The questionnaire response rate was 69%. The 114,562 respondents were divided into groups based on self-perceived exposure (no, low, moderate, high) and qualitative exposure level, derived from service history (battalion/company, division/brigade). After adjusting for BMI, smoking, alcohol use, physical activity, use of nonoccupational herbicides, education, income, and military rank, Yi and colleagues found a statistically significant association of hypertension and self-reported perceived Agent Orange exposure (P < .001) and a statistically significant association of hypertension and exposure in the division/brigade group with the highest exposure level (P < .001).11 The highest ORs were found for high- vs low-exposure and moderate- vs low-exposure subsets in self-reported perceived Agent Orange levels: 1.60 (95% CI, 1.56-1.65) and 1.70 (95% CI, 1.64-1.77), respectively. However, adjusted ORs in proximity-based exposure for all groups were > 1.03.
Inuits in Canada and Greenland
To study total PCBs, non-dioxin-like PCBs, OC pesticides, and their metabolites in plasma, public health researchers Valera and colleagues focused on the Inuit town of Nunavik (in Canada), where there is contamination from foods like fish, a mainstay of the Inuit diet.5 A health survey was sent to 400 households randomly selected from 1,378 households in 14 villages. Data were collected between September and December 1992. In total, 518 people between ages 18 and 74 years agreed to undergo a physical examination, and 492 agreed to have blood drawn. Laboratories measured serum PCB congeners and 13 chlorinated pesticides or their metabolites. Blood pressure (BP) was measured 3 times, and the last 2 measurements averaged. Hypertension was defined as SBP ≥ 140 mm Hg and/or DBP ≥ 90 mm Hg.
Of the 518 participants, 315 (134 men, 181 women) had complete BP, serum POP levels, and confounding variables recorded, and these were subsequently analyzed. Mean age was 32.7 years. Polychlorinated biphenyls congeners 105 and 118 were higher in women than in men; no other congeners were quantitatively different. Associations between POP levels and hypertension were analyzed with multiple logistic regression modeling, with adjustments for age, sex, fasting blood glucose, waist circumference, smoking, alcohol use, and physical activity, as well as the common contaminants lead, mercury, and omega-3 polyunsaturated fatty acids (n-3 PUFA).The researchers adjusted for n-3 PUFA because of the posited BP-lowering effects. Inuits consume large amounts of the polyunsaturated fatty acids DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid).5
Using congeners found in at least 70% of the total samples, the study authors found a statistically significant association between certain PCBs, both dioxin-like (DL-PCBs) and non-dioxin-like (NDL-PCBs), and increased risk of hypertension. Congeners 101, 105 (DL-PCB), 138, and 187, as well as p,p'-DDE, were also significantly associated with a higher risk of hypertension. Congener 99 was associated with increased SBP, and congener 118 (DL-PCB) was associated with increased SBP and DBP. Some congeners, such as the OC pesticides, p,p'-DDT, β-hexachlorocyclohexane, and oxychlordane, were inversely associated with hypertension.
In 2012, Valera and colleagues conducted a similar study of Greenland Inuits who also consume marine mammals and fish and present with high POP levels.6 Despite correcting for n-3 PUFA, they found no significant association involving DL-PCBs, NDL-PCBs, or OC pesticides.
Japanese Background Exposures
Nakamoto and colleagues conducted a cross-sectional study of 2,266 Japanese women and men who had been exposed to background (vs occupational or wartime) levels of dioxins, including PCDDs, PCDFs, and DL-PCBs.12 The dioxins likely originated from combustion of chlorinated materials and older manufactured electronics components. The study participants had lived in urban areas or in farming or fishing villages for at least 10 consecutive years and had no concomitant occupational exposure to dioxins. Mean (SD) age was 43.5 (13.6) years for the men and 45.3 (14.0) years for the women. Participants volunteered their disease histories, which included physician-diagnosed hypertension (SBP ≥ 140 mm Hg or DBP ≥ 90 mm Hg). Logistic regression analyses were adjusted for BMI, sex, age, regional residential area, smoking, alcohol use, and survey year. In fishing regions, PCDDs, PCDFs, and DL-PCBs were significantly higher than in the other regions. Of the 2,266 participants, 647 reported physician-diagnosed hypertension. Dividing the toxic equivalents of serum COI levels into quartiles of concentration, Nakamoto and colleagues found a statistically significant association of hypertension and increased toxic equivalent levels of PCDDs, PCDFs, DL-PCBs, and total dioxins.
Italian Male Steelworkers
In a 2016 retrospective cohort study, Cappelletti and colleagues assessed the health burden of workers at a steel recycling plant in Trento, Italy. The plant, which had been using an electric arc furnace without a coke oven, had been exposing workers to dust containing PCBs, PCDDs, PCDFs, and other metals.13 Each hour, roughly 2 to 5 kg of dust was being released inside the plant (diffuse emissions), and exposure extended to a 2-km radius around the plant. A cohort of 331 plant workers, identified and assessed through company records, had been exposed to diffuse emissions for at least 1 year between 1979 and 2009. This group was compared with a control group of 32 office workers from that company, as identified by company records. The authors found a risk ratio (RR) of 2.23 in cases of noncomplicated hypertension and an RR of 2.01 in cases of complicated hypertension, defined as hypertension with organ damage.