The Economist: Exposure to the Sun’s UV radiation may be good for you

Basking in the sun has been considered a health hazard for at least four decades.

The main risk comes from ultraviolet (UV) light, which the Sun emits alongside visible radiation. This can increase the chances of skin cancer — the number of diagnoses of which are rising — as well as bringing on premature ageing and leading to wrinkles.

As a result, most developed countries recommend sunbathers protect their skin in the heat of the day with sunscreen, especially in the summer months.

The risks UV poses are real, but new research suggests it may be time to consider the benefits.

According to a study published recently in Health and Place, increased UV exposure appears to make people significantly less likely to die from cardiovascular disease as well as cancer.

The risk of dying from melanoma skin cancer, the most deadly form of skin cancer, did not meaningfully change with UV exposure.

Although smaller-scale studies have previously nodded to such health benefits, this is the largest study to show a direct correlation between UV exposure and longer lifespans.

To conduct their analysis, the researchers from the University of Edinburgh used data from over 360,000 people in the UK Biobank, a database. They identified two cohorts more likely to have high UV exposure: those who claimed to use sunbeds or sunlamps; and those living in sunnier locations.

To check that their assumptions about the subjects’ UV exposure were correct, the scientists also looked at vitamin D levels in a subset of blood samples. As vitamin D is synthesised in the skin in the presence of certain forms of UV radiation, it is a reliable indicator of sun exposure.

The researchers then examined the subjects’ death rates while correcting for other confounding factors, including age, gender, smoking and socioeconomic status (in Britain, those who live in sunnier climes are typically wealthier). They also corrected for exercise, as some sun-seekers might lead healthier outdoor lives.

Their analysis showed that sunbed users were 23 per cent less likely to die of cardiovascular disease, and 14 per cent less likely to die of cancer, than non-users.

Similar trends held depending on where people lived. Someone living in Truro, for example, would on average experience about 25 per cent more solar shortwave radiation (a measure that includes UV, visible and some infrared light) in a year than someone living in Glasgow or Edinburgh.

In the team’s analysis, this translated to a 19 per cent lower risk of dying from cardiovascular disease and 12 per cent lower risk of dying from cancer. Sunbed users, in other words, lived an average of 48 days longer than non-users over the 15 years during which they were studied. The corresponding figure for those living in sunnier locations was 26 days.

According to Richard Weller, who co-led the study, most UV exposure guidance has thus far been firmly focused on preventing melanoma skin cancer.

But, he says, “many times more people die from other cancers and diseases. We have to think about how UV radiation could help them avoid illness.”

The exact mechanism whereby UV light might lengthen lives is not yet known. The authors, for their part, believe that part of the explanation may be vitamin D’s ability to boost the immune system and improve bone health.

They also point to nitric oxide, a potent blood-vessel widener, capable of lowering blood pressure and reducing the risk of cardiovascular disease.

Research published in the Journal of Investigative Dermatology in 2014 showed that nitric oxide is released in skin cells that have moderate exposure to some UV radiation, and sunlight helps move it into the circulatory system where it could have health-boosting effects.

The researchers hope that future studies might further clarify the causal chain.

There are other questions too that need answering. For one thing, the authors of this latest paper were only able to analyse data from individuals living in Britain: there could be different attitudes to the risks and benefits of sun exposure in other places. Owing to the structure of the data, they also could not control for sun-cream use.

Most important, perhaps, they restricted their analysis to participants of mostly white European ancestry, to ensure the response to UV was consistent.

“We know that skin colour affects your body’s response to UV light and we don’t yet know how, because we have to do more studies,” says Dr Weller.

As people with darker skin are most at risk from vitamin D deficiency, more research on the effects of UV exposure on this population is of “great importance”, says Frank de Gruijl, an emeritus professor of dermatology at Leiden University Medical Centre.

“We need to dig into the biology and identify the underlying mechanisms.”

Some tweaks to established guidance are already being made. In February the Australian government established new sun-safety guidelines, endorsed by health bodies including Cancer Council Australia and the Australasian College of Dermatologists, to reflect the needs of Australians with darker skin.

Whereas pale-skinned Australians are still advised to protect themselves from the sun at all times, those with dark skin only need protection if they are in the sun for long periods of time.

The new research may prompt scientists and health experts elsewhere to look deeper into the benefits of UV exposure versus its risks and, perhaps in the future, make available more nuanced advice about how different groups of people can best stay safe in the sun. But for now, experts agree, the study is not a licence to stop wearing sun cream.