Why is it important?
Vitamin D is essential for phospho-calcium metabolism and bone density. Its deficiency is related to ricketism, cardiovascular diseases, autoimmune diseases and mental illnesses.
What is its relationship with cancer?
In recent years, its deficiency has also been linked to an increase in the incidence of some cancers or to a worse prognosis of them, although neither a direct cause nor an improvement has been found through treatment with this vitamin.
How is it obtained? What relationship does it have with the skin and the sun?
10% is obtained through dietary intake, the remaining 90% is synthesized in the skin thanks to the action of ultraviolet B (UVB) radiation. Ultraviolet A radiation has no action on the synthesis of vitamin D. The sun emits UVB and UVA radiation. Tanning booths emit practically only UVA.
What influences vitamin D synthesis?
The amount we have in the body varies according to the following parameters: diet, season of the year, time of day, climate, pollution, geographical location, reflective surfaces, lifestyle, outdoor activity, photoprotection, dietary supplements, skin type and age.
Which sources of UV radiation are the most common?
The sun emits UVB and UVA radiation; tanning machines or booths emit 95-98.5% of UVA, with the amount of UVB being negligible. For this reason, “doing UVA” does not have any beneficial effect on the body as far as vitamin D is concerned.
Is UV radiation dangerous?
UV radiation (both A and B) is the main risk factor for skin cancer, in any of its forms: basal cell carcinoma, squamous cell carcinoma and melanoma. UVA machines are classified, according to the WHO, as first-degree carcinogens. Exposure to UVA booths before the age of 35 increases the risk of melanoma by 75%. Melanoma is not the most common skin cancer, but it is the cause of 75% of deaths from skin cancer.
So, is UVA radiation more dangerous than UVB radiation?
UVB radiation causes inflammation, burns and increases the incidence of skin cancer, as it is mutagenic (damages the DNA of cells). UVA does not normally cause burns, although it is pro-inflammatory and is also mutagenic.
How much do you need per day?
It is estimated that about 1,000-2,000 international units (IU) of vitamin D per day are needed to meet the body’s needs and reduce the risk of diseases related to its deficiency in European latitudes.
How long do I have to be at the beach to make enough?
Sun exposure to a single minimum erythematogenic dose (DEM) in a bathing suit is equivalent to the intake of 10,000 IU/day of this vitamin. A DEM is the amount of solar radiation needed to turn red. Just before turning red from the Sun we have synthesized more than enough for 10 days. In fact, accumulating UV radiation beyond erythema deactivates the radiation we have formed in the skin and from then on has no metabolic value. The cutaneous synthesis of vitamin D is only effective below erythema (redness).
If I don’t sunbathe, how much should I get?
It has been calculated that the maximum sun exposure needed to synthesize enough vitamin D for a Fitzpatrick phototype II is as follows: exposure of 18% of the body area (hands, arms and face) for 5 minutes, two or three times a week, in the spring, summer and autumn seasons, without using sunscreen. These data were collected in the city of Boston, which has a lower ultraviolet radiation index than in the Iberian Peninsula.
So, isn’t sunbathing good for vitamin D and bones?
The amount of necessary solar radiation that we have mentioned is more than acquired just by walking down the street. It is concluded that “actively sunbathing” or exposing oneself to it directly is absolutely unnecessary to synthesize it, and even less so without sun protection.
Do sunscreens make less of it possible?
There is no scientific evidence that the use of sunscreens clearly decreases the synthesis of vitamin D in the skin, so they should not be avoided to hypothetically improve the amount that is manufactured. There are numerous studies that link exposure to ultraviolet radiation and the increase in the incidence of all the most common types of skin cancers.
Without sunshine, how do I get it?
The American Academy of Dermatology and the National Council for Skin Cancer Prevention in the United States recommend that vitamin D be obtained through diet and never through unprotected sun exposure, as the risks associated with it far outweigh the metabolic benefits. In any case, in the Iberian Peninsula, just walking down the street is enough to synthesize the necessary amount, without having to sunbathe.
Is sunbathing good during pregnancy for the fetus to form well?
UV radiation from the sun does not penetrate the skin, so the fetus does not receive any benefit. Vitamin D from the mother is received through the blood and it is not necessary for her to sunbathe to have more of it, as we have seen.
I have osteoporosis and the doctor told me that I have to sunbathe because it is good for the bones. Is that true?
It is not necessary to sunbathe to promote its synthesis if the diet is balanced. Passive sun exposure is enough walking down the street and exposing a minimum of body area. And ideally, it should be with sun protection since there are no contrasted studies that reveal a decrease in vitamin D levels in people who use sunscreens. It is more important to take care of your diet than to expose yourself to the sun.
Is the Sun good for activating defenses?
No. Ultraviolet radiation is, in fact, immunosuppressive: it lowers the skin’s defenses. Precisely for this reason, in addition to causing mutations in the DNA of cells, it is capable of increasing the risk of skin cancer: our own skin defenses fail to eliminate malignant cells in their initial process.
What is true is that vitamin D is necessary for optimal immune system function. However, we have already seen that to have enough it is not necessary to sunbathe.
So, what benefit does the Sun have on the body?
On healthy skin, exclusively psychological and (temporarily) aesthetic. There are people who need to sunbathe because it makes them feel good. This sensation can also be obtained by using sunscreen and avoiding the hours of greatest ultraviolet load (10-17:00h). As for the aesthetic effects, they are not long-lasting: although tanning is flattering, the Sun and UVA rays multiply the speed of skin aging, favoring the appearance of spots, wrinkles, capillaries and skin sagging.
If the sun has no beneficial effect, why do dermatologists recommend it in psoriasis?
Because UV radiation has an immunosuppressive action. It reduces the “excess defences” (inflammation) that occur in some skin diseases such as psoriasis, lichen planus or atopic dermatitis. When suffering from some inflammatory diseases, sun exposure can improve the symptoms. However, it is also known that in patients treated with phototherapy or sunbathing there is an increased risk of skin cancer.
Therefore, can I never sunbathe?
The virtue is in the measure. Exposing yourself to the sun in a protected way, avoiding the hours of greatest radiation and limiting the duration is possible to enjoy the positive psychological and aesthetic effects without causing a disproportionate increase in the risk of skin cancer. To know that the use of sunscreens does not prevent you from tanning, it only slows down the speed of tanning to a small degree and reduces the risk of burning.
REFERENCES
· Woo DK, Eide MJ. Tanning beds, skin cancer, and vitamin D: An examination of the scientific evidence and public health implications. Dermatol Ther. 2010 Jan-Feb; 23(1):61-71.
· Diehl JW, Chiu MW. Effects of ambient sunlight and photoprotection on vitamin D status. Dermatol Ther. 2010 Jan-Feb; 23(1):48-60.
· Sage RJ, Lim HW. Therapeutic Hotline: Recommendations on photoprotection and vitamin D. Dermatol Ther. 2010 Jan-Feb; 23(1):82-5.
· Reichrath J, Reichrath S. Hope and challenge: the importance of ultraviolet (UV) radiation for cutaneous vitamin D synthesis and skin cancer. Scand J Clin Lab Invest Suppl. 2012 Apr;243:112-9.