Here I’m gonna be talking about sun exposure and vitamin D and I’m gonna be answering the million dollar question: does sunscreen block vitamin V? In other words, does wearing sunscreen cause low vitamin D?
Are we still able to get good vitamin D while we’re wearing sunscreen?
We’re exposed to ultraviolet radiation from the Sun and a part of that ultraviolet radiation can kick off the beginnings of vitamin D synthesis, starting in our skin.
Vitamin D is really important for our bone health, for our musculoskeletal system, it also seems to have a major role in immune function. Low vitamin D levels have been associated with cancers and a variety of chronic metabolic diseases, chronic health problems.
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Before I get into the interaction between ultraviolet radiation and the skin in terms of kicking off vitamin D synthesis, you have to understand what ultraviolet radiation is coming from the sun and what that means.
Ultraviolet radiation is actually three different parts: UVC, UVB and UVA.
Of those three parts, UVC is blocked out completely by ozone, so it never really touches our skin.
UVB is attenuated by the ozone layer, meaning some of it gets through.
UVA is free to come on down
UVB and UVA are the two parts that actually impact our skin. UVB is the part that initiates vitamin D synthesis in the skin. UVB is also the part that burns our skin and causes DNA mutations.
UVA however which also touches our skin has no impact on kicking off vitamin D synthesis. It doesn’t do anything for initiating vitamin D synthesis.
UVA is a very damaging part of ultraviolet radiation because it penetrates the skin very deeply. It reaches the basal cells of the epidermis (the top layer of the skin) and generates DNA mutations in the stem cells.
It also suppresses the immune system, impairing tumor surveillance and it destroys collagen by activating matrix metalloproteinases, ultimately weakening the skin and the skin’s ability to protect us from the outside world and creating a lot of damage that ultimately leads to skin cancers.
Because the ozone layer attenuates UVB but doesn’t UVA, the actual ultraviolet radiation that ends up reaching your skin, 95% of it is UVA and less than five percent of it is UVB.
So it is that small fraction, that less than five percent, that is actually meaningful when it comes to vitamin D synthesis in the skin.
How Vitamin D is Made in The Skin
Within our skin we have a variety of things called chromophores that absorb ultraviolet radiation.
7-Dehydrocholesterol is a chromophore in the skin that absorbs UVB and generates something called pre-vitamin D3.
That pre-vitamin D3 is immediately converted to vitamin D3. However you need to understand that exposure to heat and UVA can cause degradation of both pre-vitamin D3 and vitamin D3.
Vitamin D3 from the skin, it’s not active, it’s not helping you at that point. It has to enter the circulation by binding to something called vitamin D binding protein.
It goes to the liver, it receives a hydroxyl group and then it goes to the kidney and receives another hydroxyl group and at that point it is active, it’s something called calcitriol, which is a hormone and that the end goal is.
While D3 enters circulation and goes to the liver and the kidneys, there are other tissues that have some of the machinery that can convert vitamin D3 to its active state. But the majority of it is going to go through this pathway. In other words, there are some of these enzymes in other tissues, including the skin.
Why Sun is Not a Good Way to Get Vitamin D?
Why is it not as simple as just going out and sunbathing to get your vitamin D?
Remember the part of ultraviolet radiation from the sun that can do vitamin D kick off in the skin is UVB, not UVA. The intensity of UVB or the irradiance of UVB varies a lot.
The sun’s height determines the path length of ultraviolet radiation through stratospheric ozone. The ozone attenuates some of UVB coming through.
Beyond the influence of weather, time of day, position of the sun in the sky, the other piece has to do with you. People vary a lot in terms of their ability to kick off that vitamin D synthesis in the skin.
It varies a lot with body surface area exposed as well as your genetics. Some people’s genetics is such that it’s just more efficient, whereas other people are not.
It also varies with your skin tone. People who have a deeper skin tone have a different constitution of the pigment that absorbs a lot of UV, so their skin is absorbing and blocking out a lot of UV, making it so that the dehydrocholesterol isn’t able to kick off the vitamin D synthesis.
It also varies with your age. As we get older, our skin doesn’t contain as much of this enzymatic machinery necessary to begin vitamin D synthesis.
When you’re talking about going outside to get vitamin D, you have to understand the fact that there is not an amount of sun exposure that you can receive that’s going to exclusively be those UVB rays that activate vitamin D synthesis. You’re also going to get a mega dose of UVA, the rays that penetrate to the stem cells in your skin, generating DNA mutations that ultimately lead to skin cancer.
They suppress your immune system, impairing tumor surveillance, they also destroy your collagen, weaken skin barrier function, make your skin more vulnerable to environmental stressors, age the skin and contribute to hyperpigmentation. It also interacts with metabolites and medications you might be taking to cause different skin rashes
So there is a lot of damage from those UVA rays that accompany the smaller fraction of UVB that can actually do the vitamin D synthesis thing.
Those UVB rays are also what is responsible for burning the skin and generating DNA damage as well.
So you can see the problem here with chasing sun exposure as a means of vitamin D synthesis.
There are safer ways to get vitamin D through supplements and through your diet.
Low Vitamin D and Health Problems
While we know how important vitamin D is for bone health, we don’t really have the full story on its association with things like cancer and other chronic diseases.
While it keeps showing up as being lower in people with these issues, the studies show that supplementing and raising the vitamin D doesn’t impact mortality or disease outcome whatsoever.
So whether or not low vitamin D is responsible or merely a bystander, it is hard to say.
For example, a lot of people with autoimmune diseases have high levels of inflammation as part of their disease process. There is some evidence that vitamin D is a negative acute phase reactant. What the heck is that?
When there’s inflammation in the body, certain lab markers go up. You may be familiar with the c-reactive protein or CRP. That is high inflammatory states.
But you can have negative acute phase reactants that go down in the setting of inflammation and vitamin D is thought to possibly be a negative acute phase reactant. So in people who have a lot of inflammation, like people with autoimmune diseases, then it makes sense that they might have a low vitamin D.
Also people who are obese tend to have a low vitamin D level, probably because vitamin D is fat soluble, so they may be not mobilizing it properly. And being obese is an inflammatory state, releases a lot of inflammatory mediators that caused a lot of chronic health problems.
Logic would follow that with that level of inflammation, you would have lower vitamin D. It’s unlikely due to the fact that obese people or people with autoimmune diseases are not sunbathing enough.
Wearing Sunscreen and Vitamin D Levels
What about sunscreen?
I’m always advocating to wear sunscreen daily, regardless of what you’re doing and reapply it consistently.
It’s important to protect your skin from a sunburn and those UVB rays, but the more pressing issue, especially on a day-to-day basis, is protecting your skin from UVA. Those are the rays that are not blocked out by ozone. Those are the rays that get down to the basal layer of your skin and the stem cells and cause DNA mutations, cause free radical damage, destroy the collagen in the skin.
I could go on and on about all the downsides of exposing your skin to UVA. It’s very dangerous, it even comes through window glass, which is a reason to wear sunscreen on a daily basis.
What are sunscreens?
Sunscreens are topical formulations that contain ingredients that attenuate ultraviolet radiation.
They attenuate UVB rays as well as the rays that are responsible for kicking off vitamin D synthesis in the skin.
There is this overarching concern that wearing sunscreen is going to impair your skin’s ability to generate good vitamin D.
When you pick up a sunscreen, probably the first thing that’s going to jump out at you is the SPF. It is a quantitative index of protection, specifically protection against erythema or redness.
It’s measured after one exposure using something called solar simulated radiation. It’s a source of radiation that is meant to simulate what comes from the sun.
The final SPF is actually a ratio of the solar simulated radiation dose needed to barely begin to generate the first signs of redness, which is skin damage. The ratio of that on skin with sunscreen versus skin without sunscreen.
Because the SPF is looking at redness and burning, it is basically telling you how well the product is going to protect you against the UVB rays.
The other factor of a sunscreen is UVA protection. Sunscreens are required to protect you from UVA rays.
Sunscreen does not completely block out those UVB rays. UVB rays are the ones that kick off vitamin D synthesis, but also cause redness.
A given sunscreen applied at the recommended amount of two milligrams per centimeter square, which is pretty heavy, is going to allow penetration of the inverse of the SPF. A penetration of a redness relevant dose of UV.
If you go out sunbathing and expose yourself to 30 standard erythematous doses of ultraviolet radiation from the sun, what that’s going to translate into is if you’ve got an SPF of 20 at maximum recommended use of 2 milligrams per centimeter square, that is basically 1 over 30 times, which is 1.5 standard erythematous dose.
So you’re still getting an exposure to rays that can cause redness and that translates again into those UVB rays. Remember, UVB burns and kicks off vitamin D synthesis in the skin.
Using sunscreen in maximum use condition should still allow some of those rays to penetrate into the skin.
Benefits to Applying Sunscreen
There are numerous benefits to applying sunscreen.
It’s been shown to reduce the appearance of photo aging, as well as reduce the rates of melanoma and squamous cell carcinoma.
It also has been shown to reduce biologic endpoints associated with ultraviolet radiation, namely a burn, DNA damage, immunosuppression, destruction of collagen, all these things.
Wearing sunscreen can attenuate those tremendously long term, protecting the health of your skin and reducing your risk of skin cancer.
Does Sunscreen Prevent Vitamin D Synthesis?
Since we’re wearing sunscreen and blocking out those UVB rays, does that actually translate into lowering your vitamin D?
Studies show that when applied under maximal use conditions on a vacation, sunscreens do not lower vitamin D levels.
There is also a study in the Canary islands during a week of high UV exposure.
This is probably one of the best studies that we have looking at this, because it’s actual sun exposure on actual holiday. They had a group of people who were just allowed to apply sunscreen at discretion and then they had an intervention group where they had them apply sunscreen at the recommended amount two milligrams per centimeter square.
At the end of the study, it showed that sunscreen did in fact inhibit the formation of redness, but still enabled considerable vitamin D synthesis, despite using the maximum recommended amount.
They also looked at two different types of sunscreen.
One with high UVA protection and one with low UVA protection.
The higher the UVA protection of the sunscreen, the better vitamin D synthesis!
It’s been suggested that UVA, which is the majority of the ultraviolet radiation that comes from the Sun, actually causes photo degradation of vitamin D in the skin.
So having a sunscreen on that blocks out more UVA is likely to come with a commensurate ability to allow a little bit more of the UVB rays necessary to activate vitamin D synthesis, while blocking out those vitamin D degrading UVA rays.
That’s actually a plug for sunscreen in favor of vitamin D, rather than as an opponent to vitamin D.
There is no amount of sun exposure that you can receive that will raise your vitamin D without exposing you to whopping doses of these carcinogenic UVA rays.
It’s like putting vitamin D in a cigarette.
If suddenly big tobacco started putting vitamin D in cigarettes, we’re not all going to start smoking cigarettes to raise our vitamin D.
Same thing with ultraviolet radiation. It is a confirmed carcinogen.
Why are you going to expose yourself to megadoses of a confirmed carcinogen in the hopes of raising your vitamin D, which you can get much more safely from your diet and from supplements?
Of course spending time outdoors is beneficial to your overall health.
Fresh air likely is good for you.
There are studies showing that people who spend time outdoors have better immune function.
Whether or not that has to do with UVB, kicking off vitamin D synthesis, it seems unlikely, given everything that I’ve just told you.
It’s probably because people who spend more time outdoors have better stress responses or maybe people who spend more time outdoors doing things like hiking or exercising, take better care of themselves than people who don’t do those things.
There are so many other things you have to take into account before just running outside and sunbathing. That really puts your skin at a lot of risk for DNA damage and destruction.
In summary, there is no amount of sun exposure that you can get that will safely raise your vitamin D levels without exposing you to DNA damage, collagen destruction, all sorts of damage to your skin, age your skin, weaken the skin barrier.
Vitamin D should be obtained safely from your diet and if needed, supplements.
Sunscreen application under maximal use conditions in the real world, with real sun exposure, does not block vitamin D synthesis.
In fact sunscreens that offer a high level of UVA protection can actually make your skin a better vitamin D synthesizing machine.
There’s no reason to fear that sunscreens will cause you vitamin D deficiency!
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vitamin D synthesis without sunburn. Br J Dermatol 2019; https://doi.org/10.1111/bjd.17888
- Neale RE, Khan SR, Lucas RM et al. The effect of sunscreen on vitamin D: a review. Br J Dermatol 2019; https://doi.org/10