Mortality from ischemic heart disease and diabetes mellitus (type 2) in four U.S. wheat-producing states: a hypothesis-generating study

Abstract

In this ecologic study I examined ischemic heart disease (IHD) and diabetes mortality in rural agricultural counties of Minnesota, Montana, North Dakota, and South Dakota, in association with environmental exposure to chlorophenoxy herbicides, using wheat acreage as a surrogate exposure. I collected data on agricultural land use and 1979-1998 mortality from the U.S. Department of Agriculture and the Centers for Disease Control and Prevention websites, respectively. Counties were grouped based on percentage of land area dedicated to wheat farming. Poisson relative risks (RR) and 95% confidence intervals (CIs), comparing high- and medium- with low-wheat counties, were obtained for IHD, the subcategories acute myocardial infarction (AMI) and coronary atherosclerosis (CAS), and diabetes, adjusting for sex, age, mortality cohort, and poverty index. Mortality from IHD was modestly increased (RR = 1.08; 95% CI, 1.04-1.12). Analyses of its two major forms were more revealing. Compared with low-wheat counties, mortality in high-wheat counties from AMI increased (RR = 1.20; 95% CI, 1.14-1.26), and mortality from CAS decreased (RR = 0.89; 95% CI, 0.83-0.96). Mortality from AMI was more pronounced for those < 65 years of age (RR = 1.31; 95% CI 1.22-1.39). Mortality from type 2 diabetes increased (RR = 1.16; 95% CI, 1.08-1.24). These results suggest that the underlying cause of mortality from AMI and type 2 diabetes increased and the underlying cause of mortality from CAS decreased in counties where a large proportion of the land area is dedicated to spring and durum wheat farming. Firm conclusions on causal inference cannot be reached until more definitive studies have been conducted.

Figure 1

IHD (ICD-9 410–414.9): Age-standardized mortality rates/100,000 (underlying cause) for grouped counties based on tertiles of percentage of a county’s land area dedicated to wheat. Comparison of high-wheat (H) and medium-wheat counties (M) with low-wheat counties (L), by age group, sex, and mortality cohort. (A) Age 25– ≥ 85 years; (B) Age 25–64 years; (C) Age 65– ≥ 85 years.

Figure 2

AMI (ICD-9 410): Age-standardized mortality rates/100,000 (underlying cause) for grouped counties based on tertiles of percentage of a county’s land area dedicated to wheat. Comparison of high-wheat (H) and medium-wheat counties (M) with low-wheat counties (L), by age group, sex, and mortality cohort. (A) Age 25– ≥ 85 years; (B) Age 25–64 years; (C) Age 65– ≥ 85 years.

Figure 3

CAS (ICD-9 414.0): Age-standardized mortality rates/100,000 (underlying cause) for grouped counties based on tertiles of percentage of a county’s land area dedicated to wheat. Comparison of high-wheat (H) and medium-wheat counties (M) with low-wheat counties (L), by age group, sex, and mortality cohort. (A) Age 25– ≥ 85 years; (B) Age 25–64 years; (C) Age 65– ≥ 85 years.

Figure 4

Diabetes mellitus (ICD-9 250.0–250.9): Age-standardized mortality rates/100,000 (underlying cause) for grouped counties based on median of percentage of a county’s land area dedicated to wheat. Comparison of high-wheat counties (H) with low-wheat counties (L), by age group, sex, and mortality cohort. (A) Age 45– ≥ 85 years; (B) Age 45–64 years; (C) Age 65– ≥ 85 years.