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Vitamin D, a fat-soluble secosteroid traditionally recognized for skeletal health, exerts pleiotropic effects on cardiovascular physiology and disease. Circulating 25-hydroxyvitamin D [25(OH)D], the principal biomarker of vitamin D status, is frequently suboptimal worldwide, particularly in older adults, individuals with darker skin pigmentation, and populations at higher latitudes. Observational studies consistently associate low 25(OH)D concentrations with increased risk of hypertension, atherosclerosis, myocardial infarction, heart failure, arrhythmias, stroke, and cardiovascular mortality. Mechanistic investigations have revealed that vitamin D modulates cardiomyocyte calcium handling, endothelial function, vascular smooth muscle proliferation, inflammation, oxidative stress, and renin-angiotensin-aldosterone system activity, establishing biologically plausible links to cardiovascular outcomes. Despite these associations, large randomized trials of vitamin D supplementation have failed to demonstrate reductions in major cardiovascular events, likely due to heterogeneity in baseline status, dosing regimens, intervention timing, genetic variability, and underlying comorbidities. Vitamin D may function more effectively as a biomarker of cardiovascular risk rather than a universal therapeutic agent, with deficiency reflecting systemic vulnerability rather than acting as a dominant causal factor. Emerging evidence supports precision approaches targeting individuals with severe deficiency, high renin activity, early endothelial dysfunction, or specific genetic profiles, potentially in combination with lifestyle or pharmacologic interventions. Future research should focus on defining optimal dosing strategies, intervention timing, and mechanistic biomarkers to identify subpopulations most likely to benefit, integrating vitamin D therapy into multifaceted cardiovascular prevention frameworks. This systematic review synthesizes molecular, observational, and clinical trial evidence, critically evaluating the current understanding of vitamin D in cardiovascular medicine and highlighting opportunities for targeted, personalized interventions. Vitamin D represents a complex, context-dependent modulator of cardiovascular health, offering both prognostic insight and potential therapeutic value when appropriately applied.