Abstract
Currently, 30% to 50% of the population are at risk of vitamin D deficiency in Europe and in the United States. Recently, vitamin D has been enormously cited.
One the one hand, it is because we realize how important it is for health; on the other hand, it is due to the fact that researchers continue to discover new activities of this essential vitamin and its metabolites that have a number of properties of hormones. A good indicator of vitamin D status in the body is plasma calcidiol concentration that reflects vitamin D from food, sun exposure of the skin, and vitamin D conversion from fat deposits in the liver.
Low calcidiol level is associated with a low calcitriol level and lower intestinal calcium absorption, resulting in hypocalcaemia and a secondary increase in the secretion of parathyroid hormone. Decreased vitamin D concentration below 30 nmol/l (12 ng/ml) leads to reduced muscle strength.
Vitamin D reduces the risk of falls in old people by more than 20%. In our elderly population, there is a critical lack of vitamin D, as determined by calcidiol level, and it is one of the causes of senile osteoporosis.
The recommended daily dose of vitamin D of 800 IU daily is capable of improving calcidiol level and reducing serum PTH level as well as increasing muscle strength. Many cells, in addition to renal ones, possess the enzyme 1-alpha-hydroxylase, thus allowing local metabolism of circulating calcidiol.
Moreover, many of these cells have the vitamin D receptor that is responsible for the biological function of the active hormone, i.e. the paracrine role of vitamin D. Outside the kidneys, it acts as a signal molecule between cells, thus controlling approximately 200 genes involved in cell differentiation, replication, and immunity.
Therefore, vitamin D is encountered in conditions caused by an immune disorder, glucose metabolism of the cardiovascular system as well as invasive tumour diseases.