The consumption of dairy products, particularly of low fat milk, has been shown to be associated with the occurrence of
Parkinson's disease. This association does not necessarily reflect a pathophysiological role of milk intake in the development of
Parkinson's disease. Nevertheless, the present review discusses a potential mechanism possibly mediating an effect of milk consumption on
Parkinson's disease. The case is made that milk is tailored in part to support bone mineralization of the suckling offspring and is thus rich in
calcium and
phosphate. Milk intake is thus expected to enhance intestinal
calcium phosphate uptake. As binding to
fatty acids impedes Ca2+ absorption, low fat milk is particularly effective.
Calcium and
phosphate uptake inhibit the formation of
1,25(OH)2D3 (1,25-
dihydroxy-vitamin D3 =
calcitriol), the active form of
vitamin D.
Calcium inhibits
1,25(OH)2D3 production in part by suppressing the release of
parathyroid hormone, a powerful stimulator of
1,25(OH)2D3 formation.
Phosphate excess stimulates the release of
fibroblast growth factor FGF23, which suppresses
1,25(OH)2D3 formation, an effect requiring Klotho.
1,25(OH)2D3 is a main regulator of
mineral metabolism, but has powerful effects apparently unrelated to
mineral metabolism, including suppression of
inflammation and influence of multiple brain functions. In mice, lack of
1,25(OH)2D3 and excessive
1,25(OH)2D3 formation have profound effects on several types of behavior, such as explorative behavior, anxiety, grooming and social behavior.
1,25(OH)2D3 is produced in human brain and influences the function of various structures including substantia nigra. In neurons
1,25(OH)2D3 suppresses oxidative stress, inhibits
inflammation and stimulates
neurotrophin formation thus providing neuroprotection. As a result,
1,25(OH)2D3 is considered to favorably influence the
clinical course of
Parkinson's disease. In conclusion, consumption of milk could in theory accelerate the downhill course of neuronal function in
Parkinson's disease. However, substantial additional experimentation is required to define the putative causal role of
1,25(OH)2D3 in the pathophysiology of
Parkinson's disease and its sensitivity to milk consumption.