CHICAGO (Reuters Health) – An analysis of data from a sample of participants in the National Health and Nutrition Examination Survey (NHANES) 2003-2004 shows that the prevalence of abnormal alanine aminotransferase (ALT) levels in the US adult population is approximately 40%, even after excluding known risk factors for abnormal liver enzymes, such as alcohol abuse and viral hepatitis.
The findings were announced here Friday during Digestive Disease Week by Dr. Matthew Cave of the University of Louisville, Kentucky.
Dr. Cave and colleagues evaluated approximately 4,500 adults in NHANES, analyzing blood and urine specimens for levels of 196 toxicants. They found 111 chemical pollutants in more than 60% of NHANES subjects. Abnormal ALT levels were defined as greater than 30 U/l for men and greater than 19 U/l for women.
“We used a relatively low cutoff defining the normal range of ALT,” Dr. Cave commented during the announcement of his group’s findings. “We estimate that by current population measures that approximately 70 million U.S. adults have elevated ALT not explained by traditional risk factors such as alcohol and hepatitis C. And while some of these cases, and perhaps the majority, may be explained by obesity and the metabolic syndrome, we believe that some of them may be due to environmental pollution.”
In addition, “than one in three U.S. adults had liver disease, even after excluding those with traditional risk factors,” Dr. Cave told reporters at a briefing. “Some of these cases may be attributable to environmental pollution.”
“We found several chemicals associated with a dose-dependent increase risk for abnormal liver enzymes.” These “included lead, mercury, thallium, organochloride pesticides and dibenzofuran,” Dr. Cave added. “These associations were significant even after we adjusted for potentially confounding variables such as obesity, diabetes, race, sex and poverty.”
He speculates that “these results indicate that there may be a previously unexpected role for environmental pollution in the rising incidence of liver disease in the U.S. population.”
“The really surprising thing was that essentially 100% of these people had detectable levels of PCPs in their sera, despite the fact that these chemicals were banned more than 20 years ago. It leaves us to wonder if liver disease is a legacy from our fathers’ time?”
“It also makes us wonder, ‘what about people, like farmers, who also drink, and take other medications that involve liver enzyme pathways or have other stressors on their livers? What is the effect of (these pollutants) in the face of multiple causes of liver disease, especially given the fact that close to 40% of the population has elevated ALT levels with no significant risk factors’?”
“A major limitation of the study is that this is just an association that we determined and that doesn’t prove causality,” Dr. Cave cautioned. “However, multiple previous animal studies have demonstrated the presence of liver disease in mice or rats treated with many of these chemicals…these animal data suggest, but again, do not prove, that pollutant exposure does play a causal role in liver disease in the U.S. population.”