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 / Updated By Maggie Fox 
 
 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. 
 
 “For people living with Parkinson's, understanding the impact of environmental factors is crucial." 
 
 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. 
 
 “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. 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. ||||| A pesticide that was present in milk in the early 1980s may be linked to signs of Parkinson's disease that are showing up in people today, according to a new study. 
 
 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 loss of brain cells in this area of the brain may be an early sign of Parkinson's disease, and can start decades before any visible symptoms of the disease occur, the researchers said. The study included men whose average age was 54 at the start of the study. 
 
 The link between the higher consumption of milk and the loss of cells in this brain area was not found among the men in the study who had ever smoked cigarettes, the researchers noted. Previous research has shown that people who smoke cigarettes may have a lower risk of developing Parkinson's disease, the researchers said. [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. 
 
 High levels of the pesticide were found in the milk supply in the early 1980s in Hawaii, where the chemical was used for insect control in the pineapple industry. The commercial sale of the pesticide in agriculture was banned in the United States by 1988, according to the U.S. Environmental Protection Agency. However, a related compound can still be used today for controlling fire ants in electrical grid machinery, according to the Agency for Toxic Substances & Disease Registry. 
 
 The researchers noted that they do not have direct evidence that the milk the men drank contained the pesticide. 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. 
 
 In the study, researchers followed about 450 Japanese-American men for more than 30 years until they died, and then performed autopsies on them. They looked at the cells in the substantia nigra, and also measured the amount of the pesticide residue in 116 of the men's brains, according to the study, published today (Dec. 9) in the journal Neurology. 
 
 The findings suggest that diet may play a role in the development of Parkinson's disease, the researchers said. However, the new results do not show a cause-and-effect relationship between the pesticide or milk and Parkinson's disease. Rather, they show there is an association between these factors, they said. 
 
 "The vast majority of milk consumers do not get Parkinson's disease," Abbott told Live Science. 
 
 But Abbott recommended that people should generally be vigilant about eating food that may contain pesticides. 
 
 Dr. Honglei Chen, of the National Institute of Environmental Health Sciences, who was not involved in the study, said that the association found in the study could potentially be explained by mechanisms other than this pesticide actually causing the brain changes. 
 
 Chen, who wrote an editorial on the findings that is also published today in the journal, noted that the men's milk consumption was measured only once at the start of the study. The study assumes that "this measurement represented participants’ dietary habits over time," but this may not have been the case, he said in a statement. 
 
 Follow Agata Blaszczak-Boxe on Twitter. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science. ||||| TIME Health For more, visit TIME Health 
 
 Studies have found a connection between the consumption of dairy products and a higher risk of developing Parkinson disease, the neurodegenerative disorder that affects motor neurons in the brain. While researchers speculated that chemicals found in cows’ milk might be responsible, there was little evidence to detail how dairy products like milk and cheese might be affecting people’s risk of the disease. 
 
 Now, scientists may have uncovered a promising clue. Reporting in the journal Neurology, Robert Abbott, from Shiga University of Medical Science in Japan, and his colleagues took advantage of an environmental scandal in Hawaii in the 1980s to investigate the connection. At the time, an organochlorine pesticide used by pineapple farmers made its way into the milk supply when cows were fed a gruel made in part from the pineapple debris. Coincidentally, there was also a study of heart disease among Japanese-American men begun then that involved more than 8,000 men who were followed from mid-life to death. All provided detailed information about what they ate, including how much milk they drank, and some agreed to donate their brains for research upon death. 
 
 MORE: Diabetes Drugs May Offer Hope for Parkinson’s Disease Treatment 
 
 Abbott and his team studied 449 brains and recorded the density of neurons in specific areas of the brain known to be affected by Parkinson’s. 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 milk drinkers also had residues of specific organochlorines called heptachlor epoxide. 
 
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 Interestingly, by measuring when cells in motor nerve regions died, they also learned that the accumulation of heptachlor epoxide occurred before the cells were damaged, strongly hinting that the chemical was responsible for triggering the changes associated with Parkinson’s. 
 
 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. “We don’t have all the data yet, but we are close to finding the smoking gun here,” he says. “It’s not complete, but it’s very suspicious.” 
 
 Heptachlor epoxide is no longer used as an insecticide in the U.S. According to the Environmental Protection Agency, “nearly all registered uses of heptachlor epoxide have been canceled.” But it tends to be persistent, remaining in soil and water for many years. Abbott also notes that it’s been found in goat and cow milk in Ethiopia and that other organochlorines have been detected in the milk supply in Italy. 
 
 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. What it does mean is that diet and lifestyle risk factors should be considered more deeply. “This adds to the literature that diet may indeed play a role in Parkinson’s,” says Abbott. “But it also tells us that there is more to food than just its nutritional value. There’s contamination, and what’s on that food.” 
 
 For now, there’s no reasons to stop drinking milk. (“I drink a cup of milk every day,” says Abbott.) But he hopes his findings fuel the continued careful look at how chemicals in the environment might be affecting our health, even in indirect and not always obvious ways.
– 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.)