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Rise in adolescent NAFLD outpacing obesity.

Obese children have gotten fatter around the middle over time, a development that may account in part for an observed increase in suspected nonalcoholic fatty liver disease among adolescents.

Nonalcoholic fatty liver disease (NAFLD) in adolescents has nearly tripled from 1998 to 2008, said Dr. Miriam Vos, who presented the results of an observational study. In a review of nationally representative data from the National Health and Nutrition Examination Survey (NHANES), the tripling of NAFLD cases out-paced a near doubling of adolescent obesity during the same period.

Thus, "our findings suggest that obesity alone does not explain the growing prevalence of the liver disease," she said.

The most common cause of chronic pediatric liver disease, NAFLD has been linked with hypertension, type 2 diabetes, metabolic abnormalities, liver damage, and cancer. Anecdotal data have suggested a risk in NAFLD that was linked to obesity in children, but "this Finding has not been confirmed in previous studies," said Dr. Vos of Children's Healthcare of Atlanta. "We wanted to know whether the rates seem high because clinicians are looking more closely [for NAFLD] or because there really are more cases."

The researchers used NHANES data sets from 1988 to 2008, which account for 10,359 12- to 18-year-olds after those with incomplete information or known liver disease were excluded.

More conservative cutoff parameters for suspected NAFLD were implemented during the period of the study, so the researchers conducted their analyses using both cutoffs to allow for comparisons with earlier studies, Dr. Vos noted. "Based on the earlier cut-off, [NAFLD] was suspected in adolescents with a BMI [body mass index] in the 85th percentile or higher, and elevated [ALT] levels (defined as greater than 30)," she said. The newly recommended ALT cutoffs are sex-specific; NAFLD is suspected in adolescents in the same BMI range, but at ALT levels greater than 25.8 for boys and 22.1 for girls (Gastroenterology 2010;138:1357-64).


When the sex-specific cutoffs were used, NAFLD rates "increased among all adolescents, from 3.6% to 9.9%," Dr. Vos said. Age, sex, race, and percentage of overweight adolescents did not differ from 1988 to 2008; however, the percentage of overweight adolescents who were obese increased significantly (from 11.2% to 20.6%).

Among overweight adolescents, the prevalence of elevated ALT levels was 13.2% in 2007-2008, which did not represent a significant linear increase over time. Among obese adolescents, however, elevated ALT levels rose from 16.7% to 36.9% from 1988 to 2008. Similar increases were observed in this group when the previous ALT cutoff of 30 was used.

Dr. Vos cited a study limitation: "It's tricky to identify NAFLD using population data like this, so we set our definition to look at overweight children who also have elevated serum ALT. By choosing to look only at the overweight children, we might have missed some cases."

Dr. Vos has received funding from the National Institute of Diabetes and Digestive and Kidney Diseases, and the Children's Digestive Health and Nutrition Foundation. She receives royalties for "The No-Diet Obesity Solution for Kids" (Bethesda, Md.: AGA Institute Press, 2009).



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Title Annotation:nonalcoholic fatty liver disease; OBESITY
Author:Mahoney, Diana
Publication:Family Practice News
Date:Jun 1, 2012
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