Vitamin D is an essential micronutrient with diverse and important functions in the body. It is responsible for the regulation of calcium and phosphate metabolism and the function of the musculoskeletal system. It is important for building bones during childhood and maintaining their strength and health in later life. It is also considered to be important in the body's immune response, reduces inflammatory processes, regulates cell growth, affects the mental and cardiovascular health of humans, and plays a role in preventing cancer, and alleviating symptoms of multiple sclerosis and depression. Therefore, lack of vitamin D, among other things, leads to weakening of the skeleton, and loss of bone strength and bone mass, which increases the risk of fractures. In childhood, vitamin D deficiency will cause rickets, while in adults, osteomalacia. The probability of vitamin D deficiency is increased in people who rarely spend time in the sun, wear protective clothing, and use sunscreens, in people with darker skin, obese people, people taking drugs that affect vitamin D metabolism, hospitalized patients, people housed in institutions, elderly people and pregnant women. The high incidence of vitamin D deficiency is a public health problem. Therefore, it is recommended to monitor the value of vitamin D in serum in vulnerable population groups. Prevention and treatment of rickets include vitamin D supplementation, increasing dietary calcium and phosphate intake, and ensuring adequate exposure to sunlight. In the pediatric population, vitamin D supplementation is recommended for all infants, children with limited sun exposure, and those with darker skin. Improving awareness of the importance of vitamin D and its impact on the health of children, as well as the adult population, is essential for the prevention of rickets, osteomalacia, and other diseases associated with a lack of this vitamin.