Lead, mercury, dieldrin, and heptachlor may explain a significant quantity of the excess liver disease in U.S.
Researchers had previously found that a link between high occupational exposures to chemicals and liver disease, but it had remained unknown whether chronic, low-level exposure to pollutants was associated with liver abnormalities in the general population. To address that question they used data from the National Health & Nutrition Examination Survey (NHANES) for 2003-2004. The researchers identified adults with detectable levels of 196 different pollutants in their blood or urine; however, only the 111 toxicants present in 60% or more of the participants were included in the analysis.
Among the NHANES population, the researchers noted that more than one-third of U.S. adults (37.6%) had elevated alanine aminotransferase (known as the ALT) levels [see http://en.wikipedia.org/wiki/Alanine_aminotransferase], even after those with risk factors such as Hepatitis B or C infection, a history of alcohol abuse, or iron overload were excluded. (Elevated ALT levels were defined as greater than 30 U/L for men and 19 U/L for women). Cross-sectional analyses found that at least some of the elevated ALT levels may be attributable to exposure to environmental pollutants. The researchers noted that an estimated 70 million U.S. adults have liver disease not explained by traditional risk factors, which is usually attributed in large measure to nonalcoholic fatty liver disease [http://en.wikipedia.org/wiki/Non-alcoholic_fatty_liver_disease].
At the class level, increasing levels of heavy metals (P=0.015) and pesticides (P<0.001) were both associated with higher odds of having elevated ALT levels after adjusting for age, sex, race, poverty, insulin resistance, and body mass index. Participants who had the highest levels of mercury had double the risk of an elevated ALT, the surrogate for liver disease (OR 2.2, P<0.001), and those who had the highest levels of lead had triple the risk (OR 3.3, P=0.026). Higher levels of two organochlorine pesticides banned in the U.S. for almost all purposes since the 1970s and 1980s, dieldrin (P=0.027) and heptachlor epoxide (P=0.009), were also significantly associated with an increased risk of liver disease. The researchers believe the primary route of exposure is through the food supply.
The researchers noted that a cross-sectional analysis cannot prove causality. Playing devil’s advocate, one could argue, they noted, that patients with liver disease are less capable of metabolizing these pollutants, and that explains the higher levels. However, since animal studies have shown that these pesticides and other pollutants cause liver disease, they may very well be the actual cause.