Scientists say using DDT against malaria could be fueling global obesity

Could the fight against malaria be making us fat?

That’s what one scientist who studies an increasingly important, if counterintuitive, branch of genetics thinks.

Spraying DDT in Italy, during World War II
Spraying DDT in Italy, during World War II
Flickr, otisarchives4

The pesticide DDT, though banned for use throughout much of the rich world because of its environmental persistence and potential for harm, is still widely used throughout the developing world to fight malaria. On balance, the World Health Organization thinks the health benefit from reducing malaria outweighs – in these countries anyway – the potential health and environmental safety risks of DDT.

Michael Skinner, a geneticist and founder of the Center for Reproductive Biology at Washington State University, thinks the potential harm of DDT needs to be looked at not just in terms of its immediate impact but across generations.

“The potential transgenerational actions of DDT need to be considered in the risk-benefit analysis of its use,” says Skinner.

You probably know that genes make proteins which do the work in living creatures. And that bad genes make bad proteins, which can cause disease or perhaps make us prone to mix plaids or drink red wine with fish … or some other kind of deleterious outcome. Scientists know this as the central dogma of molecular biology and it implies a simple, linear formula in which our genes operate in one deterministic direction.

But science, if it teaches you anything, teaches that what we don’t know is usually much greater than what we do.

It turns out that genetics is not so simple and linear as the central dogma would imply. An increasing body of research in a field known as epigenetics shows that maternal exposure to chemicals that don’t alter DNA can still create damaging alterations that persist and are passed on to later generations.

Skinner is an epigeneticist. He and his colleagues recently published a study in mice for the journal BMC Medicine that indicates DDT can have a powerful effect two generations after exposure. Put another way:

“What your great-grandmother was exposed to during pregnancy, like DDT, may promote a dramatic increase in your susceptibility to obesity, and you will pass this on to your grandchildren in the absence of any continued exposures,” says Skinner.

It was just a mouse study, of course, but the effect was pretty dramatic. Skinner and his colleagues exposed gestating rats to DDT and saw no changes in obesity rates among the exposed parents or first generation offspring. But in the third generation, more than half the offspring were obese. The researchers speculated that DDT alters gene behavior – even though the DNA sequences remain unchanged.

The Skinner lab at WSU has been documenting such epigenetic phenomena for a number of other insecticides or toxic chemicals over the years. But he said they have never seen the kind of trans-generational impact caused by DDT.

Skinner added that it’s been a half century since Rachel Carson’s book “Silent Spring” documented DDT’s effects on the environment and wildlife. The pesticide’s use has since been banned in the U.S. but remains a popular option for fighting malaria in poor countries. His study indicates it is quite possible that the long-term effects of DDT, used to fight one big killer disease, has been quietly fueling the rise of another global killer, obesity.

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Tom Paulson

Tom Paulson is founder and lead journalist at Humanosphere. Prior to operating this online news site, he reported on science,  medicine, health policy, aid and development for the Seattle Post-Intelligencer. Contact him at tom[at]humanosphere.org, follow him on Twitter @tompaulson and/or send a comment below.