Drinking a glass or two of milk a day may raise the risk of Parkinson's disease in middle-aged men, research suggests.
Milk contains many beneficial nutrients
Researchers say the apparent link is unlikely to be due to calcium - milk's key nutritional ingredient.
But they say it is unclear whether another ingredient, or a contaminant may raise the risk of Parkinson's - which overall still remains low.
The study, led by Korea University, is published in the journal Neurology.
Parkinson's disease is a degenerative disease of the nervous system associated with trembling of the arms and legs, stiffness and rigidity of the muscles and slowness of movement.
Previous research has also suggested a link between high consumption of dairy products and a raised risk of Parkinson's in men - but not women.
The latest study focused on 7,504 men aged 45 to 68, who were enrolled in a heart study in Hawaii.
During the course of the 30-year study, 128 developed Parkinson's.
The researchers found those men who consumed more than 16oz (473ml) of milk a day were 2.3 times more likely to develop Parkinson's than those who drank no milk at all.
Overall, the risk of Parkinson's - even among men who drank a lot of milk - was low.
The researchers calculated that in each 12 month period 6.9 cases of Parkinson's could be expected per 10,000 people who drank no milk.
Among those who drank more than 16ozs a day the figure was 14.9 per 10,000.
However, they found no evidence of a link between calcium consumption and Parkinson's.
Robert Meadowcroft, of the Parkinson's Disease Society, said: "This research is still at a very early stage and further work needs to be carried out into the actual components in the milk and dairy products that appear to be influencing the development of Parkinson's."
Rebecca Foster, a nutrition scientist at the British Nutrition Foundation, warned against cutting milk from the diet.
She said: "Milk and milk products (such as cheese and yogurt) are important sources of essential nutrients in diet, including protein, B vitamins such as riboflavin and B12, and minerals such as calcium, zinc and magnesium.
"For example in the UK milk and milk products provide 43% of calcium intake, providing 33% of riboflavin intake and 35% of iodine intake in men and 42% in women."