Occupational Exposures to Vapors and Gases, Liver Attenuation and Insulin Resistance

Thesis (Master's)--University of Washington, 2013Occupational exposures to vapors and gases, especially organic solvents, have been associated with liver toxicity. At high levels of exposure, solvents--characteristically chlorinated solvents--can cause overt hepatotoxicity, but at lower concentrations they have been associated with fatty liver disease. Accumulation of fat in the liver reflects metabolic changes, similar to those seen in insulin resistance and type 2 diabetes mellitus. Organic solvents are widely used in a variety of occupational settings. Few community-based studies have assessed occupational exposures and their associations with fatty liver disease or insulin resistance. This is the first large study to date to examine whether occupational exposure to solvents is associated with changes in liver fat or with insulin resistance. We evaluated relationships between occupational exposures, fatty liver disease, and insulin resistance in working participants aged 45-64 in the Multi-Ethnic Study of Atherosclerosis (MESA). Occupational classes were characterized as having a Vapor and Gas (VG) exposure that was low, medium, or high through the use of a job-exposure matrix, and we used this measure as a surrogate for occupational solvent exposure. Extent of fatty liver changes was measured by CT scan assessment of liver attenuation. Insulin resistance was assessed by the Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) via serum measurements of fasting insulin and glucose. We restricted our primary analyses to participants who drank less than 14 alcoholic beverages per week, and adjusted for age, sex, diabetes and adiposity. A small, but not statistically significant, decrease in hepatic attenuation (consistent with increased fat accumulation in the liver) was seen with increasing VG exposure. We did not observe a significant change in insulin resistance associated with an increase in VG exposure. As in other studies, decreased liver attenuation was strongly associated with obesity, diabetes and with alcohol consumptio