where is vitamin d synthesized in the skin
Vitamin D The skin consists of two primary layers: the inner layer called the dermis, composed largely of connective tissue, and the outer, thinner epidermis.[162] Thick epidermis in the soles and palms consists of five strata; from outer to inner, they are: the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. Vitamin D is produced in the keratinocytes[163] of two innermost strata, the stratum basale and stratum spinosum.[160]
Sun tanning By the early 20th century, the therapeutic benefits of sunlight began to be recognised.[26] In 1903, Niels Finsen was awarded the Nobel Prize in Medicine for his “Finsen Light Therapy”.[27] The therapy was a cure for diseases such as lupus vulgaris and rickets. Vitamin D deficiency was found to be a cause of rickets, and exposure to the sun would allow vitamin D to be produced in a person. Therefore, sun exposure was a remedy to curing several diseases, especially rickets. In 1910 a scientific expedition went to the island of Tenerife to test the wider health benefits of "heliotherapy",[28] and by 1913 "sunbathing" was referred to as a desirable activity for the leisured class.[29]