Vitamin D and sun exposure

Written by: Ana Vrbanović, MD

Vitamin D is important for maintaining the health of bones, the cardiovascular system, reproductive system and preventing infections and skin cancer.

Vitamin D exists in two main forms: D2 (ergocalciferol) and D3 (cholecalciferol). Vitamin D3 is created in the skin during exposure to sunlight (UV radiation). There are two main sources of vitamin D: exposure to sunlight and oral intake through food or through supplements. A lot of factors affect the status of vitamins in the body, such as Fitzpatrick skin type, sex, body mass index, body activity, alcohol consumption and genetic predisposition. Today there is a trend towards low vitamin D concentrations in the body due to increased awareness of the harmfulness of UV rays and use of different methods of protection against sun rays.

Everyday sunscreen protection reduces its concentration and may lead to hypovitaminosis. Yet frequent exposure to UV radiation is dangerous due to the rays’ carcinogenic properties. Oral intake contributes to maintaining an adequate status of vitamin D in individuals diagnosed with a deficiency, which can be discovered by measuring the 25-hydroxy vitamin D concentration (25-OH D) in blood.

Protection against sunlight is recommended by the majority of dermatologists in the world because it slows down skin aging, development of carcinoma and photosensitive disorders. However, exposure to sun rays is an important determinant of vitamin D status in the body. It has been proven that reduced vitamin D concentrations are connected to several dermatological diseases such as atopic dermatitis, psoriasis, mycosis fungoides, systemic lupus, systemic sclerosis and alopecia. Atopic dermatitis, a frequent inflammatory skin disease, exhibits clinical improvement when a vitamin D supplement is given as an addition to classic dermatological therapy. In the case of psoriasis, there is a proliferation of keratinocytes along with infiltration of inflammatory cells in the epidermis and dermis. Vitamin D product controls proliferation of keratinocytes and blocks secretion of inflammatory mediators which reduce infiltration of immune cells. This alleviates the skin symptoms of psoriasis. Reduced vitamin D levels are also monitored in persons suffering from systemic sclerosis and erythematosus lupus. Vitamin administration in therapeutic purposes in the case of these diseases is still being researched.

As already mentioned, vitamin D products reduce proliferation of keratinocytes, improve DNA repair and reduce certain harmful effects of UV rays on DNA. Research has been conducted on the correlation with melanoma and has shown that, with adequate supplement, invasion of the tumour is slowed down. There are certain opposing studies relating to therapeutic prescription of vitamins as part of cancer treatment, but supplementing vitamin D within reference values is considered favourable.

Apart from the fact that vitamin D has a beneficial effect on the skin’s health it also has antimicrobial properties, especially in viral diseases of the upper respiratory tract or mononucleosis. It also has a positive effect on bone health. It is recommended to keep vitamin D at sufficient levels through responsible sun exposure with adequate SPF protection and oral intake if there is a vitamin deficiency. This contributes to skin health and regeneration. If you use a sunscreen daily on all exposed body parts and do not eat food rich in vitamin D, in order to ensure good health, it is recommended to check your vitamin D levels.

Intoxication by vitamin D is rare but may lead to heart arrhythmia and neurological disorders so it is definitely not recommended to take supplements on your own but only following the advice and instructions of an adequate medical expert. Every deficiency should first try to be improved through a proper and balanced diet.

Source: Kechichian, E. & Ezzedine, K. Am J Clin Dermatol (2018) 19: 223. https://doi.org/10.1007/s40257-017-0323-8

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