Magnesium is one of the mineral elements essential for proper growth and functioning of the human body. It participates in nerve and muscle function, cardiac excitability, maintenance of normal arterial blood pressure, bone integrity, and glucose–insulin metabolism. Magnesium deficiency is associated not only with disturbances in morphological growth and intellectual maturation of children and adolescents but also with later development of many chronic diseases, including migraine, cardiovascular events (myocardial infarction, stroke), arterial hypertension, type 2 diabetes, and increased susceptibility to the adverse effects of stress. States of normo , hyper and hypomagnesemia were analyzed in the context of the above mentioned disease entities occurring in developmental age. Because meeting daily magnesium requirements from a typical European diet is often difficult, the rationale for supplementation with appropriate galenic forms of this mineral was considered. This applies to all age groups but primarily to children and adolescents during development, with regard to the physical and intellectual maturation noted above. The paper also reviews selected studies on magnesium and chronic diseases, dietary sources of magnesium and supplementation options. The expert analysis supports the conclusion that Mg supplementation is advisable, especially during developmental age.