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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 reported here.

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 , of the University of California San Francisco and the San Francisco VA Medical Center.

They reported their findings at the here.

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).

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 2.18).

"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.

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