Professor Lesley Rhodes

Research sheds new light on risks and benefits of sun exposure

For the first time researchers have shown the differing relationship between benefit and risk of sunlight (UVR) exposure for people of different skin types, with findings published in the Journal of Investigative Dermatology.

It’s well known that exposure to sunlight carries positive and negative effects, namely increasing the risk of skin cancer with more than 150, 000 new cases diagnosed in the UK each year. But, what isn’t as well known is how the risk and benefit relationship differs between different the skin colours, from the lightest to the darkest.

Researchers from the NIHR Manchester Biomedical Research Centre set out to find out whether different skin tones can gain vitamin D from sunlight while avoiding damage to DNA in the outer, epidermal layer of skin.

Led by Professor Lesley Rhodes, BRC Programme Lead for Photodermatoses and Honorary Consultant at Salford Royal, researchers performed an experimental dose-response study related to personal sunburn sensitivity. Study participants with skin types ranging from very light to very dark were given sub-sunburn UVR exposures, with researchers taking samples to make a direct comparison of relationships for vitamin D and DNA damage.

The team found that everybody gained the same amount of vitamin D, which shows sun exposure can be beneficial to everybody, regardless of skin colour.

While the total amount of epidermal DNA damage was also equivalent in all subjects, when given a UVR dose related to their sunburn sensitivity, there is a gradient of DNA damage across the epidermis from the surface to the basal cells, the steepness of which correlates with level of skin darkness. Thus, as skin melanisation increases, there is progressive protection against basal cell DNA damage, the critical cell layer in the skin which is at the highest risk of transforming to skin cancer.

However when looking at the lightest skin types, DNA damage occurred evenly over the epidermal depth.  Even exquisitely low UVR doses cause basal cell damage meaning they cannot gain vitamin D without this damage taking place.

These new findings show that there is an advantageous benefit: risk relationship to sunlight exposure in darker skin types, who can be encouraged to use sub-sunburn sunlight exposures to gain vitamin D. This is not the case in lighter skin types, as extremely low UVR exposures produce DNA damage in basal cells, where carcinogenic risk is greatest, offering an explanation for their high skin cancer incidence, and challenging guidance on gaining vitamin D ‘safely’ through brief sun-exposures below their visible sunburn level.

Professor Rhodes explained: “The relationship between vitamin D synthesis and DNA damage and how these are influenced by skin type was previously poorly understood. Our study informs those forming public health messages on sun-exposure in relation to sunburn, vitamin D acquisition and skin cancer risk. This research shows the importance of personalised approaches to sun exposure and health, based on an individual’s skin tone.”

This research was funded by Cancer Research UK Biomarkers and Imaging Discovery and Development scheme (Ref: C30431/A13128) and supported by the NIHR Manchester Biomedical Research Centre.