Investigation of maternal smoke exposure and childhood obesity: A cross-sectional study

Introduction: Recent studies suggest that smoking exposure in pregnancy period might be a risk agent for childhood overweight and obesity. We examined associations between maternal smoking in pregnancy period and children’s weight and the possible obesogenic effects of maternal smoking. Methods: The present study was designed as a cross-sectional analysis of a survey. A 31-question survey was administered to mothers to learn the nutrition and smoking habits in Turkey from January to March 2020. Also, a 25-question survey was administered to children to study their diet. Participants were classified as underweight, normal, overweight, or obese. The smoking status of mothers was also recorded. The data were analyzed using SPSS. Results: The research group consisted of 454 participants (227 mothers, Mage = 38.73 ± 6.23 years and 227 children, Mage = 10.39 ± 4.96 years). In this study, 60.3% of children were underweight, 27.9% normal, 8.8% overweight, and 2.9% obese. Overall, 6.3% of children had smoking exposure and were overweight, whereas 1.4% were obese. Our results show that the relationship between maternal smoke exposure and body mass index (BMI) was non-significant (P > 0.05). Children whose mothers did smoke in pregnancy period were at low risk for obesity (odds ratio [OR] = 0.66, 95% CI: 0.07, 6.11) compared with children whose mothers never smoke. Conclusion: In this study, we found that the BMI of children not increased with maternal smoking exposure. In future, taking into consideration the health of mother and child, new studies should be performed to investigate the relationship between maternal or paternal smoking exposure and childhood overweight or obesity. Article History: Received: 11 May 2020 Accepted: 21 July 2020 e-Published: 22 Aug. 2020


Introduction
Obesity and smoking have become a public health crisis, and both are treated as a disease. Between 1975 and 2016, the obesity rate tripled in the world. 1 Researchers agree that too much caloric intake and too little exercise are both important factors in obesity prevalence, but studies suggest that toxic chemicals may also be a factor. 2,3 Obesity risk factors include diet, sedentary lifestyle, physical activity, psychological factors, genetic syndromes, some endocrine diseases, and smoking exposure. 4,5 This study evaluated the possible obesogenic effects of smoking exposure. Cigarette smoke is a source of over 4000 toxic compounds, some of which are anti-obesogenic (chromium and cadmium) and others are obesogenic (Benzo[a]pyrene and PM 2.5 ). Studies show that chromium and cadmium supplementation decrease body mass index (BMI) and fat. [6][7][8][9] Cigarette smoking causes polycyclic aromatic hydrocarbon (PAH) and particulate matter (PM) exposure. Experimental studies show that these substances may have an obesogenic effect. 2 In experimental studies, PAH exposure blocks lipolysis, resulting in increased BMI. Early lifetime exposure to PM causes mitochondrial detriment and raised accumulation of white adipose tissue relative to metabolically active brown adipose tissue. PM has estrogenic effects, and maternal exposure to environmental estrogens causes lead away obesity in animal bioassays. 10 Importantly, experimental study results have found that early exposure to nicotine might result in accelerated postnatal weight gain, as well as raised visceral adiposity. [10][11][12][13][14][15] The worldwide prevalence of overweight and obese children has increased. It is hard to assign the whole mechanism through which maternal smoking might result in raised offspring obesity. 16 Infants of mothers who had a smoke exposure in pregnancy period were lighter at birth than infants of non-smokers, but in adolescence, they had an increased risk of being in the highest decile of BMI. Evaluating epidemiological data supports a favorable relation between maternal smoking exposure and a raised risk of obese or overweight offsprings. 5,17,18 Over the past decade, there have been a large number of studies investigating the possible relationship between paternal/  12,19 However, in Turkey, no study has analyzed the possible obesogenic effects of cigarette exposure in childhood. The present study aims to fill the lack of scientific data on this subject.

Methods
A web-based survey using google documents was applied in Turkey over the Internet. This study was carried out with 379 woman and 379 children participants (n = 758). The present study was designed as a cross-sectional analysis of the survey. Mothers who were given consent, aged over 18 years old, and did not have an ongoing genetic and metabolic disease were included in this study. Also, children aged 2 to 18 years, whose parents gave consent, were included in the study. Subjects interested in participating received the questionnaire by mail, which collected information on socioeconomic position, demographic data, and several lifestyle parameters, including tobacco and alcohol consumption. The 31-question survey was administered to mothers. Mothers were asked whether they had been exposed to smoke before or after the pregnancy period. Each of these questions was supposed to be answered with "no" or "yes. " A 25-question survey was administered to children. In addition, age, sex, level of education, nutrition habits (fat, carbohydrate, protein), body weight, and height information were recorded in both of them. BMI, defined as the weight in kilograms divided by the square of the height in meters, was calculated and subjects were classified as underweight, normal, overweight, or obese according to the WHO criteria. 1

Statistical analysis
The data were analyzed using the statistical program Statistical Package for the Social Sciences (SPSS). Frequency and percentage analyses were used for analyzing participants' demographic characteristics and mean ± SD scores from the measurement tools. When the sampling error is ± 0.05, the sample volume of 384 is sufficient according to the situation where the volume of the main mass is one million. 20 In this study, we tried to reach a total sample volume of more than 384. The representation of the main volume of the sample volume was exceeded (n = 454). T-test analyses have been performed to compare two related groups in order to determine whether there is a statistically significant difference. Analysis of variance (ANOVA) is used to check if the means of two or more groups are significantly different from each other. A Chisquare test is used to analyze categorical data. A P value less than 0.05 was considered statistically significant. Odds ratios (OR) with 95% confidence interval (CI) were also measured to determine associations between the maternal smoke-exposed group and control group in the study population.

Results
This study was carried out from January to March 2020 with 379 woman and 379 child participants (n = 758). However, 304 (152 women, 152 children) subjects were excluded from the study because of missing data (age, height, weight). Finally, 227 women (M age = 38.73 ± 6.23) 18 years old or older, and 227 children (M age = 10.39 ± 4.96) who were ≥2 and ≤18 in Turkey were included. Maternal BMI was found at 19.10 ± 4.42. BMI from 454 participants (227 females and 227 children) are shown in Table 1, which shows that 11.3% of children were overweight or obese. Baseline characteristics of mothers are shown in Table  2. Results show that the relationship between maternal income and maternal smoking is statistically significant (P = 0.004). The relationship between maternal education and smoking is also statistically significant (P = 0.007). The participants were asked if they thought their child was overweight/obese, and if they thought their child gained weight despite a regular/balanced diet. In addition, we asked the mothers that is their child was weight gain despite a regular/balanced diet. We assessed there was no association (P > 0.05). Mother's views on their children's BMI and diet was shown in Table 3. Most mothers (77.4%) thought that their child was overweight or obese. In the present study, 60.3% of children were underweight, 27.9% normal, 8.8% overweight, and 2.9% obese. Overall, 6.3% of children had smoking exposure and were overweight, whereas 1.4% were obese. Characteristics of offspring, according to maternal smoking, are shown in Table 4. According to the results, the association of smoking habits and the children's BMI was statistically non-significant (P = 0.372). The association between physical activity and the mother smoking was statistically significant (P = 0.03). The association between television watching of children and mother smoking was statistically significant (P = 0.016). Table 5 shows the prevalence of maternal smoking and mean BMI in the offspring. The relationship between maternal smoking before pregnancy, during pregnancy, and the postnatal period, and BMI of the child was statistically non-significant (P > 0.05). According to the results, children whose mothers smoked during pregnancy had an elevated risk for obesity (pooled adjusted OR = 0.66, 95% CI: 0.073, 6.111) compared with children whose mothers did not smoke during pregnancy (Table  6). We evaluated the relation between maternal cigarette smoking and the child's BMI. The most valuable result of this study is that there were no statistical differences found   between maternal smoking and BMI (P > 0.05).

Discussion
Although smokers tend to have a lower BMI than nonsmokers, smoking might support abdominal body fat accumulation. However, no population-based studies have evaluated the association between smoking and body fat composition. 21 Results showed that the relation between cigarettes smoked per day and BMI was nonsignificant. Besides, over the past decade, there have been a large number of studies investigating the possible relationship between smoking and overweight or obese outcomes. 12,19,22 The population prevalence of overweight and obese children has raised. There are limited studies about maternal/paternal smoke exposure and childhood obesity. Infants of mothers who smoked during pregnancy period had lower birth weight in comparison with the infants of non-smokers, but during adolescence, they had a raised risk of being in the highest decile of BMI. 16 Last epidemiological findings support a favorable relation between maternal smoking exposure and raised risk of obese or overweight offspring. 5,17 Studies report a relationship between maternal smoking in pregnancy period and risk of overweight children at least. Analyzes show that the early influence of maternal smoking on the prevalence of overweight children at age 2 or 3 years is high-risk. 23,24 Interestingly, smoking by adolescents was not related to weight, height, or head circumference of the subjects. 25 However, tobacco smoking causes lower BMI among current smokers, 26 although Lv et al reported that tobacco smoking could be an important risk factor for obesity. 22 Also, epidemiological and experimental research (83 in humans and 18 in animals) related to smoking exposure found a positive association between obesity at any age and exposure. 5 A considerable amount of studies indicate that smoking and obesity are related to adverse pregnancy outcomes, and especially smoking during pregnancy has a relationship with childhood obesity. [27][28][29] Results show that the prevalence of overweight and obese offspring was greater for those whose mothers had smoked in pregnancy period than those whose mothers had never smoked. Obesity is also significantly related to smoking between 28 and 32 weeks of gestation, with some indication of a dose-response. Researchers suggest that maternal smoking during pregnancy not only directly causes childhood obesity but also affects adolescent obesity. 30 In this study, we present the first comprehensive study regarding the impact of maternal cigarette smoking on BMI compared with healthy non-smoking mothers in Turkey. Children whose mothers smoked in pregnancy period had a low risk for obesity (pooled adjusted OR = 0.66, 95% CI: 0.07, 6.11) compared with children whose mothers did not smoke. Our findings suggest that smoking exposure in pregnancy period is not a risk factor for being overweight in childhood. According to some views about smoking and obesity, results might support the hypothesis of "fetal origin of adult disease", but the risk of being overweight related with smoking during pregnancy period was independent of intrauterine growth retardation, and may thus be based on particular effects of cigarette smoke. 23,27 Conclusion In conclusion, evaluating recent epidemiological data supports a prominent relation between maternal smoking and an increased risk of obese or overweight children. Therefore, prominent findings regarding smoking could indicate a candidate for a new obesogen. Active or passive exposure to smoke is also a significant source of toxic chemical exposure. People should be encouraged never to take up smoking. Moreover, the worldwide prevalence of childhood obesity has raised and considering the health of mother and child, new studies should investigate the relationship between maternal or paternal smoking exposure and childhood weight or obesity to determine the detailed mechanism.

What is current knowledge?
• Childhood overweight or obesity could be related with maternal smoking during pregnancy period.

What is new here?
• Smoking exposure in pregnancy period is not a risk factor for being overweight/obesity in childhood.