Basic information
The flow of the subjects was seen in Table 1. The average age of participants was 13.31 ± 2.98 years old (Table 2). A total of 310 students were diagnosed with MAFLD, for a prevalence of 23.83%. Looking separately by age group, 22.7% of children and 24.43% of the adolescents were diagnosed with MAFLD.
Risk factors for MAFLD
Results of the bivariate analyses showed no significant differences between the MAFLD groups in terms of age. However, in both age groups and the combined sample, anthropometric measures were significantly higher in the MAFLD group than in the non-MAFLD group (p<0.001 for all comparisons). Logistic regression analyses revealed height, weight, BMI, waist circumference, and hip circumference as significant risk factors for MAFLD in children and adolescents; results for age and learning stage were not significant. However, liver stiffness in the MAFLD group was significantly higher (p<0.001) than that in the non-MAFLD group; this result was found for adolescents and the combined sample but was not found for children (Tables 3 and 4).
BMI and Fatty liver
A total of 345 students of the 1,301 study subjects were overweight (BMI ≥24); 224 of the overweight students had varying degrees of fatty liver. The overall prevalence rate was 64.93% (95% CI: 0.599-0.700); 9.00% (95% CI: 0.072-0.108) of the non-overweight (BMI<24) students had MAFLD (p<0.001). In addition, the chi-square tests showed that the overweight group had a significantly higher prevalence of mild to moderate severe fatty liver than the non-overweight group. The overweight group also had significantly higher values of age, height, weight, waist and hip circumference, WHR, FAP, and liver stiffness (p<0.001). There were 203 boys and 142 girls among the overweight students, with prevalence rates of 68.97% (95% CI: 0.625-0.754) and 59.15% (95% CI: 0.510-0.673), respectively; these differences were not significant (p<0.001).
The prevalence of fatty liver among obese students was quite high—90.54% (134 of the 148 students, 95% CI: 0.858–0.953). Among them, the proportions of boys and girls with fatty liver were 93.33% (95% CI: 0.881–0.986) and 86.21% (95% CI: 0.771-0.954), respectively. These prevalence was not significantly different (p>0.05) (Table 5). The prevalence of overweight, obesity, and abdominal obesity was significantly higher in the MAFLD group (p<0.001 for all comparisons) (Table 3). After stratification by sex and age, the prevalence of MAFLD in both boys and girls increased with BMI; this pattern was seen for both age groups (Figure 1).
Grade level and MAFLD
There were 395 elementary school students, 427 middle school students, and 479 high school students in the study, among whom 91, 107, and 112, respectively, were diagnosed with fatty liver. The overall prevalence rate was 23.8%, with grade-level results of 23.04% (95% CI: 0.189-0.272), 25.06% (95% CI: 0.209-0.292), and 23.38% (95% CI: 0.196-0.272), respectively. These differences were not statistically significant (p>0.05). Most of the elementary school students with fatty liver had a mild level, accounting for 15.19% of their cases. The proportion of junior high school students with moderate fatty liver was the highest. Nonetheless, there was no significant difference in the prevalence of moderate fatty liver among the three grades (p=0.023). The prevalence of severe fatty liver increased significantly with educational level (p<0.001). There were no significant differences between junior and senior high school students in FAP or liver stiffness. However, both groups were significantly higher on these measures than were the elementary school students (p<0.001). In addition, the value of other anthropometric factors and clinical measurements increased significantly with improvement of academic level (p<0.001 for all comparisons) (Table 6).
Sex and MAFLD
The 1,301 study subjects included 625 boys and 676 girls. Among the boys, 182 were diagnosed with fatty liver (29.12%; 95% CI: 0.255–0.327); the 128 girls with fatty liver represented a prevalence of 18.9% (95% CI: 0.160–0.219). The overall prevalence for boys was significantly higher than that of girls (p<0.001), which mainly reflected the differing prevalence of severe fatty liver. There was no significant difference in age between the two groups. However, the values of height, weight, BMI, waist circumference, hip circumference, WHR, FAP (p<0.001 for all comparisons), and liver stiffness (p<0.01) were significantly higher in boys (Table 7). The overall prevalence of fatty liver increased with age; for instance, the prevalence of fatty liver in students younger than 8 years old was 2.38%, while the prevalence in students older than 17 years old was 24.76%. After stratification by sex and age, only the 13-14 age group showed a significantly higher prevalence among boys than among girls (p<0.001). Similarly, after stratification by gender and education, the prevalence of fatty liver in the elementary and middle schools, but not high schools, was significantly higher in boys than in girls (p<0.05) (Table 8).
Questionnaire
The questionnaire was valid for 117 of the 123 students. Tables 9 and 10 present the comparisons of the questionnaire factors between students with and without fatty liver. The basic information of children is consistent with that shown in the epidemiological survey. Fathers of children in the MAFLD group were more likely to have an educational level of high school or lower (p<0.05). Regarding exercise habits, the proportion of students in the MAFLD group who did not exercise or who had poor grade was significantly higher. In terms of eating habits, the students in the MAFLD group ate breakfast less frequently than those in the non-MAFLD group (p<0.05) but had a higher frequency of consuming fast food and snacks (p<0.05). Furthermore, the ratio of eating carefully and slowly was higher in the non-MAFLD group. Parents of adolescents with MAFLD also had higher BMI. Similar to children, more students ate breakfast every day in non-MAFLD group (p<0.05). Parents of adolescents with MAFLD had less knowledge of nutrition and health. Finally, no significant differences were found between the two groups in basic conditions of birth, recreation, and learning (p>0.05).