Sunbathing has been considered harmful to health for at least four decades. The greatest danger comes from ultraviolet (UV) light, which the sun emits in addition to visible radiation. This can increase the risk of skin cancer – the number of diagnoses is increasing – and lead to premature skin aging and the formation of wrinkles. For this reason, most developed countries recommend that sunbathers protect their skin with sunscreen during the heat of the day, especially in the summer months.
The risks of UV radiation are real, but new research suggests it may be time to consider the benefits. According to a recent study published in Health and Place, increased UV exposure appears to significantly reduce the risk of dying from cardiovascular disease or cancer. The risk of dying from melanoma, the deadliest form of skin cancer, was not significantly changed by UV exposure. Although smaller studies had previously suggested health benefits, this is the largest study to show a direct link between UV exposure and longer lifespans.
For their analysis, researchers from the University of Edinburgh used data from over 360,000 people from the UK Biobank, a database. They identified two cohorts that were more likely to be exposed to high levels of UV: those who reported using tanning beds or sunlamps, and those who lived in sunnier locations. To check whether their assumptions about the subjects’ UV exposure were correct, the scientists also examined vitamin D levels in a subset of blood samples. Since vitamin D is synthesized in the skin in the presence of certain forms of UV radiation, it is a reliable indicator of sun exposure.
The researchers then looked at the subjects’ mortality rates, adjusting for other confounding factors such as age, gender, smoking habits and socioeconomic status (in the UK, people who live in sunnier areas tend to be wealthier). They also adjusted for physical activity, as some sunbathers may lead healthier lives outdoors.
Their analysis found that tanning bed users had a 23 percent lower risk of dying from cardiovascular disease and a 14 percent lower risk of dying from cancer than non-users. Similar trends were seen depending on where you lived. For example, someone living in Truro in the south of the UK is exposed on average to about 25 percent more shortwave solar radiation (a measure that includes UV, visible and some infrared light) per year than someone living in the much further north cities of Glasgow or Edinburgh. The team concluded that this translates to a 19 percent lower risk of dying from cardiovascular disease and a 12 percent lower risk of dying from cancer. In other words, tanning bed users lived an average of 48 days longer than non-users over the 15 years they were studied. The equivalent figure for people living in sunnier places was 26 days.
According to Richard Weller, co-leader of the study, the focus of most UV radiation recommendations to date has been clearly on preventing melanoma. But “many more people die from other cancers and diseases,” he says. “We need to think about how UV radiation can help them prevent disease.”
The exact mechanism by which UV light can prolong life is unknown. For their part, the authors believe part of the explanation may lie in vitamin D’s ability to boost the immune system and improve bone health. They also point to nitric oxide, a powerful blood vessel dilator that may reduce the risk of cardiovascular disease. A 2014 study published in the Journal of Investigative Dermatology showed that nitric oxide is released in skin cells exposed to moderate UV radiation, and sunlight helps transport it to the bloodstream, where it may have health-promoting effects. The researchers hope that future studies will further elucidate the causal chain.
There are other questions that need to be answered. First, Dr Weller’s team could only analyse data from people living in the UK: attitudes to the risks and benefits of sunbathing might differ elsewhere. The structure of the data also meant they could not take into account sunscreen use.
Perhaps most importantly, they only studied participants who were predominantly white European ancestry to ensure that the response to UV radiation was uniform. “We know that skin color affects the body’s response to UV light, but we don’t yet know how,” says Dr. Weller. Because people with darker skin are most at risk of vitamin D deficiency, more research is needed on how UV radiation affects this population, says Frank de Gruijl, professor emeritus of dermatology at Leiden University Medical Center. “We need to look at the biology.”
The new research could prompt scientists and health experts to take a closer look at the benefits of UV exposure versus its risks, and perhaps provide more nuanced advice in the future about how different groups of people can best protect themselves from the sun. But experts agree that the study is not a license to forgo sunscreen for now.
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