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New study finds UV light may be physically addictive -

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TANYA NOLAN: New research by scientists in the United States suggests that the ultra violet light from the sun may be physically addictive.

Researchers from Massachusetts General Hospital conducted experiments on mice which showed them becoming addicted to UV light.

It also showed the lab animals displaying physical signs of withdrawal when they were denied access to UV rays.

Experts say the research has ramifications for how the sun smart message is delivered in Australia, which has the highest incidence of skin cancer in the world.

Rachel Carbonell reports.

RACHEL CARBONELL: Chairman of the Department of Dermatology at Massachusetts General Hospital, Dr David Fisher, led the study, which has been published in the journal Cell today.

The research systematically exposed mice to ultra violet radiation and observed the results.

DAVID FISHER: We were able to identify behavioural consequences that looked very much like addiction that were behavioural changes that indicated an endogenous opiate signalling going on that the mice would become gradually numb to sensory input, just like morphine would have done. Maybe not quite as potently as morphine, but a very similar opiate-like effect.

We could see that there was a dependency to UV radiation in which abrupt blockage of the opiate pathway using a drug, using the same drug you would give a heroin overdose patient in the emergency room, such an opiate blocking drug in a mouse that has been receiving daily UV radiation actually produced withdrawal symptoms - shaking and chattering and jumping. Types of symptoms that you would similarly see if the mouse had been addicted to an opiate drug like morphine.

RACHEL CARBONELL: Do you think there's a chance that that particular mechanism that you've identified in your study has an evolutionary function in the sense that we've come to see sun exposure as a very bad thing, but of course the sun has health benefits as well.

DAVID FISHER: Yes, we suspect it does originate in a manner that was evolutionary selected but exactly what that mechanism is I can speculate and we are in fact studying this at the moment but we don't really know the answer with certainty.

The likeliest explanation we believe has to do with vitamin D synthesis in the skin. As you know, when UV shines on our skin it participates as chemical synthesis of vitamin D.

Probably 100,000 years ago, this was an absolutely vital step in producing vitamin D. There were not very many dietary sources, only in a few unusual circumstances, and therefore if you happened at the time to live in a location where UV radiation is limited, such as a high latitude geographic place like, let's say northern Europe, then your ability to obtain sufficient vitamin D to live through childhood was probably highly dependent on the ability of UV to a) be delivered to your skin, b) and actually be absorbed into your skin.

And this is thought by many people to be the source, the evolutionary source, of light skin, individuals with light skin who don't tan very easily, I guess many of whom ended up, or their ancestors, moving to Australia.

That's one example we can think of where this, you know, the most ubiquitous, the most common carcinogen in the entire world here, apparently, is something that we are inclined to see. It's an amazing evolutionary paradox.

RACHEL CARBONELL: Dr Fisher says in modern times there are far safer ways of getting enough vitamin D through diet.

He says the research should be a consideration when it comes to devising health safety messages about the carcinogenic dangers of UV exposure.

DAVID FISHER: In terms of the public health impact, it would suggest to us that it may not be such a casual or simple thing to stop exposing oneself to UV radiation. There may actually be much stronger forces at hand that are guiding people to continue UV exposure.

RACHEL CARBONELL: Dr Fisher says the potential for addiction to UV radiation is probably greatest when it comes to commercial tanning beds, an industry which he says remains largely unregulated in the United States.

Craig Sinclair, from Australia's Cancer Council, says the research reinforces the wisdom of Australia's decision to phase out the commercial tanning bed industry.

CRAIG SINCLAIR: The really good outcome that we've had in Australia in recent years is a commitment by all state and territory governments to ban artificial tanning sun beds. And this is where we would more likely see the type of people who would be addicted to UV light because of the ease of access and their ability to be able to go at any time and expose themselves to UV to serve that addiction.

RACHEL CARBONELL: Craig Sinclair the study findings have long been suspected, but they add a layer of complexity to when it comes to imparting the sun smart message.

CRAIG SINCLAIR: Well, if this study adds to the weight, and I certainly believe it does, that frequent tanners can actually develop an addiction to ultra violet radiation, it means that it puts greater pressure on sun protection prevention campaigns to actually try and motivate these people away from being addicted to UV or to sunlight.

TANYA NOLAN: Craig Sinclair there from the Cancer Council ending that report from Rachel Carbonell.