SAN DIEGO — Researchers at UC San Diego published a study Tuesday establishing a link between the weed killer Roundup and severe cases of liver disease in humans.

The researchers studied the amount of glyphosate, the main ingredient in Roundup, in the urine samples of two groups of people: one with nonalcoholic fatty liver disease and one without. The study found that glyphosate residue was higher in the urine of subjects with liver disease regardless of possible underlying factors such as age, body mass index or race.

Company representatives could not be immediately reached for comment on the results of the study, which was published in the journal Clinical Gastroenterology and Hepatology.

The UCSD researchers surveyed 93 patients in total, 41 percent of whom were men and 42 percent were white. An additional 35 percent of subjects were Hispanic or Latino.

"There have been a handful of studies, all of which we cited in our paper, where animals either were or weren't fed Roundup or glyphosate directly, and they all point to the same thing: the development of liver pathology," said UCSD professor and study leader Paul Mills. "So I naturally thought: `Well, could it be exposure to this same herbicide that is driving liver disease in the U.S.?"'

Roundup, manufactured by Monsanto, a subsidiary of the German chemical company Bayer AG, has rapidly increased in use since the mid-1990s. During that same period, nonalcoholic fatty liver disease cases in the U.S. have also risen significantly, according to the UCSD researchers.

Glyphosate-based herbicides account for roughly half of Monsanto's annual revenue, and most people are exposed to the chemical by eating non- organic grains like wheat and oats. Glyphosate is currently the most widely used herbicide in the country, according to UCSD.

On Monday, a jury in Alameda County awarded more than $2 billion to a San Francisco Bay Area couple who claimed Roundup caused them to contract non- Hodgkin's lymphoma.

The verdict was the third Roundup-related legal battle Monsanto has lost in California since mid-2018. The company said it plans to appeal the decision, as it has the other two, and maintains that Roundup does not cause cancer or other illnesses.

"Bayer is disappointed with the jury's decision and will appeal the verdict in this case, which conflicts directly with the U.S. Environmental Protection Agency's interim registration review decision released just last month, the consensus among leading health regulators worldwide that glyphosate- based products can be used safely and that glyphosate is not carcinogenic and the 40 years of extensive scientific research on which their favorable conclusions are based," the company said in a statement.

More than 13,000 plaintiffs across the country currently have lawsuits pending against Monsanto.

Mills and the UCSD research team plan to launch further studies into glyphosate's affect on humans. One of those studies includes putting a group of subjects on a strict diet of organic food to track how herbicide-free food may affect the development of liver disease. The researchers also intend to monitor how other herbicides affect human health.

"There are so many synthetic chemicals we are regularly exposed to," Mills said. "We measured just one."