This study showed that ultraviolet radiation (UVR) can cause damage to the DNA in skin cells and increase the production of vitamin D. This can happen at levels below the level that would cause sunburn, in all skin types.
Our skin is made up of several different layers. The research team measured the levels of DNA damage in the top layer. This is called epidermis. It included the lower layer of the epidermis called the basal epidermal layer. Researchers think this is the layer where most skin cancers start.
The research team measured the change in production of vitamin D in the skin. They did this my measuring the amount of something called 25-hydroxyvitamin D in the blood. They measured this in 39 people:
- 19 had light or medium skin (type 1, 2 or 3)
- 20 had dark or very dark skin (type 4, 5 or 6)
They measured the change in vitamin D production a week after each UVR exposure. They found that it increased for all levels of exposure, in all skin types. But it increased more with higher levels of UVR.
Vitamin D production increased for people with light skin and dark skin.
The research team measured the amount of DNA damage in 26 people:
- 17 had light or medium skin (type 1, 2 or 3)
- 9 had dark or very dark skin (type 4, 5 or 6)
They measured the change in DNA damage 15 minutes and 48 hours after each UVR exposure. They found that there was some DNA damage in cells in the top layer of skin 15 minutes after exposure. This happened at all levels of exposure and for all skin types. But higher doses of UVR caused more damage.
They then looked at the lower layer of skin, where cancer often starts. They found there was only DNA damage in people with lighter skin. There was hardly any DNA damage in the lower levels of darker skin. This could help explain why people with darker skin have a lower risk of skin cancer.
When they looked at the DNA damage 48 hours after each exposure, they found that most of the damage had been repaired. It was similar to the level of damage before UVR exposure. This happened for all levels of UVR exposure and all skin types. But the research team think that damage to the DNA in skin cells could lead to future problems, even if it is ultimately repaired.
The research team concluded that even very low levels of ultraviolet radiation can increase vitamin D production and cause DNA damage, in all skin types. The level is well below the usual level that would cause sunburn (the minimal erythemal dose, or MED).
For light skin they found that DNA damage can happen in the upper and lower layers. But for dark skin it was only in the upper layers. This helps to explain the higher risk of skin cancer for people with light skin.
The research team hope this information will help people who decide what advice to give the public about sun exposure.
Where this information came from
We have based this summary on information from the research team. The information they sent us has been reviewed by independent specialists (peer reviewed
) and published in a medical journal. The figures we quote above were provided by the trial team who did the research. We have not analysed the data ourselves.