Effects of nonalcoholic fatty liver disease on the development of metabolic disorders

Nonalcoholic fatty liver disease (NAFLD) is considered to be the liver component of metabolic syndrome. However, the impact of NAFLD on metabolic syndrome is unclear. The aim of this study was to explore the influence of NAFLD on the development of metabolic disorders.

Patients with NAFLD and an age, sex, and occupation-matched control group were recruited from employees of Bao-Steel Group (Shanghai, China) who had received medical check-ups biennially between 1995 and 2002. Anthropometric and laboratory data, and incidence of metabolic disorders were assessed at baseline and at follow-up of at least 4 years. SPSS 11.5 was used for statistical analysis.

The study consisted of 358 patients (326 men and 32 women) and 788 matched controls (711 men and 77 women) with a similar mean age of 39.0 years and median follow-up of 6 years. At the end of follow-up, incidence of obesity (47.6% vs 19.5%), hypertension (69.6% vs 16.3%), hypertriglyceridemia (39.1% vs 16.3%), hypercholesterolemia (24.5% vs 17.3%), impaired fasting glucose (IFG) (25.1% vs 11.6%), diabetes mellitus (20.3% vs 5.2%) and multiple metabolic disorders (MMD) (56.3% vs 16.3%) were significantly higher in the fatty liver group than the control group. Interestingly, the mean alanine aminotransferase (ALT) level in patients with fatty liver significantly decreased at follow-up compared with baseline (28.56 +/- 18.86 vs 31.51 +/- 18.34 U/L, P < 0.05). To separate the effects of obesity from fatty liver, the subjects were re-classified according to the presence of obesity and fatty liver at baseline. The incidence of hypertension (61.1% vs 41.3%), hypertriglyceridemia (38.1% vs 15.0%), hypercholesterolemia (29.9% vs 16.6%), IFG (21.3% vs 10.0%) and diabetes (11.1% vs 4.3%) were significantly higher in the fatty liver group without obesity (n = 84) than in the group with without fatty liver or obesity (n = 614). In addition, the incidence of hypertension (72.9% vs 57.4%), hypertriglyceridemia (39.4% vs 22.7%) and diabetes (23.2% vs 8.4%) was higher in the group with fatty liver and obesity (n = 274) than in the group with obesity alone (n = 174).

The presence of NAFLD might predict the development of metabolic disorders due to insulin resistance, rather than obesity itself. ALT levels decreased over time in patients with fatty liver.