1. Background
Over the last decades, life-style has been changed dramatically including sedentary behaviors and unhealthy diet leading to a sharp rise in the incidence of obesity affecting children and adolescents as well (1). The prevalence of childhood obesity has been rising globally and has become a major childhood health problem in many countries causing several subsequent medical conditions including cardiovascular disease, Type 2 diabetes, hypertension, hyperlipidemia, and non-alcoholic fatty liver disease (2, 3).
Today, with a prevalence of 20% to 70%, the non-alcoholic fatty liver disease (NAFLD) is considered as the most common liver disease during childhood with a rapid increasing number (4-6). The NAFLD is defined based on paraclinical investigations due to lack of symptoms including abdominal ultrasonography and liver function tests (7). Liver steatosis, at abdominal ultrasonography, beside a mild elevation of liver function tests (including serum glutamic-oxaloacetic transaminase and glutamic pyruvic transaminase), are usually the main criteria of NAFLD. Occurrence of NAFLD during childhood affects the quality of life and these patients suffer higher level of emotional and behavioral problems (8). In addition, NAFLD causes several serious comorbidities (6).
There are several articles concerning the prevalence of NAFLD during childhood in Iranian children reporting a prevalence of 7% - 86% with large geographic variation in distribution of it (9-13). Based on search, there is no new report regarding the prevalence of NAFLD in the south east of Iran. Considering the dynamic of changes in human behaviors as well as need for up to date data, this study aimed to assess the prevalence of fatty liver in obese and overweight children aged 12 - 18 years in Birjand city.
2. Methods
2.1. Population of Study
This is a cross-sectional study conducted on 200 adolescents aged 12 to 18 years who are overweight and obese in Birjand, the capital of South Khorasan, south east of Iran. The inclusion criteria was the body mass index (BMI) of 85% or higher percentile (according to the Centers for Disease Control and Prevention, CDC, chart in terms of male and female gender). The exclusion criteria included known thyroid dysfunction (hypothyroidism and hypoparathyroidism), diabetes and Cushing’s syndrome, as well as chronic consumption of any kind of drugs, such as corticosteroids, weight reducing or increasing agents, a history of alcoholism, and hepatitis caused by other factors (hereditary diseases, viruses, etc.). In multi-stage sampling, Birjand was first divided into five geographical regions (west, east, south, north, and center), and two schools were selected from each region; i.e. a total of 10 schools were selected from the entire city, and the number of girls’ and boys’ schools was the same (five boys’ and five girls’ schools). After determining the schools, we randomly selected and examined the adolescents who were obese or overweight from different grades in each school. The weight of the subjects was measured and recorded using a German digital Seca scale, while they were not wearing shoes and had the least amount clothes on. The height of the subjects was measured in meter twice, as they were standing without shoes. The BMI was then calculated by dividing the weight (in kilograms) into height squared (in meters), and the BMI with a percentile of 85 - 94 was considered as overweight with 95 ≤ considered as obese.
2.2. Methods
The protocol of the study was approved by the Ethics Committee of Birjand University of Medical Sciences. Written informed consent was obtained from participants and their parents. There are different imaging and laboratory measurements in order to diagnose the presence of fatty liver, including noninvasive assessment of parenchyma of liver using abdominal ultrasonography with an appropriate sensitivity and specificity (14, 15). Therefore, to determine the presence of fatty liver in adolescents who were obese or overweight an abdominal ultrasound was performed by a radiologist after six hours of fasting. The ultrasound method was as follows: in order to calculate the liver span along the midclavicular line, the superior and inferior limits of the liver were determined and the distance was measured with a regular fixed ruler. The liver parenchyma was then evaluated using two subcostal windows in the right upper quadrant (RUQ) and at the coronal section along the Axilary lines. To identify the presence of fatty liver, an increase in the echogenicity of liver parenchyma was determined at the level of fat echo and the detection of portal and hepatic veins. The ultrasound criteria for fatty liver severity include:
Grade 1 (mild): Echogenicity of the liver increases slightly, and the limits of diaphragm and intra-hepatic arteries are normal.
Grade 2 (moderate): Echogenicity of the liver increases moderately, and the limits of diaphragm and intra-hepatic arteries are slightly faded.
Grade 3 (severe): Echogenicity of the liver increases severely, and the limits of diaphragm and intra-hepatic arteries and the posterior part of the right lobe of the liver are faded or hardly observed (16).
Then in second stage , 5 mL of venous blood samples were taken for each subject that had NAFLD for laboratory tests including TG, cholestrol, HDL, LDL, ALT, AST, FBS, CRP, insulin, PLT, uric acid, and 25 OH Vitamin D .The blood samples were sent to the reference laboratory affiliated to Birjand University of Medical Sciences.
2.3. Statistical Analyzing
The data on demographic and clinical observations were analyzed using the SPSS version 22. The descriptive statistical methods including measures of central tendency, dispersion, and frequency distribution were used to describe the subjects’ data. The chi-square test was also used to determine the difference in frequencies of fatty groups and the groups under study as well as determine the relationship between age groups and obesity and overweight in adolescents aged 12 to 18 years. We used the Fischer’s exact test to determine the relationship between the prevalence of fatty liver in the age groups. To study the effects of age, sex, and BMI on the prevalence of non-alcoholic fatty liver, the forward multivariate logistic regression (conditional) was used based on selection of possible factors if P < 0.2 in univariate analysis. In all tests, P ≤ 0.05 was considered as the significant level.
3. Results
A total of 108 adolescents who were overweight and or obese suffered from NAFLD (i.e. prevalence of this disease was 54%, 95% CI 47 - 61). The frequency of NAFLD in boys and girls was 69.8% and 42.1%, respectively (P < 0.001). There was a considerable number of NAFLD in adolescents aged 12 - 13 years and also obese individuals (for both P < 0.001) (Table 1). Of the 108 adolescents with NAFLD, grade I, II, and III with 83.3%, 14.8%, and 1.9% had the highest frequency, respectively. Table 2 presents biochemical parameters of blood in adolescents with NAFLD.
Table 1.Comparison of Relative Frequency of NAFLD in Overweight and Obese Children in Terms of Gender, Age, and Body Mass Indexa
| Variables | Inflicted with Fatty Liver | P Value | Chi-Square | |
|---|---|---|---|---|
| No | Yes | |||
| Gender | < 0.001 | χ2 = 15.10 | ||
| Male | 26 (30.2) | 60 (69.8) | ||
| Female | 66 (57.9) | 48 (42.1) | ||
| Age group, y | < 0.001 | χ2 = 25.59 | ||
| 12 - 13 | 17 (23.3) | 56 (76.7) | ||
| 14 - 15 | 45 (64.3) | 25 (35.7) | ||
| 16 - 18 | 30 (52.6) | 27 (47.4) | ||
| Body mass index, kg/m2 | < 0.001 | χ2 = 25.59 | ||
| Overweight | 58 (64.4) | 32 (35.6) | ||
| Obese | 34 (30.9) | 76 (49.1) | ||
a Values are expressed as No. (%).
Table 2.Biochemical Parameters of Blood in Patients with Fatty Liver
| Biochemical Parameters of Blood | Mean ± Standard Deviation | Minimum Value | Maximum Value |
|---|---|---|---|
| WBC | 8.24 ± 2.07 | 4.80 | 15.50 |
| HB | 14.91 ± 1.34 | 8.40 | 18.80 |
| PLT | 302.03 ± 71.41 | 184 | 577 |
| FBS (mg/dL) | 92.74 ± 7.04 | 75 | 108 |
| Uric acid (mg/dL) | 5.65 ± 1.40 | 2.90 | 9.40 |
| Chol (mg/dL) | 162.47 ± 30.21 | 95 | 250 |
| TG (mg/dL) | 143.40 ± 63.59 | 41 | 340 |
| HDL-c (mg/dL) | 38.28 ± 6.89 | 19 | 63 |
| LDL-c (mg/dL) | 99.60 ± 26.54 | 46 | 196 |
| Insulin | 24.72 ± 10.71 | 4.97 | 62.70 |
| Alb | 4.54 ± 0.32 | 3.80 | 6.10 |
| AST (IU/mL), median | 24.63 ± 7.32 | 13 | 46 |
| ALT (IU/mL), median | 28.42 ± 14.09 | 7 | 84 |
| ALK | 220.64 ± 97.40 | 53 | 663 |
| CRP | 2.26 ± 2.37 | 0.10 | 13 |
| Vit D | 10.52 ± 5.94 | 2.10 | 28.40 |
Table 3 shows results of the Logistic regression. There was a significant relationship between age, sex, and BMI and the prevalence of non-alcoholic fatty liver (P < 0.001). The results clearly indicate the high vulnerability of low-aged adolescents from non-alcoholic fatty liver compared to adults (P < 0.001). In addition, the BMI of obese individuals increased the risk of non-alcoholic fatty liver 3.5 times more than that of overweight people, which could well indicate the role of obesity in the prevalence of non-alcoholic fatty liver (OR = 3.57, 95% CI: 1.87 - 6.81). Furthermore, studying the relationship between the prevalence of fatty liver in sex groups clearly showed that the risk of non-alcoholic fatty liver in men was higher than in women, and being a girl significantly reduced their risk of the disease (OR girl = 0.21, 95% CI: 0.10 - 0.43).
Table 3.Logistic Regression Results Between Prevalence of NAFLD and Age, Sex, and Body Mass Index
| Groups | OR | 95% CI | P Value |
|---|---|---|---|
| Age | 0.692 | 0.579 - 0.828 | < 0.001 |
| Gender (girls) | 0.214 | 0.105 - 0.433 | < 0.001 |
| BMI (obese) | 3.57 | 1.87 - 6.81 | < 0.001 |
4. Discussion
The present study aimed to assess the prevalence of non-alcoholic fatty liver in obese and overweight adolescents (12 to 18 years) and describe its clinical features. The overall prevalence of NAFLD in obese and overweight adolescents in this study was 54%. Similarly, in a study by Fattahi et al. (17), the NAFLD was reported in approximately half of the patients suffering from metabolic syndrome, where obesity and hypertriglyceridemia are two of its criteria (comparing 25.7% in the general population). The present study clearly shows that obesity at an early life increased the risk of non-alcoholic fatty liver by 3.5 times. Accordingly, Jimenez-Rivera et al. (2), reported that adolescents with NAFLD were at a greater risk of liver-associated disease and a significantly shorter survival than those of similar sex and age. Previous studies by Kazemi et al. (18), Taghavi Ardakani et al. (12), Abangah et al. (19), and Adibi et al. (20), confirmed the findings.
In addition, our study showed that being male was predominantly affected by the NAFLD, similar to the results of the studies by Di Sessa et al. (21), Schwimmer et al. (22), and Tominaga et al. (23), yet opposed to the findings of Fu et al. (24), and Adibi et al. (20). It seems that a difference in sex-hormones and presence of high estrogen levels in younger-aged women during pre-menopause period protects them from NAFLD (25). Anti-oxidative effects of estrogen have been proven leading to inhibition of development of fibers and proliferation of hepatic stellate cell (26, 27). Beside the absence of anti-oxidative effects of estrogen, higher speed of accumulation of visceral adipose tissue in obese men increase the susceptibility of men to NAFLD (28).
Regarding age, the relative prevalence of NAFLD in adolescents aged 12 - 13 years was 76.7%, which is due to the fact that a higher percent of 12 - 13 year-old adolescents were obese. Of the 108 adolescents with NAFLD, 90 (83.3%) had grade 1 NAFLD, 16 (14.8%) had grade 2, and two (1.9%) had grade 3 NAFLD, with grade 1 as the dominant type of NAFLD; this finding is similar to those of Di Sessa et al. (21), Kazemi et al. (18), and Taghavi Ardakani et al. (12).
In this study, various metabolic disorders were found in the adolescents with NAFLD including increased blood sugar and lipid blood levels. It seems that NAFLD is a component of metabolic syndrome.
Another noteworthy finding in this study was that 100% of the adolescents with NAFLD had vitamin D deficiency. Vitamin D deficiency stands as a risk factor for metabolic syndrome; yet interestingly, both are of a high prevalence in the Iranian population (29, 30). Vitamin D holds anti-inflammatory and regulatory properties. It can reduce insulin resistance and increase insulin secretion.
One of the limitations of this study was the technique employed, although the same method, i.e., liver ultrasonography was applied in most studies (16). Nonetheless, the golden diagnostic standard is biopsy, which is invasive. Other imaging techniques that have been employed comprise of magnetic resonance (MR) and computed tomography (CT). Whilst arguably the most precise test to evaluate liver fatty infiltration, MR is nevertheless costly and at times inaccessible in many situations (31, 32). CT, which is more accurate when diagnosing fatty liver, is usually accompanied by radiation exposure; hence, it is not generally applied. Moreover, to quantify the amount of fat and water in the liver, spectroscopy has proven more accurate than the conventional MR images (32, 33). Nonetheless, whereas such tests are accurate, there are limiting parameters including cost and accessibility. Meanwhile, transient elastography is employed as a non-invasive measure that evaluates the extent of fibrosis in chronic liver diseases such as NAFLD (2).
4.1. Conclusions
The results of this study showed that obesity and being male were associated with an increased risk of non-alcoholic fatty liver and, on the other hand, a low BMI and being female significantly reduced it. However, given the inadequacy of causal studies in this area, the generalization of the results of this study should be done with caution. In addition, further studies in this regard can lead to finding out the role of the factors affecting the prevalence of obesity and non-alcoholic fatty liver in adolescents, and implementing preventive and interventional programs in lifestyle and diets that can help reduce the burden of non-alcoholic fatty liver disease in adolescents and therefore, in adults.
