Why sunshine is as addictive as heroin

lifestyle concept - beautiful happy woman enjoying summer outdoors

Sunshine acts like an addictive drug and has a similar effect on the body as heroin, scientists claim.

Ultraviolet (UV) rays from the sun stimulate the production of endorphins, "feel good" hormones that act on the same biological pathway as opioid drugs, research shows.

The study suggests that the desire to bake for hours on a beach involves more than topping up a tan.

It may appease our craving for a sunshine "fix", in much the same way as an addict satisfies a yearning for heroin or morphine.

Lead scientist Dr David Fisher, from Harvard Medical School in the US, said: "This information might serve as a valuable means of educating people to curb excessive sun exposure in order to limit skin cancer risk as well as accelerated skin ageing that occurs with repeated sun exposure.

"Our findings suggest that the decision to protect our skin or the skin of our children may require more of a conscious effort rather than a passive preference."

Experts had known that sun-seeking behaviour can fit the clinical criteria for a substance-related disorder. But what underlay this apparent "addiction" had been unknown until now.

Dr Fisher and his team investigated links between UV exposure and the opioid receptor pathway in "naked" laboratory mice.

After a week in the artificial sunshine, endorphin levels in the blood of shaved animals increased.

At the end of six weeks, the mice were given an opioid-blocking drug, naloxone. Abruptly denied the drug-like effects of UV, they suffered an array of withdrawal symptoms, including shaking, tremors and teeth chattering.

In addition, UV exposure caused the animals' tails to stiffen and lift up - an effect also seen when mice are given opioid drugs.

When the mice were removed from the UV rays the symptom, known as "Straub tail", gradually faded away.

Mice not exposed to UV light did not display the same responses.

"It's surprising that we're genetically programmed to become addicted to something as dangerous as UV radiation, which is probably the most common carcinogen in the world," said Dr Fisher, whose findings appear in the journal Cell.

"We suspect that the explanation involves UV's contribution to vitamin D synthesis in the skin.
However, in the current time, there are much safer and more reliable sources of vitamin D that do not come with carcinogenic risk, so there is real health value in avoiding sunlight as a source of vitamin D."

British experts urged caution when extrapolating the results of the research to humans.

Dr Clare Stanford, reader in experimental psychopharmacology at University College London, said:
"This study does not provide the sort of evidence needed to show addiction to UV light in mice and it is even less certain that the work predicts addiction in humans.

"This would require testing whether the mice preferred UV light or non-UV light, which was not done in this paper.

"The strain of mice used in this experiment produce virtually no melatonin, which is thought to protect against damage from UV light. Shaving such mice and exposing them to UV light raises important ethical questions about animal welfare and again casts doubt on the relevance of the results to humans."

Dr Richard Weller, senior lecturer in dermatology at the University of Edinburgh, said: "Mice are nocturnal animals, covered in fur, which avoid the light, so one must be cautious about extrapolating from these experiments to man.

"Nonetheless, the authors discuss some literature suggesting that a similar pathway might also be present in man.

"It is very unlikely that evolutionary pressures would select for a trait which reduces survival and reproductive 'fitness'. If an 'addiction' to sun truly also exists in mankind, it suggests to me that there is a benefit to it.

"The authors mention vitamin D, but in addition to this, epidemiological data (particularly from Scandinavia) show that increased sun exposure is associated with reduced all-cause mortality.

"Our recent work shows how sunlight reduces blood pressure independently of vitamin D, which may account for some of the health enhancing effects of sun."

10 top holiday destinations to check out this autumn
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Why sunshine is as addictive as heroin

'America's Venice,' Fort Lauderdale, FL, offers a blissful escape for families (Walt Disney World is a few hours' drive away) and couples alike, thanks to crystal-clear beaches and hip hotels and eateries. Looking for adventure? Everglades National Park is an hour's drive and is ideal for camping, canoeing and getting up-close with crocodiles.
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Experience 'fijaka' (blissful contentment) in Split, on Croatia's south Dalmatian coast. Walk along white pebble beaches, kayak in blue waters, explore fishing villages and discover Roman ruins before island-hopping on Vis, Brač and party-favourite Hvar.
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With the Brandenburg Gate, Berlin Wall, Jewish synagogue and so much more, there is plenty for the history buff to soak up in this eclectic city. Progressive and hip, the nightlife is also worth an exploration, whether you're after thumping techno, chilled-out beer gardens, chic cocktails or unexpected burlesque.
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Denmark's capital city is a must-see combining medieval beauty with stunning avant-garde design, delicious food and hip hangouts. Perfect as a romantic city-break or family getaway, the city's September temps hover in the mid-teens, so grab a light jacket when you take in the sights and festivals on one of the city's many cycle paths. 
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The city's docks, formerly the site of criminal executions, now house ultra-hip design hotel The Thief, where you can rest your head after walking around museums, parks and the city's 19th-century buildings. Take a dip in the fjord for an electrifying experience before a treat from Kokosbollen, the chocolate-coconut snowball factory. Yum.
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Make the most of the low-20s climate and diminishing crowds in this Côte d'Azur city, which has plenty of attractions (museums, shopping, beaches) of its own. It makes an ideal starting point for exploring glitzy St. Tropez and Monte Carlo, as well as smaller villages like nearby Eze and artist haven St-Paul-De-Vence.
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Revel in the city's diverse architecture, from medieval Gothic to Antonio Gaudí's modernist masterpieces in this amazing Catalan city. Soak up the rays at Barceloneta Beach for a lazy relaxation session by the water one day; the next, get active with a sightseeing tour - with a twist - by exploring the city in a GPS-guided GoCar
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September is the perfect time of year to visit this idyllic Balearic Isle with glorious beaches and a fabulous old town dotted with tasty tapas bars and dominated by a striking Gothic cathedral. A great family-friendly destination, take the kids on a glass-bottomed boat tour and to the nearby Alcudia water park.
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Soak up the Polish capital's stunning attractions (Baroque palaces-meet-Communist-blocks) in a city with plenty of history and heartache, which has been restored since its almost-total destruction in WWII. Eat like a local and try the cheese and potato-stuffed dumplings (known as pierogi) at Pierogarnia na Bednarskiej.
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Take a stroll around the battlements of this ancient fortress city, surrounded by sparkling blue waters, and don't miss the medieval attractions of the Old Town (like the Franciscan Monastery, which houses the world's oldest pharmacy). For some early autumn sunshine, hit Banje Beach or the Miramare Bay.
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