A pineapple pesticide that made its way into milk in Hawaii also made its way into men's brains, and those men were more likely to develop Parkinson's disease, a new study finds.
It's the latest in a very long series of studies linking various pesticides to Parkinson's, which is caused by the loss of certain brain cells.
And the study also seems to support a mystifying observation: smokers seem to be protected against Parkinson's.
For the study, Dr. Robert Abbott of the Shiga University of Medical Science in Otsu, Japan, and colleagues studied 449 Japanese-American men living in Hawaii who were taking part in a larger study of aging. They gave details of how much milk they drank as part of a larger survey, and they donated their brains for study after they died.
The men who drank more than 16 ounces of milk a day had the fewest brain cells in a part of the brain called the substantia nigra, which is damaged in Parkinson's, they reported in the journal Neurology.
The researchers also looked for the pesticide heptachlor, which was taken off the market for most uses in the U.S. in 1988.
"Among those who drank the most milk, residues of heptachlor epoxide were found in nine of 10 brains as compared to 63.4 percent for those who consumed no milk," the researchers wrote.
It's known the milk in Hawaii was contaminated, probably from the feed given to the cattle. "The researchers could not test whether the milk the men drank was contaminated with pesticides (heptachlor, in this case), and no one knows how long or how widespread the contamination was before being detected," the Parkinson's Disease Foundation said in a statement on its website.
"The potential link between drinking milk, pesticides and development of Parkinson's disease needs further investigation," the foundation said.
The men who smoked and who also drank milk showed none of the brain cell loss.
"This study is unique because it brings together two critical but different pieces of information — environmental exposure and physical changes in the brain — to understand potential contributors of Parkinson's disease," James Beck, vice president of scientific affairs at the Parkinson's Disease Foundation, said in a statement.
"For people living with Parkinson's, understanding the impact of environmental factors is crucial as nearly 85 percent have no idea why they developed Parkinson's. There is no clear genetic link," Beck said.
The Parkinson's Disease Foundation estimates that 1 million Americans have the condition, marked by tremor, rigid muscles and problems with movement. There is no cure, although early treatment can delay the worst symptoms.
"For scientists, the opportunity to study brains generously donated by the participants of this study was crucial to establishing a potential link between different environmental exposures and Parkinson's, and will be crucial to solving the disease overall," Beck said.
This article first appeared on NBCNews.com.