According to the Environmental Protection Agency (EPA), heptachlor was used from the 1960-70s to kill termites found in the home, and by farmers to kill insects on farm crops, especially corn.
It was phased out from the 1970s, and by 1988, the commercial sale of heptachlor was banned in the US.
Its use is now restricted to controlling fire ants in power transformers.
There is little information available about the health effects on humans from heptachlor epoxide, but the EPA cites animal studies suggesting that long-term exposure can affect the liver and kidneys and cause tremors and convulsions. In rat models, it caused suspected fertility and developmental problems.
Parkinson’s disease is a slowly progressive disorder affecting movement, muscle control and balance. Cell death occurs in the brain, particularly in a cell mass known as the substantia nigra, which is involved in the control of movement and coordination.
Previous studies have found a link between dairy products and Parkinson’s, but this study focused specifically on milk and the signs of Parkinson’s in the brain.
R. D. Abbott, PhD, from the Shiga University of Medical Science in Otsu, Japan, and colleagues followed 449 Japanese-American men who were enrolled in the Honolulu-Asia Aging Study.
Participants, who had an average age of 54, were tracked for more than 30 years until they died.
Autopsies were then performed to find out whether they had lost brain cells in the substantia nigra area of the brain.
This loss is a feature of Parkinson’s disease and can start decades before the onset of symptoms.
Researchers also measured the amount of residue of heptachlor epoxide in 116 brains.
The chemical was found at very high levels in the milk supply in the early 1980s in Hawaii, where it was used in the pineapple industry to kill insects. It was removed from use in the US around that time. It may also be found in well water.
Heptachlor residue and brain cell loss co-occur
Residues of heptachlor epoxide were found in 90% of people who drank the most milk, compared with 63% of those who did not drink any milk.
Nonsmokers who drank more than two cups of milk per day had 40% fewer brain cells in that area of the brain than people who drank less than two cups of milk per day.
Among those who had smoked at some time, there was no association between milk intake and loss of brain cells, supporting previous studies suggesting that smokers have a lower risk of developing Parkinson’s disease.
Limitations include a lack of evidence that the milk participants drank contained heptachlor epoxide. The study does not show that the pesticide or milk intake caused the disease; it only shows an association.
Dr. Honglei Chen, of the National Institute of Environmental Health Sciences and a member of the American Academy of Neurology (AAN), added in a corresponding editorial: “There are several possible explanations for the association, including chance. Also, milk consumption was measured only once at the start of the study, and we have to assume that this measurement represented participant, dietary habits over time.”