A pesticide found in milk in the early 1980s may be a Parkinson's disease cause, according to a study published Wednesday in Neurology, the medical journal of the American Academy of Neurology.
The pesticide in question is heptachlor epoxide, found in very high levels in the Hawaiian milk supply of the early 1980s. It was frequently used in the pineapple industry at the time and entered the milk supply when cows were fed pineapple debris.
The study found that nonsmokers who drank more than two cups of milk per day were more likely to develop early Parkinson’s symptoms than those who drank less milk.
The study, which was intended to calculate the effects of aging, tracked 449 Japanese-American male participants with an average age of 54 for over 30 years and until death. Autopsies performed on the willing participants looked at whether they had lost brain cells in the substantia nigra area of the brain; loss of these cells is one of the earliest indicators of Parkinson’s, often occurring decades before actual symptoms appear.
Nonsmoking participants had 40 percent fewer brain cells in the substantia nigra than those who drank less than two cups of milk. "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," according to the study.
Participants who were smokers or had smoked in their lifetimes did not have these decreased brain cells. Previous studies have shown that smokers have a lower risk of developing Parkinson’s than non-smokers.
The link between Parkinson’s disease and dairy is not a new one either, according to study author R. D. Abbott, PhD, with the Shiga University of Medical Science in Otsu, Japan. “This adds to the literature that diet may indeed play a role in Parkinson’s,” said 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.”
It is unclear at this time whether the increased Parkinson’s risk is linked to the dairy itself or to the pesticide, though the scientists did learn that the accumulation of heptachlor epoxide occurred before the cell damage, which makes the link between the pesticide and Parkinson's seem likely.
The researchers were quick to caution against making hasty assumptions based on this data. “There are several possible explanations for the association, including chance,” said Honglei Chen, MD, PhD. “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.”
In addition, the milk drunk by the participants was never tested for this pesticide.
"This study is not a wake-up call to stop drinking milk -- only 12 people who drank about two glasses of milk a day showed significant loss of neurons," said James Beck, vice president of scientific affairs at the Parkinson's Disease Foundation, reports HealthDay. "Nevertheless, its results also suggest that low levels of a pesticide, accumulated in milk, contributed to the loss of brain cells. So a practical question to ask is if it is time to consider strategic purchases of organic foods -- it may be.”
Heptachlor epoxide is no longer used as an insecticide in the United States, except for controlling fire ants in power transformers. It was, however, used during the 1960s and 1970s as a termite killer in homes and on crops such as corn and may still be present in contaminated soil and water.
Around 1 million people in the U.S. have Parkinson’s. There is no cure for the disease.
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Milk image via Shutterstock