Vitamin D: Meaningful dietary supplement or short lived hormone hype?

People cover most of their vitamin D requirements through exposure to sunlight, as only a few foods, such as wild salmon, are naturally rich in vitamin D. UVB radiation is absorbed through the skin and causes the conversion of 7-dehydrocholesterol to previtamin D3. This is converted into vitamin D3, which is transported to the liver, where it is hydroxylated into 25-hydroxyvitamin D3. The measurement of 25(OH) D3 concentrations is crucial for classifying vitamin D status, which, however, is not yet uniformly defined worldwide. 25(OH) D3 is then transported to the kidneys, where it is hydroxylated to 1,25-dihydroxyvitamin D3. This is the biologically active form and is therefore responsible for calcium homeostasis. Around one billion people are currently affected by vitamin D deficiency. This causes rickets in children and osteomalacia in adults. However, we now know that vitamin D deficiency is also responsible for many extraskeletal consequences, such as an increased risk of developing cancer and multiple sclerosis or suffering from cardiovascular disease.