Americans Are Getting Fatter, and So Are Their Livers

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Americans Are Getting Fatter, and So Are Their Livers

April 21, 2011 (Berlin, Germany) — As the belly goes, so goes the liver. The epidemic of obesity in the United States is adding to the prevalence of nonalcoholic fatty liver disease (NAFLD), according to study results based on successive National Health and Nutrition Examination Survey (NHANES) cycles and reported here at the European Association for the Study of the Liver (EASL) 46th Annual Meeting.

Zobair Younossi, MD, MPH, and colleagues showed a steadily increasing prevalence of NAFLD during each of 3 NHANES periods — 1988 to 1994, 1999 to 2004, and 2005 to 2008 — paralleling the rise in obesity. The 3 survey cycles included a total of 39,500 adults with complete clinico-demographic data.

Over time, NAFLD prevalence increased from 5.51% ± 0.31% in the first period to 9.84% ± 0.33% in the second, and to 11.01% ± 0.51% by 2005 to 2008 (P < .001).

Dr. Younossi, vice president for research for Inova Health System and executive director of the Center for Liver Diseases at Inova Fairfax Hospital in Falls Church, Virginia, said the true prevalence of NAFLD may be even higher than what he and his colleagues found, as some people with NAFLD may have normal serum liver enzyme levels that could be missed according to criteria for the condition. "Therefore, I suspect the prevalence will be closer to 20% to 25%," he said. EASL has a similar estimate of 20% to 30% prevalence in Western countries.

Although the prevalence rate of chronic liver disease (CLD) leveled off at about 14.8% by 2005 to 2008, according to analysis of the NHANES data, NAFLD made up an increasing proportion of CLD: 46.8% ± 1.9% in 1998 to 1994, 62.84% ± 1.52% in 1994 to 2004, and 75.1% ± 1.6% in 2005 to 2008 (P < .001).

The researchers found that several risk factors for NAFLD increased during the same time periods, including obesity, visceral obesity, type 2 diabetes, insulin resistance, and hypertension. By multivariate analysis, obesity (body mass index > 30 kg/m2), and type 2 diabetes were independent predictors of NAFLD in all 3 NHANES cycles. In the 2005 to 2008 cycle, the prevalence of obesity had increased to 33.22% ± 1.08%, and the prevalence of type 2 diabetes was up to 9.11% ± 0.47% (both P < .001 compared with earlier periods).

The researchers predicted that if the current rates of increase in obesity and diabetes continue for another 2 decades, the prevalence of NAFLD in the United States would be expected to increase by 50% and to substantially contribute to the amount of CLD.

Mark Thursz, MD, EASL vice secretary and professor of hepatology at Imperial College, London, United Kingdom, who was not involved in the study, commented that NAFLD is becoming a top concern for clinicians in light of the obesity epidemic. Because it can progress to advanced liver disease, including fibrosis, cirrhosis, liver failure, cancer, and eventually death, it significantly contributes to the burden of liver morbidity and mortality.

"If the obesity epidemic is anything to go by, the US NAFLD epidemic may have a ripple effect worldwide," Dr. Thursz said. Health systems need to promote awareness of obesity and its dangers and emphasize the importance of diet and exercise, he advised. NAFLD may be reversible with weight loss and lifestyle interventions.

Dr. Younossi said the best data in this regard come from very obese patients undergoing bariatric surgery. Even with very severe NAFLD at baseline, "some of these patients...with adequate weight loss and resolution of [insulin resistance/diabetes mellitus], their liver disease improves or completely resolves," he said.

Dr. Younossi and Dr. Thursz have disclosed no relevant financial relationships.

European Association for the Study of the Liver (EASL) 46th Annual Meeting: Oral Session. Presented March 31, 2011.

http://www.medscape.com/viewarticle/741246