[Vitamin D and Alzheimer's disease: from an intriguing idea to a therapeutic option].

Beyond the classically described regulation of calcium and bone metabolism, vitamin D is a neurosteroid hormone essential to neurophysiological function (regulation of neurotransmitters and neurotrophins) with anti-inflammatory and antioxidant neuroprotective action. In contrast, hypovitaminosis D, which is extremely frequent in the elderly, may result in neurological dysfunction and may explain part of the cognitive disorders in this population. Epidemiology is consistent with this notion and has repeatedly shown an association between hypovitaminosis D and cognitive decline, either in the general population or in Alzheimer's patients. Preliminary intervention trials confirm the causal relationship and quantify the cognitive effect of vitamin D supplementation in the elderly. This raises prospects for primary/secondary prevention of cognitive decline by exogenous supplies of vitamin D. In particular, although current anti-dementia drugs are only symptomatic, future treatment options could rely on drug combinations preventing several neurodegenerative mechanisms at once. As such, vitamin D enhances the efficacy of memantine in terms of neuronal protection and prevention of cognitive decline in Alzheimer's disease.