Several epidemiological studies on large cohorts the United States, Finland and Greece have consistently reported an association between milk intake and a higher incidence of Parkinson’s disease. Pesticide contamination of milk and milk’s urate-lowering effects have been suggested as risk factors to explain epidemiological data.
Overall, the association between Parkinson’s and milk was stronger than the association with other dairy products such as cheese, yogurt, or butter.
Time magazine reports on how scientists may have uncovered a promising clue about the association. Reporting in the journal Neurology, Robert Abbott, from Shiga University of Medical Science in Japan, and his colleagues took advantage of an environmental scandal in Hawaii in the 1980s to investigate the connection.
At the time, an organochlorine pesticide used by pineapple farmers made its way into the milk supply when cows were fed a gruel made in part from the pineapple debris. Coincidentally, there was also a study of heart disease among Japanese-American men begun then that involved more than 8,000 men who were followed from mid-life to death. All provided detailed information about what they ate, including how much milk they drank, and some agreed to donate their brains for research upon death.
Abbott and his team studied 449 brains and recorded the density of neurons in specific areas of the brain known to be affected by Parkinson’s.
The researchers found that men who reported drinking more than two glasses of milk a day (16 oz) showed the thinnest nerve networks in these areas, suggesting compromised function of these nerves, compared to men who drank little or no milk. The milk drinkers also had residues of specific organochlorines called heptachlor epoxide.
They learned that the accumulation of heptachlor epoxide occurred before the brain cells were damaged, strongly hinting that the chemical was responsible for triggering the changes associated with Parkinson’s.
Heptachlor epoxide is no longer used as an insecticide in the U.S., but it tends to remain in soil and water for many years. Abbott notes that it’s been found in goat and cow milk in Ethiopia and that other organochlorines have been detected in the milk supply in Italy.