Veterans exposed heavily to the defoliant Agent Orange during the Vietnam War appear to suffer from a higher rate of diabetes than nonexposed veterans. The findings, reported in next month's issue of the journal Epidemiology, are the first evidence of a link between diabetes and exposure to the herbicide or its contaminant, dioxin. Experts caution, however, that the connection is far from proven.
A group led by statistician Joel Michalek of the Armstrong Laboratory at Brooks Air Force Base in Texas measured current blood dioxin levels in male veterans of Operation Ranch Hand--the unit responsible for spraying Agent Orange in Vietnam from 1962 to 1971. Dioxin levels are a proxy of Agent Orange exposure, as the chemical remains stored in fat cells long after other constituents of the herbicide have disappeared from the body. The subjects' dioxin levels, the researchers found, were 10 to 40 times higher than those of 1276 male veterans who had no contact with the herbicide.
More disturbing, however, Michalek's group found that veterans with the highest dioxin levels were up to 2.7 times more likely than controls to develop diabetes, and they first showed symptoms of the disease, such as impaired glucose tolerance, 3 years earlier on average. Michalek says he can't conclude that dioxin or another Agent Orange component actually causes diabetes--unidentified environmental factors encountered by Ranch Hand vets may have been the real culprit. And it's unclear what kind of biochemical mechanism could account for such a link.
Other experts say it's hard for contemporary studies to pin any health effects in Vietnam veterans on dioxin, as only those with very high exposure will still have detectable blood levels. Indeed, the Ranch Hand and similar ongoing medical studies may have a different value altogether: They may indicate illnesses for which all veterans may have an elevated risk, says Han Kang, director of Environment and Epidemiology Services at the Department of Veterans Affairs. Michalek's group, for one, is now probing for links between Agent Orange exposure in Vietnam veterans and other medical complaints such as cancer and heart disease.