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By: MARY ANN MOON, Internal Medicine News Digital Network

Nonalcoholic fatty liver disease may soon become the most important cause of chronic liver disease in the United States, "with a substantial clinical and economic impact," Dr. Zobair M. Younossi, AGAF, and his colleagues reported in the June issue of Clinical Gastroenterology and Hepatology.

In what they described as the first population-based study to assess changes in the prevalence of chronic liver diseases over the past 20 years, the authors found that the prevalence is steadily rising in only one major category: nonalcoholic fatty liver disease (NAFLD). In contrast, rates of chronic liver disease related to hepatitis B virus, hepatitis C virus, and alcohol use have remained stable (Clin. Gastroenterol. Hepatol. 2011 June [doi: 10.1016/j.cgh.2011.03.020]).

The rise in NAFLD correlates with the well-known increases in obesity and type 2 diabetes, and the study findings suggest that liver disease "will remain among the major causes of mortality and morbidity in the U.S. and will be responsible for substantial medical resource utilization."

"This issue becomes especially important as we face a potential decline in the availability of resources dedicated to the care of patients with chronic diseases, as well as the expected shortage of individuals trained in hepatology who are available to care for these patients," said Dr. Younossi, executive director of the Center for Liver Diseases at Inova Fairfax (Va.) Hospital, and his associates.

The investigators used data from the National Health and Nutrition Examination Survey (NHANES), the CDC’s assessments of health and nutrition in nationally representative samples of the adult population, to track trends in chronic liver disease during three periods: 1988-1994 (15,855 subjects), 1999-2004 (13,970 subjects), and 2005-2008 (9,670 subjects).

The prevalence of the four types of chronic liver disease combined increased during this 20-year interval, from 12% to 15%. However, that was driven entirely by the increasing prevalence of NAFLD-related liver disease alone, which rose from 5.5% in 1988-1994, to 9.8% in 1999-2004, to 11.0% in 2005-2008.

In contrast, the prevalence of chronic liver disease related to hepatitis B remained stable (0.4%, 0.3%, and 0.3%, respectively), as did that related to hepatitis C (2%, 2%, and 2%, respectively). The prevalence of alcohol-related chronic liver disease also remained stable over the 3 time periods, at 1.4%, 2%, and 2%, respectively.

In a further analysis of the data, the researchers found that the proportion of chronic liver disease attributable to NAFLD also rose significantly during these three time periods. NAFLD accounted for 47% of chronic liver disease in 1988-1994, which increased to 63% in 1999-2004 and to 75% in 2005-2008.

To assess the underlying causes of this increase in NAFLD, the investigators studied changes in the rates of metabolic syndrome components, all of which are known to be risk factors for NAFLD.

Significant increases during this same time span were found for prevalence of obesity, visceral obesity, type 2 diabetes, insulin resistance, and hypertension. Hypercholesterolemia was the only component of the metabolic syndrome that did not rise significantly.

"We postulate that by treating components of the metabolic syndrome in patients with chronic liver disease, we may be able to ameliorate the anticipated wave of liver disease complications in the U.S.," the investigators said.

To do so, "we must expand patients’ access to care and the availability of insurance coverage, encourage more targeted treatment strategies, and increase the training of experts and health care extenders capable of delivering care to these patients," they added.

This study included only adults, but "given the reports from other databases and tertiary care centers regarding children with liver disease, we suspect that our findings are applicable to children and adolescents in the U.S."

"The increasing prevalence of obesity and NAFLD among U.S. children and adolescents makes the future projections even direr," the authors wrote.

"As this young population ages, they are expected to become more obese and more likely to develop type 2 diabetes, both of which can lead to even higher rates of NAFLD. This cohort will certainly contribute to the future burden of chronic liver disease ... which could potentially become overwhelming," they said.

Dr. Younossi and his associates reported that they have no conflicts of interest. The study was conducted with internal funds only.