The article by Michael F. Holick provides a comprehensive overview of the resurgence of vitamin D deficiency and rickets, a condition that was once eradicated through sensible sun exposure and milk fortification. Vitamin D deficiency, primarily caused by inadequate sun exposure and dietary intake, has reemerged as a global health issue, particularly in children. The review highlights the historical perspective of rickets, its prevention, and the importance of vitamin D in maintaining calcium and phosphorus homeostasis, bone health, and overall well-being. It discusses the photobiology of vitamin D production, the role of vitamin D in calcium and phosphorus metabolism, and the consequences of vitamin D deficiency beyond skeletal issues. The article also addresses the prevalence of subclinical vitamin D deficiency, inherited causes of rickets, and the prevention and treatment strategies, emphasizing the importance of adequate vitamin D intake and sensible sun exposure. Additionally, it explores the noncalcemic effects of vitamin D, such as its role in muscle function, immune system regulation, and the prevention of certain cancers and autoimmune diseases. The conclusion underscores the need for proactive measures to ensure adequate vitamin D levels, particularly during pregnancy and early childhood, to prevent chronic health issues.The article by Michael F. Holick provides a comprehensive overview of the resurgence of vitamin D deficiency and rickets, a condition that was once eradicated through sensible sun exposure and milk fortification. Vitamin D deficiency, primarily caused by inadequate sun exposure and dietary intake, has reemerged as a global health issue, particularly in children. The review highlights the historical perspective of rickets, its prevention, and the importance of vitamin D in maintaining calcium and phosphorus homeostasis, bone health, and overall well-being. It discusses the photobiology of vitamin D production, the role of vitamin D in calcium and phosphorus metabolism, and the consequences of vitamin D deficiency beyond skeletal issues. The article also addresses the prevalence of subclinical vitamin D deficiency, inherited causes of rickets, and the prevention and treatment strategies, emphasizing the importance of adequate vitamin D intake and sensible sun exposure. Additionally, it explores the noncalcemic effects of vitamin D, such as its role in muscle function, immune system regulation, and the prevention of certain cancers and autoimmune diseases. The conclusion underscores the need for proactive measures to ensure adequate vitamin D levels, particularly during pregnancy and early childhood, to prevent chronic health issues.