Abstract
Circadian rhythms are extremely important regulators of the whole life. The main regulators are external (so called zeitgebers) deeply influenced by the changes in light and dark cycles.
Internal regulators, represented by hormonal activities and gene expressions are part of bone metabolism too. Diurnal activities of bone resorption are easily documented by cyclic changes of CTx levels.
Rhythmicity is regulated by food and fasting, sleep and its change by night shifts and physical activity. Chronotherapy is important in short-acting drugs, mostly.