There are an increasing number of studies indicating that a
deficiency in vitamin D may contribute to the onset of neurodegenerative
diseases such as Alzheimer's disease (AD), autism,
depression, Parkinson's disease (PD), schizophrenia and multiple
sclerosis (MS) [158,159]. Neurons strongly express the vitamin D
receptor (VDR) and VDR polymorphisms have been associated with
PD [160], AD [161e164] and have been linked to an age-related
decline in cognition. Increased Ca2þ and redox signalling, which
is a feature of these neurodegenerative diseases [159,165], may
reflect a decline in the proposed role of Vitamin D as a guardian of
these signalling pathways.