Increase in the prevalence of fatty liver in Japan over the past 12 years: analysis of clinical background

Background The aim of this investigation was to elucidate the time-course of changes in the prevalence of fatty liver, and to analyze its clinical backgrounds over the previous 12-year period.Methods Thirty-nine thousand one hundred and fifty-one individuals who visited the Tokai University Hospital Health Checkup Center from 1989 to 2000 were examined for the presence of fatty liver, and their clinical backgrounds were analyzed.Results In 1989, the prevalence of fatty liver was 12.6%, and it rose gradually thereafter, reaching 30.3% in 1998, corresponding to a 2.4-fold increase over the prevalence rate in 1989. The average prevalence was about twice as high in males (26.0%) as in females (12.7%). The prevalence was uniformly high in males in all ages, while the prevalence in females tended to rise gradually with age. Body mass index (BMI) was found to be the variable most closely related to the onset of fatty liver. On the other hand, nonobese individuals with a BMI of less than 25kg/m² accounted for approximately half of all the patients with fatty liver, and this proportion remained almost unchanged during the 12-year survey period. It was therefore difficult to simply attribute the increase in the prevalence of fatty liver to the increased prevalence of obesity. In the 35519 repeat examinees (repeaters), it was found that 5088 individuals (14.3%) developed fatty liver, and fatty liver resolved in 1248 individuals (3.5%). As fatty liver developed, the BMI increased by 1.0 ± 1.3kg/m². As fatty liver disappeared, the BMI decreased by 1.0 ± 1.5kg/m².Conclusions These results suggest that the absolute value of the BMI, as well as the relative changes in the BMI in each individual, may be related to the onset of fatty liver.