Recent Advances in Fucoidan Bioactivity and Its Molecular Mechanisms in the Intervention of Vascular Cognitive Impairment

Fucoidan is a class of sulfated polysaccharides primarily derived from marine organisms, particularly brown algae and some marine invertebrates. Owing to its structural diversity and broad spectrum of biological activities, including immunomodulatory, anti-inflammatory, antioxidant, vascular protection, anticoagulant, and neuroprotective effects, fucoidan has attracted increasing attention as a promising candidate for functional foods and pharmaceutical applications. This review systematically summarizes the sources and distribution of fucoidan, modern extraction and preparation strategies, chemical structural characteristics, and structure–activity relationships. The biological activities and potential mechanisms of action of fucoidan were the primary focus of this study. Furthermore, this review provides an overview of the molecular mechanisms underlying the protective effects of fucoidan against vascular cognitive impairment. These mechanisms mainly involve the inhibition of NF-κB- and MAPK-mediated neuroinflammatory responses, activation of the Nrf2/HO-1 antioxidant pathway to alleviate oxidative stress, regulation of microglial polarization, maintenance of blood–brain barrier integrity, promotion of neurotrophic factor expression, modulation of autophagy and apoptosis-related pathways, and attenuation of microvascular damage induced by chronic cerebral hypoperfusion through VEGF signaling. Given its multi-target and multi-pathway regulatory properties, fucoidan exhibits promising potential for the prevention and management of vascular cognitive impairment and related neurodegenerative disorders.