Lack of exposure to sunshine can cause a vitamin D deficiency, which can lead to stunted growth and bone deformities in children (a condition known as rickets), or soft/weak bones (osteomalacia) in adults. Vitamin D helps to regulate calcium and phosphate in the body, which are required for healthy bones, teeth and muscles. Vitamin D is also involved in several signalling pathways, including some within the immune system, and inhibition of tumours. Here is how a little sunshine helps to keep you healthy.
Vitamin D is a group of related fat-soluble molecules, D1 to D5, of which D2 and D3 are the most important. Both are formed in the skin on exposure to ultraviolet (UV) light. For example, vitamin D3 (cholecalciferol) is formed from 7-dehydrocholesterol, which is found in the membranes of epidermal skin cells and absorbs light with wavelengths of between 290 and 315 nanometres (this is in the UVB band of the spectrum). The product from this photoreaction is not very stable, so spontaneously undergoes a rearrangement reaction to form a more stable isomer, cholecalciferol (Figure 1).
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