A pesticide found in milk in the early 1980s may be associated with Parkinson’s disease pathology in the brain, according to results of a long-term study published in Neurology.
Dairy products have previously been linked to Parkinson’s disease; however this study specifically looked at the effects of milk that may have been contaminated with heptachlor epoxide, an insecticide heavily used in the pineapple industry in Hawaii where it was found in high concentrations in the milk supply in the early 1980s.
The study, led by Robert D. Abbot, PhD, of Shiga University of Medical Science in Otsu, Japan, and colleagues followed 449 Japanese-American men (average age = 54 years) for over 30 years until death as part of the Honolulu-Asia Aging Study. Upon death, autopsies were performed to see whether neuron loss occurred in the substantia nigra, an area of the brain affected early-on in Parkinson’s disease. The researchers also measured the amount of pesticide residue in 116 brains.
Participant milk intake data was collected from 1965 to 1968. Postmortem exams occurred between 1992 and 2004. The researchers found that nonsmokers who drank more than 2 cups of milk per day had over 40% fewer neurons in the substantia nigra than those who drank less than 2 cups per day (95% confidence interval 22.7%–55.7%, P < 0.001). Pesticide residue was found in 90% of participants who drank the most milk compared with 63% of those who did not drink any milk (P = 0.017). The authors note that milk contamination with the pesticide could not be proven, suggesting that the study results show an association between pesticide or milk intake, but not causality.
Interestingly, there was no association between milk intake and neuron density in participants with a history of smoking.
“There are several possible explanations for the association, including chance,” said Honglei Chen, MD, PhD, of the National Institute of Environmental Health Sciences. Dr. Chen pointed out that “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,” adding to the limitations of the study.