The Relationship Between Sleep Quality with Body Mass Index and Blood Lipid Level in Adolescents

Sleep is one of the fundamental needs of human and one of the most important circadian cycles [1]. Any kind of disorder in its natural process can reduce efficiency of individuals in addition to create mental problems [2]. In adolescents, changes in social environments can make some changes in their sleep pattern when their growth and evolution is depended on enough sleep for health [3]. Sleeping, along with food habits, physical activity and smoking have been considered as risk factors of cardiovascular diseases [4]. Futuristic and retrospective studies have shown that root of risk factors is in cardiovascular diseases, diabetes, hypertension, Dyslipidemia and overweight, which can be affected by factors in relation with lifestyle in childhood and adolescence [5,6]. Dyslipidemia is the first step of beginning of Atherosclerosis in cardiovascular diseases [7]. In a study on heart, Bogalusa has demonstrated that increase in blood lipids in childhood and adolescence is correlated to increased risk of atherosclerosis and cardiovascular diseases in adulthood [7]. In the study of Latifi in Ahvaz City, prevalence of hyperlipidemia has been equal to 29.9% in 10-19 years old adolescents based on suggestion of US Academy for Children [8]. Received: September 05, 2019 Published: September 10, 2019

The statistics have been higher than American 12-19 years old adolescents (20.3%) [9]. In addition to blood lipid disorders, obesity is also one of the most important risk factors of coronary arteries [3]. Adolescence is an important age for development of obesity [10]. During 2 past weeks, prevalence of obesity in children and adolescents has been significantly increased across the world [11], so that the value has reached to 31.8% by 2010 [12] and the value is about 30% in Asian countries [13]. As adolescents of the current world form adult population of future, future adults would be more successful [14]. Two important health problems of adolescents presented by American Medical Association for Children leading to diseases in adulthood include obesity and hyperlipidemia that can enhance risk of cardiovascular diseases in adulthood [3].
Similar studies in field of investigating the relationship between sleep quality and blood lipid with BMI have been conducted in countries such as America [15], Brazil [16], Switzerland [17], New Zealand [18], China [19] and Norway [20] with different results.
In some studies, sleep has been in significant correlation with MBI and blood lipid [11,15,19,20]. In other studies, no correlation was observed [16,[21][22][23]. In this regard, study of Azadbakht et al. showed that there is significant correlation between reduction of sleep time and increase in LDL and triglyceride; although there was no correlation between short time of sleep and increased BMI [24]. According to different results in different studies, scholars have decided to investigate the relationship between sleep quality with BMI and blood lipid in Ahvaz. Through reflecting the results of these studies to relevant authorities to use required strategies to meet relevant problems of wrong lifestyles of today's adolescents, implementation of such models can optimize effective costs for medical systems and institutes.

Methods
In this descriptive-analytical study, statistical population consists of all adolescents of 15-20 years old in Ahvaz City. 310 adolescents were selected using cluster sampling. From 25 health centers, 6 centers (2 centers in west and 4 in east) were selected randomly. After getting permission of Research Deputy of Medical University of Jundishapur of Ahvaz/Iran, the author entered to determined health centers and through investigating records of families with adolescents in 15-20 years old, several records were selected randomly. They were referred as cluster head and then, the families to level of 40 families were invited to participate in this study in case of having adolescents and agreed to be present in this project. In regard with details and goals of the study and data collection, data and written consent was received from the parents or adolescents based on volunteer participation in this study. Also, the participants were asked to be in fast 1 night before presence in health centers (12hrs before). After presence of adolescents in determined health centers, two questionnaires were fulfilled using interview by the author.

Results
In this study, 310 adolescents in age range of 15-20 years old are studied and 52.3% of them were male. Mean age range of participants has been equal to 17.46±1.5. Half of adolescents were in age range of 15-17 and half of them in age range of 18-20. Among adolescents, 11.3% had high triglyceride level; 5.8% had high cholesterol; 30% had abnormal HDL and 4.5% had increased LDL (Table 1). In order to investigate sleep quality with BMI and lipid profile, chi square test is used and to compare mean value of sleep quality between different levels of BMI and lipid profile, Kruskal-Wallis test is used. Kruskal-Wallis test was used to compare mean value of sleep quality in different levels of LDL and significant difference was observed among 3 groups of studied samples (p=0.048). Through comparing mean values of the 3 groups using Mann Whitney test, significant difference was observed (p=0.013) ( Table 2). However, significant correlation was observed between lipoprotein and low density and sleep quality (pvalue=0.022) ( Table 3). In boys and girls, separated for adolescence, significant correlation was observed in girls only between BMI and sleep quality (pvalue=0.041) ( Table 4).    been respectively obtained to 6.5, 6.2, 5.65 and 45 [29]. Prevalence of triglyceride and increased LDL is more than Tehran's adolescents and the differences can indicate racial and ethnical differences and lifestyles in these two cities. Moreover, time interval between the two variables can be reason for these differences. In this study, there was no significant correlation between sleep quality and BMI; although it was observed that in girls in end of adolescence, more numbers of obese or overweighed individuals had experienced inadequate sleep.
Obtained results from different studies in this filed are different from each other. In study of Yeelmaz in Turkey showed negative correlation between sleep and BMI [30]. In some similar studies like study of Mota, no significant correlation was observed between sleep quality and BMI [21,22] In studies of Gangovich and Azadbakht, contrary to this study, significant correlation was observed between sleep duration and LDL among girls [15,24]. According to the obtained data, it could be mentioned that the correlation between sleep and LDL is depended on gender. In study of Ray Lopez in European countries, no significant correlation was observed between sleep duration and dyslipidemia [37], which is in consistence with the present study.
In China, among adolescents of Secondary School, those with long sleep duration had lower LDL and significant correlation was observed between LDL and sleeping duration; although no significant correlation was observed between other profiles of lipid and sleep duration [19]. Study of Azadbakht in Iran showed that cholesterol level is in positive correlation with sleep duration among boys and long sleeping time can increase cholesterol level.
Moreover, boys with sleep time more than 8hrs showed higher level of HDL [24]. In Korea, people with sleeping hours more than 10hrs had higher level of triglyceride and the correlations in boys were clearer than girls [35]. In study of Sung on obese adolescents, it was found that increase in sleep duration is in significant correlation with reduction of HDL and increase in triglyceride [23], which is not in consistence with results of this study. It seems that other factors such as environmental factors play more effective role in regard with determining blood lipid level, BMI and sleep quality.
It is suggested to measure effect of environmental factors on these variables in further studies. One limitation of this study is crosssectional nature of the study that lack of causal relationship can be derived from it. Hence, it is suggested to measure the correlation between sleep quality with blood lipid and BMI in long-term form (Cohort).

Conclusion
Obtained results from this study in relation with determining the correlation between sleep quality with BMI and blood lipid level in adolescents showed no significant correlation between sleep quality and other variables. However, sleep quality in girls in end of adolescence is in correlation with BMI and with LDL in boys. In this study, it was observed that about half of adolescents suffer at least from one lipid disorder and inadequate sleep quality and about 1 sixth of adolescents suffer from overweight and obesity. According to obtained results from this study, it seems that adolescents should be studied in terms of sleep quality and cardiovascular factors, so that their emergence can be reduces and they can be prevented through recognizing factors affecting the disorders.