Table 2.

The association between exposure to herbicides and RA development.

Authors (Years)/Country	Study Design	Gender	Sample Size	Name of Chemicals	aOR (95% CI)	Confounding Variables
De Roos et al. (2005)/USA [17]	Case–control	Female	810	Herbicides Phenoxyacetic acids Triazines 2,4-D Alachlor Atrazine Cyanazine Glyphosate Imazethapyr Metolachlor	1.1 (0.8–1.6) 0.5 (0.3–0.9) 0.5 (0.2–1.3) 0.5 (0.3–0.9) 0.5 (0.1–1.6) 0.5 (0.2–1.6) 0.8 (0.2–3.4) 1.2 (0.8–1.8) 1.5 (0.5–4.1) 0.4 (0.1–1.7)	Birth date and state
Parks et al. (2016)/USA [20]	Cohort	Female	23,841	2,4-D Atrazine Glyphosate Imazethapyr Trifluralin Dicamba	0.75 (0.51–1.1) 0.65 (0.32–1.3) 1.2 (0.95–1.6) 1.1 (0.55–2.3) 0.57 (0.28–1.1) 0.68 (0.32–1.5)	Age, state, and pack-years smoking
Meyer et al. (2017)/USA [6]	Case–control	Male	26,354	2,4-D 2,4,5-T 2,4,5-TP Alachlor Atrazine Butylate Chlorimuron ethyl Cyanazine Dicamba EPTC Glyphosate Imazethapyr Metolachlor Metribuzin Paraquat Pendimethalin Trifluralin	1.16 (0.83–1.64) 1.11 (0.72–1.71) 1.00 (0.46–2.15) 1.26 (0.95–1.68) 1.29 (0.94–1.79) 1.04 (0.70–1.54) 1.45 (1.01–2.07) 0.96 (0.69–1.31) 0.90 (0.65–1.25) 0.62 (0.40–0.96) 0.90 (0.65–1.24) 1.32 (0.94–1.86) 0.90 (0.67–1.20) 1.08 (0.73–1.59) 0.92 (0.57–1.49) 0.98 (0.69–1.40) 1.23 (0.92–1.66)	Age, state of enrollment, pack-years smoking, and education level
Koureas et al. (2017)/Greece [21]	Cross- sectional	Male	170	Herbicides Paraquat	3.51 (0.45–27.20) 0.69 (0.09–5.03)	Age, smoker, alcohol consumption, and use of a tractor on a farm

aOR, adjusted odds ratio; 95% CI, 95% confidence interval; 2,4-D, 2,4-dichlorophenoxyacetic acid; 2,4,5-T, 2,4,5-trichlorophenoxyacetic acid; 2,4,5-TP, 2,4,5-trichlorophenoxy propionic acid; EPTC, S-ethyl-N, N-dipropylthiocarbamate.