AACE: Agent Orange Ups Some Thyroid Risks
By Kristina Fiore, Staff Writer, MedPage Today
Published: April 26, 2010
Reviewed by Dori F. Zaleznik, MD
; Associate Clinical Professor of Medicine, Harvard Medical School, Boston and
Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner
§ Explain that veterans who'd been exposed to Agent Orange were three times more likely to develop Graves' disease, but were not at greater risk of other thyroid disorders including cancer or nodules.
§ Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered preliminary until published in a peer-reviewed journal.
BOSTON -- Vietnam veterans who came in contact with Agent Orange are more likely to develop Graves' disease than those who avoided exposure, researchers said here.
The autoimmune disorder was three times more prevalent among veterans who encountered the dioxin-containing chemical, Ajay Varanasi, MD, of SUNY Buffalo, and colleagues reported at the American Association of Clinical Endocrinologists meeting here.
"We also looked at other [thyroid] diagnoses," Varanasi told MedPage Today, "but we didn't find any significant differences in thyroid cancer or nodules."
Varanasi and colleagues originally hypothesized that the latter two diagnoses may be more prevalent among vets exposed to the toxin.
Agent Orange was a defoliant sprayed from U.S. planes and helicopters during the Vietnam War to deprive Viet Cong and North Vietnamese soldiers of cover. Veterans have long complained that exposure to the chemical caused them a variety of health problems, though few have been confirmed.
Since most Vietnam veterans have been assessed for possible Agent Orange exposure, the researchers were able to review their records and correlate that with disease.
In 2008, they assessed the prevalence of major thyroid diagnoses in the Veterans Affairs (VA) electronic medical record database beginning in 1996 for veterans born between 1925 and 1953 who were treated in a VA network in upstate New York.
They compared the frequency of diagnosis with thyroid cancer, nodules, hypothyroidism, and Graves' disease in both exposed and nonexposed populations.
A total of 23,939 vets had been classified as exposed to Agent Orange, while 200,109 were not exposed.
The researchers found that the prevalence of Graves' disease in those exposed to Agent Orange was three times that of the unexposed group (OR 3.05, 95% CI 2.17 to 4.50, P=0.001).
The relationship remained even after multivariate analyses accounted for potential confounders such as smoking (OR 2.76, 95% CI 2.22 to 3.81, P<0.001).
Interestingly, Varanasi said, prevalence of hypothyroidism was lower in those exposed to Agent Orange. Nor was there any difference in the prevalence of thyroid cancer or nodules between those exposed and those not exposed.
"There's no real mechanism as to why it should cause a high prevalence of cancer," Varanasi said.
But the literature holds a likely mechanism linking exposure to Graves' disease, he added.
"In doing a literature search, we found that the dioxin in Agent Orange might have some immune-modulating effects in human beings," he said.
This dioxin -- 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) -- binds to aryl hydrocarbon receptors (AhR) very tightly, leading to prolonged activation of genomic and nongenomic metabolic disorders, the researchers said.
In mice, for example, AhR can regulate the differentiation of regulatory T cells and of T cells that produce interleukin-17. Also, AhR ligands like TCDD can modulate autoimmunity.
"The effects could be through this hydrocarbon, and this receptor is mainly expressed in T-helper-17 cells," Varanasi said. "Through this mechanism, we could have some immune modulating effects, and this could cause a higher prevalence of Graves' disease in exposed patients."
He and colleagues concluded that the relationship of Graves' disease to Agent Orange exposure warrants further investigation.
The researchers reported no diclosures.
Primary source: American Association of Clinical Endocrinologists
Source reference:
Varanasi A, et al "Are veterans exposed to Agent Orange more likely to get Graves' disease?" AACE 2010; Abstract 1046.
Wednesday, April 28, 2010
AACE: Agent Orange Ups Some Thyroid Risks
