Discovering the differences between rural and urban regions in MAFLD burden can facilitate public health policy-makers in recognizing, monitoring, and prioritizing potential concerns for complication prevention. In our large population-based, prospective, cross-sectional study of Guangdong Province, representative of the general population of China, we identified a higher overall prevalence of MAFLD than that reported in the recent meta-analysis, and further comparison of the differences in metabolic abnormalities, liver injuries, and hepatic fibrosis between rural and urban districts revealed the unneglected disease burden. We found no significant difference in the prevalence of MAFLD between rural and urban individuals, although rural individuals had more severe fatty liver-related hepatic fibrosis than urban individuals. We also found that the prevalence of MAFLD and related hepatic fibrosis had little association with the economy as evaluated by the GDP per capita but were more closely related to lifestyle and dietary habits.
As reported in the literature, the prevalence of MAFLD is significantly higher in economically developed regions than in developing or poor regions both globally and within the China mainland [4]. However, our study found no significant correlation between the per capita GDP and the prevalence of MAFLD across regions, and it can be inferred that economic development does not directly affect the prevalence of MAFLD but indirectly increases the risk of NAFLD by concomitantly changing the diet and lifestyle habits of the residents. It is suggested that economic development, urbanization and environmental changes play crucial roles in the occurrence of MAFLD and related metabolic disorders [13]. A previous meta-analysis of NAFLD prevalence in mainland China included only two studies from rural populations with 7656 participants. The findings documented that the prevalence of MAFLD according to ultrasound screening was higher in urban than in rural settings (30.43% vs. 17.01%), but the difference was not significant (p = 0.128)[4]. The reported sensitivity of conventional abdominal ultrasound for discriminating mild steatosis is 55.3–66.6%[14–15]. Therefore, the true prevalence of undiagnosed fatty liver may have been underestimated due to the lack of sensitivity of ultrasound for distinguishing mild steatosis. When using the CAP, the pooled sensitivity of detecting mild steatosis could be as high as 84% according to a recently published meta-analysis of 61 studies and 10537 included patients[11]. In the present study, 38.0% of the rural cases were identified as MAFLD, which is almost two times that reported in a previous study. Therefore, the true ratio of undiagnosed MAFLD might have been underestimated. Even accounting for disparities in diagnostic approaches, our results document a substantial increase in the prevalence of MAFLD or NAFLD, which is contradictory to the higher prevalence of MAFLD among urban than among rural residents that has been reported in other countries throughout the world[5, 16, 17].
The rapid growth in GDP and alterations in lifestyles have been considered the major drivers of the epidemiological surge of NAFLD in China. During this process, urbanization has been considered the cause of the accelerated MAFLD epidemic. Indeed, our study also showed that the prevalence of MAFLD in rural areas, even at a lower level of urbanization, was significantly unexpectedly higher than that in urban areas, suggesting that urbanization itself might not independently or directly explain the increasing prevalence of MAFLD in China.
Since 2020, the concept of MAFLD has been raised, and metabolic dysfunction has been emphasized in disease establishment [18]. Our study first adopted these criteria in rural population screening[19]. More importantly, our study showed that among different stratifications, including age and sex, there was little difference in steatosis degree between rural and urban individuals, but rural areas presented a higher proportion of advanced fibrosis (≥ F3) than urban areas in the overall, overweight/obesity and lean/normal weight subgroups and among gender stratifications. Previous studies in China and other East Asian countries have reported that rural residents suffer less from MAFLD and hepatic metabolic disorders than urban residents, and that rural living is a protective factor [20–22]. However, after 5 years, the lifestyle and dietary habits of both Chinese urban and rural residents have tremendously changed. Our study found that in both areas, BMI, waist-to-hip ratio and metabolic disorder severity had a great impact on the risk of MAFLD, illustrating the increased prevalence of obesity. One hypothesis for explaining this opposing finding might be that lifestyle alterations, especially regarding diet, have been much more easily accepted by rural residents than urbanization[23]. Both urban and rural residents would be more likely to share the fashioning dietary habits that to pursue delicious food characterized by increased caloric, sugar and fat intakes. Moreover, as a developed area of China with greater awareness of the damage caused by MAFLD, urban residents have a relatively high knowledge of MAFLD and will spontaneously adjust some lifestyle and dietary patterns [24]. A lack of awareness of MAFLD may be one of the reasons why the BMI and waist-to-hip ratio of urban residents were lower and fibrosis severity was milder than those of rural residents in our study. Excessive sedentary time and lack of physical activity are important factors that increase the risk of MAFLD [25], but in our study, we only found this phenomenon in urban populations. Supported by the analysis of the relative contributions of lifestyle factors to MAFLD prevalence, unhealthy eating behaviors such as midnight snacks just before sleep and dining out often were independent risk factors for MAFLD among both rural and urban individuals. These findings provide an indication of the lack of preparedness for prevention in rural China. Targeting unhealthy lifestyles would be an effective intervention for addressing this problem.
Indeed, mainland China and Guangdong Province share the same development pattern and process—the economic development of urban and rural areas is not balanced. As a result, we can infer from our study data that when poverty was eliminated in rural areas of mainland China, the dietary habits of rural residents changed tremendously and became closer to the Western dietary pattern. This is one of the most important MAFLD risk factors hidden behind economic development. Fifteen years ago, a population-based survey that recruited 3543 participants from Guangdong Province reported a large gap in the prevalence of fatty liver disease between rural and urban areas (12.9% vs 23.0%, p < 0.001) [26]. From the increase in the overall prevalence of MAFLD in Guangdong Province and the changes in the prevalence of MAFLD in urban and rural areas, we can speculate that mainland China is facing the same problem—the challenge of MAFLD prevention and management in rural areas. Another problem caused by the rising prevalence of fatty liver in rural areas is that the risk of concomitant metabolic complications, such as diabetes, hypertension, hyperlipidemia, and cardiovascular and cerebrovascular diseases, will be greatly increased [13]. To slow this trend, a universal healthcare system is necessary for Chinese rural residents in the near future.
Our study had some limitations. The study was cross-sectional in design and could not determine the incidence of MAFLD. Our study does not contain any genetic data, but over 95% of the resident population in Guangdong Province is Han Chinese, which means that the individuals recruited were highly homogenous in genetic background. However, China is a vast country with a multiethnic population, and future investigations must take these factors into account.
In conclusion, we provided data on the presence and burden of MAFLD that encourage the urgent prioritization of prevention improvement in rural regions of China. The strikingly high prevalence and fibrosis severity of MAFLD in rural areas and the shared unhealthy lifestyle risk factors of both rural and urban individuals indicate that lifestyle changes markedly instead of urbanization itself might drive the surging epidemic of MAFLD in China. These findings suggest a continued need to develop a rural-targeted, evidence-based strategy to prevent morbidity and mortality associated with MAFLD.