TUESDAY, Oct. 24, 2017 (HealthDay News) -- Levels of the herbicide Roundup in human urine have increased dramatically among California residents in the past two decades, a new study reports.
Roundup (glyphosate) is used to protect genetically modified corn and soy crops from weeds and also is used on wheat and oats, said the study's lead author, Paul Mills. He is a professor of family medicine and public health at the University of California, San Diego.
Urine collected from 100 Californians between 1993 and 2016 show that glyphosate levels have gone up with the advent of genetically modified crops, Mills said.
In the early samples, "there were very low levels -- they were only detectable in 12 out of 100 people," Mills said. "Then over the next 22 years, we found about a 1,000 percent increase in the levels found in the 100 people, on average."
However, the study does not show that exposure to glyphosate directly caused any health problems in these people, noted Dr. Nima Majlesi, director of medical toxicology at Staten Island University Hospital in New York City.
"I think these studies have a huge flaw in that they really haven't shown any adverse outcomes in human beings," Majlesi said. "All you're seeing is numbers."
Some strains of corn and soy have been genetically altered to render them immune to Roundup, allowing farmers to spray the herbicide without fear of damaging their crops. However, there's some scientific dispute regarding Roundup's potential hazard to humans.
In 2016, the World Health Organization concluded that "glyphosate is unlikely to pose a carcinogenic risk to humans from exposure through the diet." In July, though, California became the first U.S. state to add glyphosate to its list of known carcinogens.
For the study, Mills and his colleagues made use of urine samples that had been collected and preserved for years as part of a long-term study of healthy aging. They tested those along with fresh samples in 100 people for the presence of both glyphosate and aminomethylphosphonic acid (AMPA), an organic chemical produced when the body processes glyphosate.
Average glyphosate levels in urine increased from 0.024 parts per billion in the 1993-1996 samples to 0.314 parts per billion in the 2014-2016 samples, the researchers found.
The average levels in the newer samples reached as high as 0.449 parts per billion after the researchers excluded people with non-detectable levels of glyphosate.
Glyphosate, widely used in residential landscaping, has been found in drinking water, but Mills believes the levels in human urine increased mainly from people eating foods exposed to the herbicide.
"It's unlikely that all these folks are spraying that much Roundup in their yards every day, to get the levels we observed," he said.
Though the study focused on Californians, Mills noted that Roundup is "the most widely used chemical herbicide in the world" and that similar results would probably be found across the United States.
"Our research is showing that a lot of us across the U.S. likely have fairly significant levels of these compounds, unless we take up an organic diet," he said.
Mills noted that animals fed low doses of glyphosate have wound up with liver damage akin to fatty liver disease, adding that "we could have found a signal why so many people are having this increase in liver disease."
However, Majlesi said that the increased glyphosate levels detected in the study are tiny.
"Even though they've gone up, you're talking about miniscule amounts in the urine that mean very little, clinically," he said. "There are levels that are rising, but what do those levels mean? I think that's where people start to over-interpret data."
Mills said his team does have medical data on the people in the study, and in their next phase of research the researchers will examine whether exposure to Roundup has caused any health problems.
In the meantime, both Mills and Majlesi said that people concerned about exposure to glyphosate should consider buying certified organic foods.
"Wash your fruit, and be aware of the fact that if you're not buying organic, it probably is protected by glyphosate," Majlesi said.
The study was published Oct. 24 in the Journal of the American Medical Association.
The National Pesticide Information Center has more about glyphosate.