There was a clear pattern among men, whose Parkinson risk increased in tandem with consumption of diary, particularly milk. The results are more ambiguous for women, however.
A new study has confirmed a relationship between the consumption of large quantities of dairy products and increased rates of Parkinson's disease in men, but the reason for this relationship remains an enigma.
Researchers found that among more than 130,000 U.S. adults followed for 9 years, those who ate the highest amount of dairy products have an increased risk of developing Parkinson's disease, a condition in which the movement of regulatory cells of the brain die or become impaired.
The results, which appear in the American Journal of Epidemiology, echo those of previous studies that have found a link between consumption of dairy products and Parkinson's disease in men but not women.
For the moment it is unclear what effect, if any, dairy products could have on women's risk of disease. It is not know why there is a relationship in humans, lead study author Dr. Honglei Chen, a researcher at the National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, told Reuters Health.
Larger studies are needed to find dairy products, which could be responsible, and why, according to Chen.
The findings are based on dietary and lifestyle information collected from 57,689 men and 73,175 women who took part in a study on cancer prevention. Over 9 years, 250 men and 138 women were diagnosed with Parkinson's disease.
Men with the highest levels of dairy consumption were 60 percent more likely to develop the disease than those who consumed the least amount of dairy, the study. Men in the highest dose group consumed an average of 815 grams of milk per day, which is roughly the equivalent of three to four glasses of milk, those who have the greatest intake group consumed 78 grams of milk per day on average.
Milk rather than dairy products like yogurt and cheese, explained most of the association, according to Chen's team.
This and previous studies show that calcium, vitamin D and fat are not responsible for the link between dairy products and Parkinson's disease. One theory is that pesticides or other toxins harmful nerve present in milk could contribute to Parkinson's disease over time. However, dairy products would likely be only a small part of most people from exposure to these chemicals, according to Chen.
In addition, residues of pesticides in May also be present in other foods, but no other foods are linked to Parkinson's disease risk in this study, the researcher noted.
For now, Chen said there is no reason to avoid dairy products because of the potential of Parkinson's disease. "Given the potential health benefits of dairy products, people can still enjoy them in moderation."
However, added the researcher, dairy products, from Parkinson's disease link has been seen regularly in the various studies, further research is needed to understand why.