rates of obesity are linked to breastfeeding, which has a protective affect against obesity in later life (26). Yilmaz et al (27) found that breastfeeding promoted the growth of infants who were passively exposed to tobacco smoke and it is advised that breastfeeding should be promoted to protect infants against the health hazards of passive smoking. It primarily protects against obesity and secondarily prevents cardiopulmonary complications in obese patients.To the best of our knowledge, this is the first study evaluating the effect of passive smoking on 6MWT in obese pediatric cases. Passive smoking in obese children, already a risk group, may result in greater decline in cardiovascular and pulmonary function. Evaluating 6MWT in these patients may be useful for monitor and families should be warned about potential problems due to smoking. While smoking is a modifiable risk factor, to reduce the obesity-related disease burden exposure to passive smoking should be avoided to improve the health of these patients by educating parents, especially through public health programs.