Vitamin K Properties in Stroke and Alzheimer's Disease: A Janus Bifrons in Protection and Prevention

Vitamin K is essential for many physiological processes, including coagulation, bone metabolism, tissue calcification, and antioxidant activity. Vitamin K vitamers are represented by lipophilic compounds with similar chemical structure (i.e., phylloquinone (vitamin K1) and menaquinone (vitamin K2)). Vitamin K deficiency can affect coagulation and vascular calcification, increasing the risk of hemorrhages, atherosclerosis, cerebrovascular diseases, and neurodegeneration. Recently, several studies have hypothesized a possible dual role of vitamin K vitamers in benefiting both vascular and cerebral health, e.g., by sphingolipids biosynthesis or ferroptosis inhibition. The aim of this narrative review is to deepen the understanding of biological activities of vitamin K and its possible dual protective/preventive actions in neurovascular and degenerative conditions, e.g., stroke and dementia. Given the difficulties related to hemorrhagic risk entailed in the prevention of strokes, the function of vitamin K antagonists is also investigated. Finally, we track the development of a clinical concept for a future preventive strategy and innovative use of vitamin K as a supplement to counteract neurovascular and pathological processes, focusing in particular on stroke and dementia.