Purpose of review: Ageing is a generally known risk factor for cognitive decline and dementia. Underlying mechanisms are expected to be multifactorial, but the exact causes are still elusive. This article reviews the potential role of vitamin D in brain function by presenting an overview of recently published mechanistic, rodent as well as human studies. Recent findings: There is emerging evidence that suggests a beneficial role for vitamin D in brain physiology, for instance by the promotion of neurotransmission, neurogenesis, synaptogenesis, amyloid clearance and the prevention of neuronal death. In addition, several observational studies have shown associations between higher serum vitamin D concentrations and better cognitive performance. To date, imaging studies and randomized controlled trials are scarce, but these studies are expected to fulfil a crucial role towards a better understanding on vitamin D-mediated brain processes in the future. Summary: Despite accumulating evidence supporting a role of vitamin D in brain function, only a handful of human trials have been performed. Consequently, the question whether the association between vitamin D, cognitive decline and dementia is causal cannot be sufficiently answered yet.