Are we addicted to sunbathing?

Skin cancer rates are rising as people ignore warnings about overexposure to the Sun. Researchers say it is the opiate-like feel-good factor that drives us back for more. Suzanne Shubart reports.

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Exposure to ultraviolet (UV) light appears to increase endorphin levels in mice and could explain why some people continue to sunbathe despite the risks.

While the connection between sunbathing and cancer has been known for decades, many of us continue to bask in the Sun with disastrous results. Why do we do it? Could we be ultraviolet addicts?

A study published in Cell on 19 June suggests many of us may well be. The research reveals that extended exposure to UV radiation causes the release of the happiness hormones called endorphins. These act through the same pathway as heroin and morphine leading to physical dependence, tolerance and addiction-like behaviour in mice.

For years senior study author David Fisher of Harvard Medical School had wondered whether just such a mechanism could also be drawing us to the Sun regardless of the risks.

In Australia, skin cancers account for around 80% of all newly diagnosed cancers. Skin cancer is the most common form of cancer in the United States where incidence of squamous cell carcinoma, the second most common cancer of the skin, has doubled in the past 30 years and melanoma, the most common cancer in young adults, has risen about 2% per year in the past decade. Fisher began to suspect that there could be something driving the urge to sunbake, “…beyond the simple decision ‘Oh, let’s go outside and feel good’.”

Skin cancers are the the most common form of the disease and most are caused by over-exposure to ultraviolet light. – iStock

To test whether the opioid pathway – the one activated by drugs like morphine – could play a role in sun-seeking behaviour, Fisher and his team exposed mice with shaved backs to ultraviolet (UV) light five days a week for six weeks and found that endorphin levels in the bloodstream increased within a week. Afterwards, these mice developed a tolerance to morphine (they needed higher doses to relieve pain than non-UV-exposed mice), adding to the evidence that UV-induced endorphins had stimulated the opioid pathway. Further, when the UV-exposed mice were given a drug that blocked the effects of morphine, they got the shakes and their teeth chattered – typical withdrawal symptoms.

“Lying in the sun on holidays and absorbing the sun’s rays makes you feel better and now we know why,” says Dan Lubman, Professor of Addiction Studies at Monash University. He stresses, though, that “this does not mean all people who sunbathe will lose control over their behaviour and find it almost impossible to stop”. Pascale Guitera, a dermatologist at the Melanoma Institute Australia and Director of the Sydney Melanoma Diagnostic Centre, however, describes “some patients who are really quite marred by the sun – they look ugly and they know they look ugly, but they still want to have more. They tell you that they love the sun.” She said she was not at all surprised by Fisher’s findings.

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