Calcium is an essential mineral that is one of the main components of bones and teeth. There is more than 1 kg of calcium in the body of an adult, most of which serves structural functions; it is primarily necessary for the hardness of the bones, but without it, we would not be able to move. Many other biological processes also require calcium, such as the contraction of muscles and blood vessels, or the functioning of the nervous system. Calcium also affects hormone production: in the case of its deficiency, the level of some hormones increases. Since a lot of calcium is stored in our bones, our body can regulate it well so that there is always an available amount of it. However, precisely because of this, if someone chronically consumes too little of it, our body will cover the missing part from our bones, so they may weaken over time, which leads to osteoporosis. By itself, calcium supplementation led to quite mixed and disappointing results, but together with vitamin D, it already effectively increased bone density.