Exposure to pesticides has been linked to respiratory diseases, infertility, cancer, and a variety of other health problems. Now, a new study completed by Japanese researchers links high levels of a certain pesticide found in milk before the early 1980s with a decline in brain cells and an increased risk of Parkinson’s disease syptoms.

“The link between dairy products and Parkinson’s disease has been found in other studies,” said author of the study R. D. Abbott, of the Shiga University of Medical Science in Japan, in a press release. “Our study looked specifically at milk and the signs of Parkinson’s in the brain.”

For the study, researchers examined 449 Japanese-American men involved in the Honolulu-Asia Aging Study, all with an average age of about 54. They studied the participants for over 30 years and then performed autopsies after their deaths, concentrating particularly on whether they had lost brain cells in the substantia nigra area of the brain. Parkinson’s disease is associated with a decline of brain cells in this region.

In addition to measuring brain cells, the researchers measured the amount of residue from a pesticide called heptachlor epoxide, which had been in the milk supply in Hawaii before and during the early 1980s. They found that nonsmokers who drank more than two cups of milk per day had 40 percent fewer brain cells in the substantia nigra than those who drank less than two cups of milk per day. Strangely enough, the smokers who also drank milk saw no decline in their brain cells, though the researchers aren’t sure why smoking somehow protected them. Past research has shown that years of smoking is linked to a lower risk of developing Parkinson’s, but researchers still aren’t entirely sure what chemicals are at play there.

Before jumping to conclusions, we should take the study with a grain of salt. The researchers don’t know for certain if the milk the participants drank indeed contained any heptachlor epoxide, and the study was only compeleted with a small subgroup of men. Further research will be needed on a much broader scale to better understand the association, which could simply be correlation and not causative, even if past research has clearly linked pesticides to Parkinson’s disease.

“There are several possible explanations for the association, including chance,” said Honglei Chen of the National Institute of Environmental Health Sciences, who wrote an editorial accompanying the study, in the release. “Also, milk consumption was measured only once at the start of the study, and we have to assume that this measurement represented participants’ dietary habits over time.”

The researchers aren’t asking anyone to be afraid of drinking milk; the pesticide in question was removed from U.S. products decades ago. The study is merely an attempt to better understand the mechanisms behind Parkinson’s disease, which affects over 200,000 people in the U.S. every year.

Source: Chen H, Marder K. Milk consumption and the risk of nigral degeneration. Neurology. 2015.