MORE: Taking Care: An Intimate Look at How Parkinson’s Disease Has Changed 1 Family’s Life 
 
 Abbott says that he and his team did not have samples of the milk the men drank, so can’t say for sure that the contaminated milk was the source of the pesticides they found in the mens’ brains, but it’s a reasonable explanation. MORE: Here’s Which Produce Has the Most Pesticides 
 
 The data certainly don’t mean that anyone who drinks several cups of milk a day is putting themselves at risk of developing Parkinson’s. However, they "just have no other explanation for how heptachlor epoxide found its way into the brains of men who consumed milk," said study author Robert D. Abbott, of the Shiga University of Medical Science in Otsu, Japan. “For people living with Parkinson's, understanding the impact of environmental factors is crucial." The researchers looked at Japanese-American men in Hawaii, where the pesticide was frequently used, and found that those who drank more than two cups of milk daily at the start of the study had 40 percent fewer brain cells in an area of the brain called the substantia nigra 30 years later, on average, compared with similar men who drank less than two cups of milk per day. The commercial sale of the pesticide in agriculture was banned in the United States by 1988, according to the U.S. Environmental Protection Agency. [10 Things You Didn't Know About the Brain] 
 
 The researchers also found that residues of the pesticide, called heptachlor epoxide, were present in the brains of 90 percent of the men who drank the most milk, compared with 63 percent of those who did not drink any milk. "The potential link between drinking milk, pesticides and development of Parkinson’s disease needs further investigation," the foundation said. They found that men who reported drinking more than two glasses of milk a day (16 oz) showed the thinnest nerve networks in these areas, suggesting compromised function of these nerves, compared to men who drank little or no milk. “The potential link between drinking milk, pesticides and development of Parkinson’s disease needs further investigation.” 
 
 "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.
– Scientists are urging people to watch what they eat—and drink—in a new study linking a pesticide with Parkinson's disease. Researchers note that, for a time, cattle in Hawaii were likely fed a gruel containing traces of heptachlor, used by American pineapple farmers before it was banned in 1988, per Time. The cows' milk was contaminated, but "no one knows how long or how widespread the contamination was before being detected," the Parkinson's Disease Foundation says, per NBC News. To test the possible effects, researchers studied the brains of 116 Japanese-American men in Hawaii who had given information about their milk-drinking habits before they died. They found men who consumed more than two glasses of milk, or 16 ounces, daily had 40% fewer brain cells in the substantia nigra, an area that shows damage in Parkinson's cases, compared to men who drank less than two cups per day. Some 90% of heavy milk drinkers also had heptachlor residue in their brains, compared to 63% of those who didn't drink milk. Researchers dated the cell damage to after the accumulation of heptachlor, which suggests the chemical was responsible for the changes. The team couldn't test milk samples, but they "have no other explanation for how heptachlor epoxide found its way into the brains of men who consumed milk," a study author tells Live Science. He notes "the vast majority of milk consumers do not get Parkinson's disease," but "this adds to the literature that diet may indeed play a role." The study also backs others suggesting smokers enjoy protection against Parkinson's: Milk drinkers who smoked showed no brain cell loss. One critic notes participants divulged how much milk they drank some 30 years before they died, so their consumption perhaps changed. (This pesticide has been linked to Alzheimer's.)