Animal study: sunbathing is addictive
If you sunbathe or use sunbeds compulsively, you may be addicted to ultraviolet radiation. Researchers at Harvard Medical School published an animal study in Cell, which shows that addiction to ultraviolet light shows a resemblance to addiction to morphine and related drugs.
Each year the number of people diagnosed by doctors as having skin cancer increases by three percent, and this is mainly because they voluntarily expose themselves to more sunlight than is good for them. Might this be because sunlight or synthetic UV radiation is addictive?
The question is less far-fetched than you might at first think. Exposure to UV light causes skin cells to produce the natural painkiller beta-endorphin. This substance reacts with the mu-opioid receptor, as do drugs such as opium and morphine.
The researchers exposed mice, whose fur on their backs they had shaved off, for six weeks almost every day to UV light for half an hour. And indeed, as a result the concentration of beta-endorphin in the mice's blood rose. When they were exposed to light that had no UV radiation [Mock], this did not happen.
Naloxone is a substance that blocks the mu-opioid receptor. Administration of this substance did not stop UV light from boosting the beta-endorphin concentration. UV light also made the mice less sensitive to pain.
If you give rodents substances that affect the mu-opioid receptor, their tail stands up straight. It's called a 'Straub tail'. The photo below on the left shows a rat under the influence of an opioid. The rat on the right is not.
Exposure to UV light caused the mice to display a Straub tail more often.
If UV light does imitate the effects of an opioid, then stopping exposure to it should cause withdrawal symptoms. And indeed: when the researchers injected their mice after six weeks of UV radiation with the endorphin blocker naloxone, the mice showed signs of withdrawal symptoms in their behaviour.
"The current studies suggest that UV exposure is biologically addictive but dangerous due to UV's mutagenic activities toward formation of all common forms of skin cancer", the researchers conclude. "This calls into question the perceived safety of tanning beds and current benign views of indoor tanning, reflected in the United States’ current Food and Drug Administration classification of UV-emitting devices as class I and therefore minimally regulated."
"It may be necessary, therefore, to more proactively protect individuals, including teens, from the risks of an avoidable, potentially life-threatening exposure and to view recreational tanning and opioid drug abuse as engaging in the same biological pathway."
Cell. 2014 Jun 19;157(7):1527-34.
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