Longitudinal Study of Thyroid Hormones between Conventional and Organic Farmers in Thailand

Abstract

Many pesticides are endocrine-disrupting chemicals that can interfere with hormone levels. This study aimed to assess the longitudinal impact of exposure to pesticides on thyroid hormone levels, including Thyroid Stimulating Hormone (TSH), Free Triiodothyronine (FT3), Free Thyroxine (FT4), Triiodothyronine (T3), and Thyroxine (T4). Both conventional (i.e., pesticide using) and organic farmers were interviewed using questionnaires, and blood samples were collected at 7–9 a.m. to determine thyroid hormone levels for four rounds, with a duration of eight months between each round. A linear mixed model of the natural log of the individual hormone levels used random intercepts for subjects while controlling gender, baseline age, and body mass index (BMI) was used to compare between conventional and organic farmers or the impact of cumulative days of spraying insecticides, herbicides or fungicides. The estimated marginal means of the thyroid hormone levels (TSH, FT3, T3, and T4) estimated from the linear mixed models were significantly higher among the conventional farmers than organic farmers. As cumulative spray days of insecticide, herbicide or fungicide increased, TSH and FT3 increased significantly. FT4 decreased significantly as cumulative spray days of insecticide or fungicide increased. These findings suggest that the insecticides, herbicides, and fungicides sprayed by conventional farmers exert endocrine-disrupting activities, altering the hypothalamic-pituitary-thyroid (HPT) axis homeostasis.

Environmental Factors Affecting Thyroid-Stimulating Hormone and Thyroid Hormone Levels

“…The effect of various pesticides on TSH and thyroid hormone levels in healthy adults was tested (phenoxybenzoic acid (3-PBA) (metabolite of pyrethroid insecticide), trichloro-2-pyridinol (TCPY) (a metabolite of chlorpyrifos), cis and trans -3-2,2-dichlorovinyl-2,2-dimethylcyclopropane carboxylic acid ( cis and trans -DCCA) (pyrethroid metabolites), 1-napththol (1N) (a metabolite of carbaryl and naphthalene), ethylene bisdithiocarbamate (EBDC) fungicides, insecticide fipronil sulfone metabolite, dithiocarbamate fungicides, lambda-cyhalothrin (pyrethroid), paraquat (herbicide), p , p ′-dichlorodiphenyltrichloroethane (DDT), p , p ′-diphenyldichloroethene (DDE), hexachlorobenzene (HCB), alpha-chlordane, endosulphan 2, methoxychlor, beta-hexachlorocyclohexane (HCH) and mancozeb (fungicide)) ( Table 2 ). Some studies have compared TSH and thyroid hormone levels between conventional farmers (who use pesticides) and organic farmers [ 410 ]. Studies have yielded inconsistent results.…”

“…Studies have yielded inconsistent results. Pesticide use increased [ 341 , 410 , 411 , 412 , 413 , 414 , 415 , 416 , 417 ], decreased [ 415 , 418 , 419 , 420 ] or had no effect [ 352 , 355 , 356 , 413 , 421 , 422 , 423 , 424 , 425 , 426 , 427 , 428 , 429 , 430 , 431 , 432 ] on TSH levels. T4 levels either increased [ 343 , 410 , 412 , 414 , 415 , 416 , 420 , 433 , 434 , 435 ], decreased [ 344 , 410 , 416 , 421 , 422 , 423 , 426 , 427 , 428 , 429 , 433 , 436 ] or did not change [ …”

“…T4 levels either increased [ 343 , 410 , 412 , 414 , 415 , 416 , 420 , 433 , 434 , 435 ], decreased [ 344 , 410 , 416 , 421 , 422 , 423 , 426 , 427 , 428 , 429 , 433 , 436 ] or did not change [ 341 , 352 , 355 , 356 , 411 , 413 , 417 , 421 , 423 , 424 , 425 , 427 , 428 , 430 ] after pesticide use. The same was observed with T3: studies reported an increase [ 343 , 410 , 416 , 420 , 433 , 434 , 435 ], decrease [ 343 , 344 , 414 , 416 , 417 , 429 , 436 , 437 , 438 ...…”

Acute Changes in Thyroid Hormone Levels among Thai Pesticide Sprayers

“…Several epidemiologic studies have established an association between OPs and alterations of thyroid hormone levels [ 8 , 9 ]. A limited number of studies have examined whether ever using OP pesticides was associated with hypothyroidism [ 9 , 10 , 11 ], or whether use in the past growing season was related to alterations in thyroid hormone levels [ 12 , 13 , 14 ]. Experimental animal studies have also shown that organophosphate (OP) disturb thyroid gland function [ 15 , 16 ].…”

“…We have previously shown in the larger longitudinal cohort, from which the farmers in this study were recruited, that after adjusting for covariates, thyroid hormone levels of conventional pesticide using farmers were significantly higher than those of organic farmers. Several specific herbicides had a significant relationship between the amount applied and an increase in thyroid hormone levels [ 12 ], and increasing the cumulative number of spray days of pesticides significantly increases the level of thyroid stimulating hormone (TSH) and free triiodothyronine (FT3) [ 13 ]. These farmers also had significantly higher abnormal metabolic biomarkers, body mass index (BMI), waist circumference, % body fat, triglycerides, total cholesterol, and low-density lipoprotein (LDL) values) compared to the organic farmers [ 36 ], and there was a significant association between the number of days of pesticide spraying and levels of cholesterol, high-density lipoprotein (HDL), LDL, blood pressure and BMI in the longitudinal cohort [ 37 ].…”