Vitamin D, a fat-soluble prehormone, crucially maintains calcium and phosphorus balance. Global concern surrounds its deficiency, prevalent in various populations. While vital for bone health, emerging evidence suggests broader effects beyond bone mineralization. Deficiency links to diverse diseases and higher mortality rates. Supplementation, deemed safe and cost-effective, aims to enhance health, especially in vulnerable groups. Clinical trials often fail to consistently demonstrate positive effects across diseases due to design limitations. This review examines vitamin D's potential mechanisms in discussed disorders, emphasizing trials and meta-analyses. Despite extensive research, addressing challenges remains crucial. Future studies should comprehensively evaluate the vitamin D endocrine system rather than focusing solely on 25-hydroxyvitamin D levels. Employing physiologically relevant dosages, categorizing by achieved vitamin D levels, and ensuring extended follow-up are critical. These strategies will refine our understanding of vitamin D's impacts, particularly regarding supplementation on health outcomes. Overcoming these challenges is vital for effectively gauging the potential benefits of vitamin D supplementation in diverse health conditions.