Dermatologist Debriefs

Vitamin D, Windows, and The Sun: A Dermatologist's Perspective

• Stefanie Williams

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Wondering if that sunny spot by your office window is giving you all the vitamin D you need? Dr. Stefanie tackles this common misconception head-on with scientific clarity.

The truth might surprise you: despite feeling the sun's warmth through glass, your body isn't getting the specific ultraviolet rays needed for vitamin D production. This episode breaks down the crucial difference between UVA rays (which can penetrate glass and age your skin) and UVB rays (which are blocked by windows but essential for vitamin D synthesis).

Speaker 1:

Dermatologist debriefs. Join no-nonsense dermatologist Dr Stephanie Williams as she debunks myths and shares her professional insights, separating facts from fiction, in just a few minutes.

Speaker 2:

Hello, this is Dr Stephanie. I was just asked by one of my patients whether they really have to take their vitamin D supplement now that it's starting to get sunnier outside. This patient has an office job and spends most of her day inside, but she argued that her office is very bright and she sits right by the window where there is a lot of sun coming in. So today's question is can our skin produce enough vitamin D when sitting behind a window on a sunny day? And the answer to that is no, and this is because the action spectrum of vitamin D production lies in the UVB range. Production lies in the UVB range, and UVB does not penetrate glass windows. So if we look at this in a little bit more detail, we all know that vitamin D production requires ultraviolet rays from sunlight, and vitamin D production is most efficient when the sun is at its highest point in the sky, which is around midday, and, of course, the larger the area of skin exposed, the more vitamin D is produced. However, it's UVB, specifically from the ultraviolet range, that is required for vitamin D production.

Speaker 2:

For vitamin D production, uvb includes wavelengths from 280 to 320 nanometers, which is compared to UVA, the higher energy portion of the sunlight, which can cause our skin to burn. However, although the UVB range compared to UVA has higher energy, uvb is relatively easily blocked or at least reduced, let's say, for example, by clouds or by clothing or even normal window glass. So this is in contrast to UVA, which has longer wavelengths, namely 320 to 400 nanometers. But UVA can penetrate not only much deeper into the skin but also has a much better ability to penetrate things like clouds and window glass, and that's why, when you're sitting inside behind a window, you will generally not burn. But your skin can still age prematurely and you can see that, for example, in professionals who drive, for example, lorry drivers or taxi drivers, taxi drivers and if you compare their hands and forearms, you can see that generally the side that is closer to the window is looking more prematurely aged than the other side.

Speaker 2:

So, to cut a long story short, uva can window glass, but it is not useful for our skin with regards to vitamin D production. So this action spectrum lies firmly in the UVB range and that does not penetrate window glass. And, on that note, if we're wearing sunscreen, which also greatly reduces the UVB getting into the skin, that of course then also limits our vitamin D production in the skin. So what are the alternative sources? That's, of course, besides sunlight supplements, which I highly recommend taking. Some foods also contain a certain degree of vitamin d, like fatty fish or egg yolks, but it's not generally enough. So either you expose your skin directly to the sunlight outdoors, which obviously comes with its downsides, or you start taking a supplement. I hope this makes sense and I will speak to you very soon.