For Vietnam vets, defoliant exposure 'may exacerbate effects of other risk factors.'
WASHINGTON -- Exposure to Agent Orange during the Vietnam
War doesn't seem to increase the risk of dementia on its own,
but it may exacerbate the effects of other risk factors like PTSD, researchers
In an analysis of Veterans Affairs
data, having been exposed to Agent Orange and having PTSD together was
associated with a significantly increased risk of dementia (hazard ratio 1.67,
95% CI 1.27 to 2.18), according to Deborah Barnes, PhD, MPH, of the University of
California San Francisco and the San Francisco VA Medical Center.
Some 8% of veterans were exposed to
Agent Orange during the Vietnam War, where it was used as an herbicide to clear
dense areas of forest.
It comprised two major ingredients:
2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid
(2,4,5-T); dioxin was an unintended contaminant, as it's highly toxic and a
known human carcinogen.
Many other studies have looked at
the health effects of Agent Orange exposure, and there have been mixed results
regarding its neurological effects. Some studies found no adverse neurologic
effects, while several recent studies have found worse cognitive function with
greater exposure. Other studies have shown that verbal memory is the most
affected neurocognitive region among Vietnam veterans.
Yet there haven't been any studies
specifically looking at the relationship between Agent Orange and the risk of
dementia among these veterans, Barnes said.
Consequently, she and colleagues
accessed VA electronic medical record data on 46,737 Vietnam veterans over age
55 who had at least one baseline visit and one follow-up visit, and who did not
have dementia at baseline.
They looked at Agent Orange exposure
alone and in combination with PTSD. They used Fine-Grey proportional hazards
models to account for competing risk of death.
Barnes noted that there was a
significant difference between the exposed and unexposed populations at
baseline. Veterans exposed to Agent Orange were younger and had more
comorbidities including diabetes, hypertension, cerebrovascular disease,
depression, and PTSD (P<0 .001="" span="">0>
In an unadjusted analysis, the
researchers found that having been exposed to Agent Orange was associated with
an increased risk of dementia (HR 1.31, 95% CI 1.15 to 1.51).
However, that risk disappeared in
unadjusted models, Barnes said.
When they looked at PTSD and
dementia risk, however, they did find a significant association (HR 1.33, 95%
CI 1.10 to 1.62) -- and having both Agent Orange exposure and PTSD together was
associated with a larger increase in risk of dementia (HR 1.67, 95% CI 1.27 to
"Agent Orange alone doesn't
appear to increase the risk of dementia," Barnes said, "but it may
exacerbate the effects of other risk factors such as PTSD."
She cautioned that the findings were
limited because the researchers weren't able to measure the actual exposure to
Agent Orange; they had to rely on patients' own reports of exposure. Future
studies should aim for verification of exposure, she said.