Background: Fatty liver not caused by excess alcohol intake or medicinal, viral or autoimmune causes is the most common cause of chronic liver disease in Western countries. Fatty liver is defined as a condition in which more than 5-10% of hepatocytes exhibit steatosis. Fatty liver is often accompanied by metabolic. disturbances. It is a reversible condition, but it may progress into the more severe inflammatory condition, steatohepatitis, and in some cases result in permanent damage, liver cirrhosis. This is the rationale for assessing the determinants and risk factors of fatty liver. 

Aims: The aims of this thesis were: to study risk factor levels for fatty liver in the Finnish adult population; investigate childhood risk factors and genetic predictors for adult fatty liver; and study the prediction between circulating metabolites and a fatty liver. 

Participants and methods: This thesis uses data from the Cardiovascular Risk in Young Finns Study, an ongoing population-based multicenter follow-up study in Finland initiated in 1980. The 31-year follow-up was conducted in 2011 with a total of 2,063 participants; of these, a liver ultrasound to assess fatty liver was performed on 2,042 (mean age 41.4 years and 55% women). 

Results: Prevalence of fatty liver was 19% among study participants. Adulthood risk factors of fatty liver were increased waist circumference and BMI, high alanine aminotransferase, male sex, increased apolipoprotein B concentration, elevated systolic blood pressure, high alcohol intake, high serum fasting insulin concentration and low physical activity index. Childhood risk factors for adult fatty liver included low birth weight, high BMI, and high serum insulin concentration. In addition, genetic variants and certain circulating small molecular weight metabolites, including lipids, fatty acids and amino acids, measured in adulthood were associated with fatty liver. 

Conclusions: Fatty liver relates to components of metabolic syndrome both in childhood and adulthood. By utilizing knowledge of genetic variants and circulating metabolites, individuals at a high risk for fatty liver could be better recognized.