Diabetes in relation to serum levels of polychlorinated biphenyls and chlorinated pesticides in adult Native Americans

Diabetes is one of the most prevalent chronic diseases in developed countries, conferring a significant burden in terms of medical complications and health-care costs. Between 1980 and 2004, the number of Americans with diabetes increased from 5.8 million to 14.7 million. In 2004 alone, there were approximately 1.4 million new diagnoses of diabetes in American adults (18–79 years of age) [Centers for Disease Control and Prevention (CDC) 2005]. Incidence and prevalence of diabetes vary by age, ethnicity, and socioeconomic factors and are, in general, higher in Native Americans (CDC 2003a). Known risk factors for diabetes include obesity, genetic susceptibility, hyperinsulinemia (a marker for insulin resistance), sedentary lifestyle (Warram and Krolewski 2005), and cigarette smoking (Rimm et al. 1995; Will et al. 2001). Polychlorinated biphenyls (PCBs) were produced for use in various industries until the late 1970s when their production was banned. By then, large quantities of PCBs had been released into the environment. They are persistent substances both in the environment and in biota, and they bio-accumulate and biomagnify in the food chain. Once in the human body they persist for long periods, accumulating in adipose tissue and in the lipid component of serum. The Mohawk Nation at Akwesasne is a Native American population residing along the St. Lawrence River that separates New York State from Ontario and Quebec (Canada). Mohawks are traditionally a fish-eating community. There are three aluminum foundries just upriver from the reservation, namely the General Motors Central Foundry Division (a National Priority List site) and plants operated by Reynolds Metal and the Aluminum Company of America (ALCOA) (Hwang et al. 1993). PCBs (primarily Aroclor 1248) were used as hydraulic fluids at all three facilities. PCBs that leaked were washed into the St. Lawrence River and its tributaries. Via the air, soil, and water, PCBs contaminated the environment and local flora and fauna, and entered the food chain. Although they are only modestly elevated, PCB levels in Mohawk breast milk (Hwang et al. 1996) and serum (Fitzgerald et al. 2004) have been correlated with rates of consumption of local fish, even though fish consumption has declined in recent years after issuance of advisories. Recent studies have reported an association between exposure to organochlorines and impaired blood-glucose regulation and diabetes. Several epidemiologic studies (Calvert et al. 1999; Pesatori et al. 1998; Vena et al. 1998) have shown that dioxin exposure is associated with elevated rates of diabetes and dysglycemia. U.S. Air Force veterans of Operation Ranch Hand, who applied Agent Orange in Vietnam, were exposed to dioxin. Exposure was associated with an elevated incidence of diabetes and was inversely associated with the length of time to diabetes onset (Henriksen et al. 1997). Cranmer et al. (2000) reported that dioxin exposure resulted in hyperinsulinemia and insulin resistance, and Fierens et al. (2003) reported significant odds ratios (ORs) of 5.1, 13.3, and 7.6 for risk of diabetes in relation to top decile concentrations of dioxins, coplanar PCBs, and 12 PCB markers. Longnecker et al. (2001) reported that pregnant women with diabetes had higher PCB levels than did nondiabetic pregnant women. Radikova et al. (2004) reported that PCB concentrations in a Slovak population were associated with elevated levels of blood glucose. Vasiliu et al. (2006) found a linear association between PCB serum levels and diabetes incidence in a large cohort in Michigan, and Lee et al. (2006) found a strong dose–response relationship between serum concentrations of six persistent organic pollutants [PCB-153, two dioxin congeners, oxychlordane, dichlorodiphenyldichloroethylene (DDE), and trans-nonachlor] and diabetes. Everett et al. (2006) reported an association between serum levels of both PCB-126 (a dioxin-like PCB) and p,p′-DDT (dichlorodiphenyltrichloroethane). DDE, the major metabolite of DDT, has previously been reported to be associated with diabetes (Glynn et al. 2003; Rylander et al. 2005), and hexachlorobenzene (HCB) was also linked to diabetes in cross-sectional studies (Glynn et al. 2003). Lee et al. (2007) have expanded their study to analyze the data from the sum of four dioxin-like PCB congeners and five nondioxin-like congeners, and report that the dioxin-like congeners showed the strongest relationship with diabetes. The present study was designed to investigate whether a relationship exists between diabetes and serum levels of total PCBs, two single PCB congeners, and the chlorinated pesticides DDE, HCB, and mirex in adult Mohawks.