Exposure to livestock may have protective effect

A new study on the wives of pesticide applicators showed that women who used (or were exposed via mixing activities on the farm) the pesticides glyphosate and maneb/mancozeb had a higher risk of developing rheumatoid arthritis than non-users of pesticides.

The elevated risk for glyphosate users was 1.4 times that of non-users of pesticides.

The confidence interval for glyphosate (expressed as “OR=1.4; 95%CI 1.0, 2.1”) means that there is 95% probability that exposure to that pesticide actually does raise the risk of rheumatoid arthritis by between 1 time (no effect) and 2.1 times – as opposed to the possibility that the effect is due to chance.

Potential link with cancer

Interestingly, some autoimmune and chronic inflammatory disorders such as rheumatoid arthritis are associated in other studies with increased risk of certain types of cancer, including non-Hodgkin lymphoma. Non-Hodgkin lymphoma was correlated with glyphosate exposure in the assessment by the World Health Organisation’s cancer agency IARC. This raises the possibility that rheumatoid arthritis and Non-Hodgkin lymphoma share a common causative factor.

Exposure to livestock may have protective effect

The new study also found that lifelong exposure to livestock seems to have a protective effect against developing rheumatoid arthritis. The authors suggest a possible reason: “Early life exposures to infections, the microbiome, and microbial products, such as endotoxin, are known to play an important role in programming immune system responses in later life”.

The study was supported by finding from the US National Institutes of Health, the National Institute of Environmental Health Sciences, and the National Cancer Institute.

The study abstract is below and the full paper is open access.

Rheumatoid Arthritis in Agricultural Health Study Spouses: Associations with Pesticides and Other Farm Exposures
Christine G. Parks, Jane A. Hoppin, Anneclaire J. DeRoos, Karen H. Costenbader, Michael C. Alavanja, and Dale P. Sandler
Environ Health Perspect; DOI:10.1289/EHP129 (open access)

Background: Farming has been associated with rheumatoid arthritis (RA), but the role of pesticides is not known.

Objectives: We examined associations between RA and pesticides or other agricultural exposures among female spouses of licensed pesticide applicators in the Agricultural Health Study.

Methods: Women were enrolled 1993-1997 and followed through 2010. Cases (N=275 total, 132 incident), confirmed by a physician or by self-reported use of disease modifying anti-rheumatic drugs), were compared with non-cases (N=24,018). Odds ratios (OR) and 95% Confidence Intervals (CI) were estimated using logistic regression models adjusted for age, state and smoking pack-years.

Results: Overall, women with RA were somewhat more likely to have reported lifetime use of any specific pesticide versus no pesticides (OR=1.4; 95%CI 1.0, 1.6). Of 15 pesticides examined, maneb/mancozeb (OR=3.3; 95%CI 1.5, 7.1) and glyphosate (OR=1.4; 95%CI 1.0, 2.1) were associated with incident RA compared with no pesticide use. An elevated, but non-statistically significant association with incident RA was seen for DDT (OR=1.9; 95%CI 0.97, 3.6). Incident RA was also associated with the application of chemical fertilizers (OR=1.7; 95%CI 1.1, 2.7) and cleaning with solvents (OR=1.6; 95%CI 1.1, 2.4), but inversely associated with lifetime livestock exposure as a child and adult (OR=0.48; 95%CI 0.24, 0.97) compared with no livestock exposure.

Conclusions: Our results suggest that specific agricultural pesticides, solvents and chemical fertilizers may increase risk of RA in women, while exposures involving animal contact may be protective.