The role of milk protein in increasing risk of Parkinson’s disease

Abstract

I read with interest the finding that total dairy and milkconsumption were significantly correlated with incidenceof Parkinson’s disease (PD) in a large study in Greece [1].However, the component of dairy and milk that mightprovide the link was not identified and the possiblemechanism was not proposed. This letter does both.A study from the Health Professionals Follow-Up Studyidentified milk protein, which is primarily casein, as thecomponent of milk correlated with incidence of PD [2]. Atabout the same time, I also found that milk protein had thehighest correlation (direct) with PD mortality rates in anunpublished 58-country ecological study of dietary factorsin which I separated milk into its components fat, protein,and nonfat milk as well as included many other dietarysupply factors in the analysis.The mechanism whereby casein increases the risk of PDis evidently through reducing serum urate or uric acidconcentrations [3]. Urate or uric acid is a strong antioxi-dant, scavenging superoxide, peroxynitrite and hydroxylradical [4], and has been found inversely correlated withprevalence [4] and risk of PD [5]. Ref. [4] found significantinverse correlations of uric acid with PD disease durationand daily levodopa usage for men but not for women. Thisfinding could help explain the marginally non-significantfinding of PD risk for women compared to men in Ref. [1].