The top photo shows a mangrove forest about 60 miles from Saigon, Vietnam. The bottom photo is of a mangrove forest in 1970, sprayed with the chemical defoliant Agent Orange by the the U.S. Air Force in 1965. The dark spots are some surviving trees.

Is Agent Orange responsible for disease and birth defects in the children of Vietnam War veterans?

For Stefanie Wilderdyke of Adel, Iowa, the answer seems obvious. She and her sister have suffered a staggering array of health problems — lupus, fibromyalgia, Raynaud’s disease (which causes numbness and coldness in the extremities), Sjogren’s syndrome (an immune system disorder), hypothyroidism and endometriosis.

“My sister and I always wondered, with our dad having served in Vietnam, why is this happening?” she said.

But for scientists, the answer is: We don’t know.

In part that’s because there hasn’t been much research into what are called “paternally mediated” birth defects. But scientists also say it’s hard to determine the effects of Agent Orange exposure.

For example, it is nearly impossible to measure how much of the herbicide any single service member received, said Dr. Kenneth Ramos, who headed a congressionally mandated committee reviewing Agent Orange research. The service members moved around so much.

Dioxin has a half-life of seven to 11 years, so it is mainly gone from veterans’ bodies after more than four decades. And no one thought to measure soldiers’ dioxin levels before and after their tours in Vietnam, making current measurements of little value.

“There’s no baseline data,” Ramos said. “You’re trying to reconstruct when you really have no clue what happened.”

Dioxin also occurs naturally in the environment, emitted into the atmosphere by forest fires or backyard burning. People also ingest dioxin from meat or dairy products.

“Unfortunately, dioxin is ubiquitous,” said Dr. Ralph Erickson, the VA’s chief consultant for post-deployment health services. “It’s in a lot of places. We’ve sort of slimed our planet.”

There is clear evidence that the use of dioxin-laden Agent Orange in Vietnam is linked to the health problems of veterans. But the health effects are less certain for subsequent generations.

Scientists aren’t sure, biologically speaking, how male veterans could pass along dioxin to their children and grandchildren.

“When a woman is exposed to some sort of environmental agent, all of her eggs are already present in her ovaries,” Erickson said. “For the men, sperm regenerates every three to four days.

“The biological plausibility is not the same,” he added.

Many of the diseases linked to Agent Orange also have other causes. Ischemic heart disease — hardening of the arteries — is also linked to smoking and poor diet. Type 2 diabetes is connected to Agent Orange exposure, but can also result from obesity.

“It’s easy to generalize the observations in light of all that we don’t know about environmental exposure,” Ramos said. “You would have to get rid of all the smokers, all the drug users, all the environmental stressors in order for you to say that Agent Orange did it.”

In addition, genetics alone — the passing along of a genetic blueprint from parent to child — can’t account for male veterans passing diseases or birth defects connected to Agent

Orange to their offspring.

Little is known about how environmental hazards such as Agent Orange act on genes to cause diseases or birth defects. Some researchers believe the emerging field of epigenetics may offer a clue. It examines the chemical processes that act on the genome, switching genes on and off over time.

“Epigenetics opens the door for the biological basis for paternal inheritance,” Ramos said. “If there’s a possibility that this could happen, then we should investigate.”

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