Pesticide exposure and self-reported incident depression among wives in the Agricultural Health Study

Abstract

Background: Depression in women is a public health problem. Studies have reported positive associations between pesticides and depression, but few studies were prospective or presented results for women separately.

Objectives: We evaluated associations between pesticide exposure and incident depression among farmers' wives in the Agricultural Health Study, a prospective cohort study in Iowa and North Carolina.

Methods: We used data on 16,893 wives who did not report physician-diagnosed depression at enrollment (1993-1997) and who completed a follow-up telephone interview (2005-2010). Among these wives, 1054 reported physician diagnoses of depression at follow-up. We collected information on potential confounders and on ever use of any pesticide, 11 functional and chemical classes of pesticides, and 50 specific pesticides by wives and their husbands via self-administered questionnaires at enrollment. We used inverse probability weighting to adjust for potential confounders and to account for possible selection bias induced by the death or loss of 10,639 wives during follow-up. We used log-binomial regression models to estimate risk ratios and 95% confidence intervals.

Results: After weighting for age at enrollment, state of residence, education level, diabetes diagnosis, and drop out, wives' incident depression was positively associated with diagnosed pesticide poisoning, but was not associated with ever using any pesticide. Use of individual pesticides or functional or chemical classes of pesticides was generally not associated with wives' depression. Among wives who never used pesticides, husbands' ever use of individual pesticides or functional or chemical classes of pesticides was generally not associated with wives' incident depression.

Conclusions: Our study adds further evidence that high level pesticide exposure, such as pesticide poisoning, is associated with increased risk of depression and sets a lower bound on the level of exposure related to depression, thereby providing reassurance that the moderate levels of pesticide exposure experienced by farmers' wives likely do not increase risk.

Keywords: (2,4,5-trichlorophenoxy)acetic acid; (RS)2-(2,4,5-trichlorophenoxy)propanonic acid; 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane; 2,4,5-T; 2,4,5-TP; 2,4-D; 2-(2,4-dichlorophenoxy)acetic acid; CI; Confidence interval; DDT; Depression; EPTC; Female; IQR; Incidence; Interquartile range; NIEHS; National Institute of Environmental Health Sciences; Pesticides; RR; Risk ratio; S-ethyl dipropyl(thiocarbamate); Spouses.

Figure 1

Flow diagram depicting the study population for an analysis of pesticide use and self-reported, incident depression in wives from Iowa and North Carolina enrolled in the Agricultural Health Study. Boxes or lines marked with solid lines represent individuals who remained in the study after each step shown, whereas boxes or lines marked with small dashes represent individuals who were excluded after each step shown (see “2.1. Study population and case definition” for more details). Boxes or lines marked with large dashes represent individuals who, although not directly included in the analysis, were incorporated into the analysis via inverse probability weighting (see “2.3. Statistical analyses” for more details).