By Amy Norton
Thu Apr 19, 2:35 PM ET
NEW YORK (Reuters Health) - A new study has confirmed a relationship between consuming large amounts of dairy products and an increase in the rate of Parkinson's disease in men, but the reason for this relationship remains a puzzle.
Researchers found that among more than 130,000 U.S. adults followed for 9 years, those who ate the largest amount of dairy foods had an increased risk of developing Parkinson's disease, a disorder in which movement-regulating cells in the brain die or become impaired.
There was a clear pattern seen among men, whose Parkinson's risk increased in tandem with consumption of diary, particularly milk. The results were more ambiguous among women, however.
The findings, which appear in the American Journal of Epidemiology, echo those of earlier studies that found a link between dairy consumption and Parkinson's in men, but not women.
For now, it's not clear what effect, if any, dairy foods might have on women's risk of the disease. Nor is it known why there is a relationship seen in men, 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 out which dairy products might be responsible, and why, according to Chen.
The findings are based on detailed dietary and lifestyle information collected from 57,689 men and 73,175 women who took part in a cancer prevention study. 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 amounts of dairy, the study found. Men in the highest-intake group consumed an average of 815 grams of dairy per day, which is roughly equivalent to three to four glasses of milk; those in the lowest-intake group consumed 78 grams of dairy per day, on average.
Milk, rather than dairy products like yogurt and cheese, explained most of the association, according to Chen's team.
This study and previous ones indicate that calcium, vitamin D and fat are not responsible for the link between dairy foods and Parkinson's disease. One theory is that pesticides or other nerve-damaging toxins present in milk could contribute to Parkinson's disease over time. However, dairy foods would likely be only a small part of most people's exposure to these chemicals, according to Chen.
Furthermore, pesticide residues may also be present in other foods, but no other foods were related to Parkinson's disease risk in this study, the researcher noted.
For now, Chen said there is no reason to shun dairy because of the potential relationship to Parkinson's disease. "Given some of the potential health benefits of dairy foods, people can still enjoy their moderate amounts."
However, the researcher added, since the dairy-Parkinson's link has now been seen consistently in different studies, further research is needed to understand why.
SOURCE: American Journal of Epidemiology, May 1, 2007.
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