Middle-aged men who drink a glass or two of milk each day may be increasing their risk of developing Parkinson's disease later in life, new research suggests. The ingredient or possible contaminant in milk responsible for this effect is unclear, but the current findings suggest it's not the calcium.

The new findings, which appear in the medical journal Neurology, support those of an earlier report linking high consumption of dairy products with an elevated risk of Parkinson's disease among men, but not women.

The current study involved 7504 men, who were enrolled in the Honolulu Heart Program between 45 and 68 years of age and followed for 30 years for the development of Parkinson's disease. Dietary intake for all subjects was recorded when the study began in the late 1960s.

A total of 128 participants developed Parkinson's disease during follow-up, Dr. R. D. Abbott, from the University of Virginia Health System in Charlottesville, and colleagues note.

The risk of Parkinson's disease increased as the amount of milk consumed each day rose. The final statistical analysis showed that heavy milk drinkers were 2.3-times more likely to develop Parkinson's disease than non-milk drinkers.

Still, even among heavy milk drinkers, the risk of Parkinson's disease was very, very small. The team calculates that, over a period of a year, 6.9 cases of the disease would be expected among 10,000 people who drank no milk each day. By contrast, 14.9 cases would be expected if each of those 10,000 people drank more than 16 ounces per day.

The authors found no evidence that calcium, either from dairy or non-dairy sources, had any effect on the risk of Parkinson's disease. This suggests that some other component of milk is responsible for the pattern seen. Further studies are needed to determine exactly what this ingredient might be, the researchers note.

SOURCE: Neurology, April 2005.