Characteristics of gender differences and age in nonalcoholic steatohepatitis with regard to the complications of lifestyle-related disease, fat distribution, adipocytokines and SNPs

Epidemiology of non-alcoholic fatty liver disease and non-alcoholic steatohepatitis in Japan: A focused literature review

Non‐alcoholic fatty liver disease (NAFLD) and non‐alcoholic steatohepatitis (NASH) represent a growing unmet medical need and an increasingly prevalent cause of cirrhosis, hepatocellular carcinoma (HCC), and death in Japan. The aim of this review was to characterize the epidemiology of NAFLD and NASH in Japan. An English and Japanese literature search was conducted in PubMed, Embase, and ICHUSHI Web, identifying 6553 studies, 67 of which were included. Prevalence of NAFLD in the Japanese population rose from the early 1990s (12.6–12.9%) to the early 2000s (24.6–34.7% of the population). Japanese NASH prevalence is estimated to be 1.9–2.7%. NAFLD and NASH are more common among males than females; however, females experience more severe disease than males. While obese patients had higher prevalence of NAFLD/NASH, nonobese individuals (body mass index [BMI] <25 kg/m²) consistently comprised 20% to >35% of NAFLD and NASH patients. The evidence shows that, despite obesity being linked with worse disease stages, “lean‐NASH” also plays an important role in NASH epidemiology. Besides obesity, diabetes and metabolic syndrome appeared to be reliably associated with disease severity. The prevalence of advanced fibrosis or cirrhotic disease was the highest in patients with NASH‐HCC (44–80% with stage F3/F4 disease), while 21–50% of patients with NASH had F3/F4 disease. NAFLD/NASH is common in the Japanese population, and the prevalence of these conditions has tripled in the last two decades. Furthermore, these NAFLD/NASH patients have a high comorbidity burden. Early and efficient identification of safe and effective treatments for NAFLD/NASH patients is urgently needed.

Characteristics of non-alcoholic steatohepatitis among lean patients in Japan: Not uncommon and not always benign

BACKGROUND AND AIM

To elucidate features of nonobese non-alcoholic fatty liver disease (NAFLD), we assessed Japanese patients with NAFLD stratified by body mass index (BMI) and by sex.

METHODS

Biopsy-proven 762 NAFLD patients (404 men) were classified into three groups by the Japanese criteria: nonobese group (BMI < 25 kg/m² ), obese group (25 to 30), and severely obese group (≥ 30). Clinicopathological features and single nucleotide polymorphism of patatin-like phospholipase 3 (PNPLA3) rs738409 were investigated, and body composition analysis was performed by bioelectrical impedance analysis and computed tomography.

RESULTS

Over 25% of men and almost 40% of women were nonobese, but most of them had visceral fat obesity and/or insulin resistance. The median age (years) of the nonobese, obese, and severely obese men was 49.9, 46.8, and 40.5 (P < 0.01), respectively, while those of women was 60.2, 59.6, and 48.5 (P < 0.01), respectively. The prevalence of metabolic comorbidities and PNPLA3 risk alleles did not differ among these groups in both sexes. Also, the prevalence of non-alcoholic steatohepatitis was not significantly different in both sexes, although nonobese patients had a higher prevalence of mild steatosis. Advanced fibrosis showed a marked difference between men and women. Advanced fibrosis was significantly more frequent among severely obese men (nonobese: 31.0%, obese: 41.6%, severely obese: 60.9%; P < 0.01), but it was lower among severely obese women (51.4%, 62.9%, 33.7%; P < 0.01). Skeletal muscle mass was significantly lower in nonobese patients.

CONCLUSIONS

Non-alcoholic fatty liver disease was not milder in nonobese patients. Histological steatosis was associated with BMI, but advanced fibrosis was not and showed a significant sex difference.