"Physicians have considered fatty liver disease a really worrisome risk factor for cardiovascular disease," study leader Mariana Lazo, a postdoctoral fellow at the Johns Hopkins University School of Medicine, said in a statement.
"Our data analysis shows this doesn't appear to be the case. We were surprised, to say the least, because we expected to learn by how much non-alcoholic fatty liver disease increased the risk of death, and instead found the answer was not at all."
The study involved data from 11,371 Americans from 1994 to 1998 who were followed for up to 18 years as part of the Third National Health and Nutrition Examination Survey.
The researchers checked liver enzyme levels and ultrasound tests and ultimately looked at death rates associated with non-alcoholic fatty liver disease. The participants ranged in age from 20 to 74 during the data collection years.
Because the ultrasounds were originally taken to assess gallbladder health, Lazo and colleagues looked at each recording to determine the presence of fat in each person's liver. People whose livers are 5 percent fat or more are considered to have non-alcoholic fatty liver disease, Lazo said.
The study, published in the British Medical Journal, found no increase in mortality among those with non-alcoholic fatty liver disease, which was identified in about 20 percent of the NHANES participants.