A new Neurology study has found a potential association between a pesticide found in milk more than two decades ago and signs of Parkinson’s disease in the brain.

“We are beginning to learn that diet may have a role in Parkinson’s disease (PD),” lead author R.D. Abbott, Ph.D. with the Shiga University of Medical Science in Otsu, Japan, told Bioscience Technology. “In particular, our data suggest that it can be related to an early loss in neurons prior to the onset of PD. Neuron loss in a critical region of the brain that is associated with PD needs to reach critical levels before the classic symptoms of PD can appear. We found that high intake of milk affects this pre-critical phase.”

The study focused on 449 Japanese-American men who participated in the Honolulu-Asia Aging study with an average age of 54.  The men were followed for more than 30 years and autopsies were performed after death.

Abbott said that all 449 men participating in the study were examined for loss of brain cells in the substantia nigra area, which is important for the study of Parkinson’s, and the critical region of the brain mentioned above.  The amount of residue from a pesticide called heptachlor epoxide, was measured in 116 brains.

[pullquote]According to the study, men who were nonsmokers who drank more than two cups of milk per day had 40 percent fewer brain cells in the substantia nigra area than people who drank fewer than two cups per day.  [/pullquote]

The pesticide was used in the pineapple industry in Hawaii and was found at very high levels in the milk supply there in the early 1980s, according to the press release.  It was used to kill insects and was no longer used in the U.S. beginning around that time.

According to the study, men who were nonsmokers who drank more than two cups of milk per day had 40 percent fewer brain cells in the substantia nigra area than people who drank fewer than two cups per day.  There was no association between milk intake and loss of brain cells in smokers.

Of the participants whose brains were examined for residues of heptachlor epoxide, residues were found in 63 percent of those who did not drink any milk, compared to 90 percent of people who drank the most milk.  It is unknown if the milk participants drank contained the pesticide.

Abbott stressed that the study only shows an association, not a cause.

“There are several possible explanations for the association, including chance,” Honglei Chen, M.D., Ph.D., of the National Institute of Environmental Health Sciences, said in a prepared statement.  Chen wrote a corresponding editorial. “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.”

Abbott told Bioscience Technology other limitations of the study include that no women were examined, and the sample only includes Japanese-Americans living in Hawaii. 

“We believe, however, that our findings are likely generalizable since causes of several diseases in our sample have been found to exist elsewhere,” Abott noted. “Milk and dairy products have also been linked to PD in other cohorts including large samples from the U.S. and Europe.  Our sample is also population based. Subjects were not selected because they had certain diseases or conditions.”

Abbott said it’s too early to tell what the next step in research will be, but his team is interested in this area and will continue to pursue the real mechanism between milk (and other dietary factors) and the risk of Parkinson’s.