Since the use of sunscreens has been on the rise, they have gained many advocates as well as many opponents. Opponents of sunscreens claim that they block the synthesis of vitamin D, which is essential for our health. There are also extreme opponents who claim that using sunscreens is more harmful than unprotected sun exposure. However, is it true that sunscreens block vitamin D synthesis?
Basic information on vitamin D
Vitamin D acts as a hormone in the body and is synthetized by UV light. Vitamin D comes in two forms (D₂, D₃). Vitamin D₂ is obtained from plant nutrition and oral supplements. Vitamin D₃ is mainly obtained by exposing the skin to ultraviolet B (UVB) radiation in sunlight and consuming foods such as oily fish. Vitamin D₂ and D₃ are metabolised in the liver and kidney to 1,25-dihydroxyvitamin D or calcitriol, which is a biologically active form. Calcitriol plays an important role in regulating the metabolism of calcium, phosphate for maintaining metabolic functions and for skeletal health.
How can one get vitamin D?
Vitamin D is also found in mushrooms, wheat germ oil, egg yolk, liver and fish oil. Vitamin D content in most foods ranges from 50 to 200 units per serving. Therefore, food cannot provide enough vitamin D, which is why most people synthetize it after sun exposure. Sun-induced vitamin D synthesis is strongly influenced by season, time of day, latitude, altitude, air pollution, skin pigmentation, use of sunscreens, passage through glass and plastic, and age.
Interesting fact: Even when older people are regularly exposed to sunlight, they produce 75% less vitamin D3 than young people.
Inadequate vitamin D intake can lead to postmenopausal osteoporosis and reduced bone density. Low vitamin D intake is also associated with heart and vascular diseases, depression, dementia and other conditions.
How is vitamin D synthesized after sun exposure?
Vitamin D3 can be produced in the skin when exposed to ultraviolet radiation B (UVB), so it is possible to increase vitamin D3 levels by exposure to UVB rays. During exposure to sunlight, radiation with a wavelength of 290–315 nm penetrates the skin. Most of this UVB radiation is absorbed in the epidermis, so when exposed to sunlight, most of the vitamin D3 is produced in the skin, in the living cells of the epidermis.
A quick recap on UV radiation
As we already know, exposure to UV radiation is not safe. Namely, we divide the UV spectrum into ozone-retained UVC rays, UVB rays that cause sunburns, UVA rays that cause photoaging. Unnecessarily prolonged exposure to UV light without protection can lead to skin cancer. For a reason, sunscreens have been developed to protect us from the harmful effects of UV radiation. Sun creams are designed to absorb and partially repel UVB radiation.
If sunscreen blocks UVB rays does it block vitamin D synthesis as well?
Well, here we are. Where scientists from different disciplines are arguing with each other. Last time, I heard from a colleague that one dermatologist claimed that reduced vitamin D synthesis from sunscreens is more harmful than unprotected sun exposure. To put it mildly, I was almost hit by a stroke, but let’s go down the line. Sunscreen with sun protection factor (SPF) 30 absorbs approximately 96% of UVB radiation. So, by adding 2 + 2, topical application of sunscreen with SPF 30 reduces the skin’s ability to produce vitamin D3 by the same amount, ie 96%.
In principle, we calculated that only 4% of UVB radiation can access our skin with SPF 30, which is a very low chance for vitamin D synthesis, right? But this is where you need to ask yourself how much sunscreen you really apply to your skin. In order to achieve the protection stated on the packaging – so in our case SPF 30 we need to apply 2mg / cm2 of skin. For the whole face, this means two full fingers of the cream.
A short calculation to back up my claims
The average surface area of all skin in an adult is 1.5-2.0 m². So if we need to apply 2mg / cm² the calculation is as follows.
The result is 32 g per coat. Therefore, 1/3 of the entire 100 ml tube of sunscreen should be used to properly protect the entire body. Of course, we did not take into account that the sunscreen should be reapplied every 2 hours.
Let’s be real, we apply such a small amount of sunscreen to the body that the question is if we have an SPF protection factor of 5. So with SPF 5, we are about 70% protected against UVB radiation. This may sound like a lot, but this time it can pass as much as 30% of UVB radiation to the skin! Not to mention some body parts that are not usually protected at all. Or maybe we are in the shade and don’t put sunscreen on because the UVB rays can’t reach us. All of these unprotected parts allow 100% passage of UVB radiation and thus synthesis of Vitamin D, but also increased chances of skin cancer.
UVA protection is beneficial for Vitamin D
A number of studies investigating the influence of sunscreen on vitamin D synthesis have found that the use of sunscreen is likely to have minimal impact on vitamin D. UVA rays have no effect on vitamin D synthesis, although one in vitro study showed that UVA2 (315–340 nm) can cause vitamin D to break down, in which case protection against UVA may be beneficial for vitamin D production.
Controlled field studies with true sun exposure are the best way to determine the effect of sunscreen on vitamin D synthesis. The results of such studies report that no change in serum 25 (OH) D3 vitamin concentration occurs despite the use of sunscreen.
In fact, most studies published to date have shown no association between the use of sunscreens and vitamin D deficiency, nor with regular use of SPF> 15. In general, other protective methods (eg, shading, wearing protective clothing and long sleeves) ) affect vitamin D status more than using sunscreens.
UV radiation is more dangerous than sunscreens
Daily skin protection is recommended for all skin phototypes. This includes staying in the shade, wearing headgear and clothing, wearing sunglasses, and applying broad-spectrum sunscreen. These strategies will help prevent sunburn and skin cancer. The use of sunscreen for daily sun protection does not compromise the synthesis of skin vitamin D synthesis, even when the sunscreen is used in the predicted amounts (2mg / cm2). Increasing UVA-PF in sunscreens, however, even improves vitamin D3 production.
In case of reduced vitamin D level, this should be replaced. Oral supplementation is easy and does not pose significant risks. The risk-benefit calculation shows that, instead of sunbathing, it is better to take nutritional supplements with this vitamin to increase vitamin D3 levels.