A study measuring the risks and benefits of exposure to sunlight

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Cancer type:

Non melanoma skin cancer
Skin cancer





This study looked at the effects of exposure to sunlight in healthy volunteers who had not been diagnosed with skin cancer. It was supported by Cancer Research UK.

More about this trial

Ultraviolet radiation (UVR) from sunlight can cause damage to skin cells. This can lead to both melanoma skin cancer and non melanoma skin cancer. But we do need some sunlight so that our bodies can make vitamin D.
Researchers wanted to find out more about the good and bad effects of ultraviolet radiation. To do this, they measured markers of vitamin D production and damage to the genetic material (DNA) in skin cells.
This study recruited people with different skin types, ranging from very light (type 1) to very dark (type 6). The research team worked out the level of UVR that would cause sunburn in each person taking part. This is called the minimal erythemal dose (MED). They used the MED to calculate the levels of ultra violet radiation to use in the study. So everyone taking part was exposed to different, personalised levels of UVR.
The people taking part had about one third (35%) of their body exposed to UVR 4 times, with a month between each exposure.
The 4 levels were:
  • 20% of the level which would cause their skin to burn
  • 40% of the level which would cause their skin to burn
  • 60% of the level which would cause their skin to burn
  • 80% of the level which would cause their skin to burn
The aims of this study were to see:
  • what level of UVR exposure causes damage to the DNA in skin cells
  • what level of UVR exposure increases the production of vitamin D
  • if there are differences between different skin types

Summary of results

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.
Skin cells
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.
Vitamin D
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.
DNA damage
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 Open a glossary item) 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.

Recruitment start:

Recruitment end:

How to join a clinical trial

Please note: In order to join a trial you will need to discuss it with your doctor, unless otherwise specified.

Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Chief Investigator

Professor Lesley Rhodes

Supported by

Cancer Research UK
NIHR Clinical Research Network: Cancer
NIHR Manchester Biomedical Research Centre
Salford Royal NHS Foundation Trust
University of Manchester

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Last review date

CRUK internal database number:


Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Around 1 in 5 people take part in clinical trials

3 phases of trials

Around 1 in 5 people diagnosed with cancer in the UK take part in a clinical trial.

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