A new mouse study has found that continuous exposure to ultraviolet (UV) radiation causes the release of endorphins, known as feel-good hormones, leading to physical dependence, tolerance, and addiction-like behavior in the rodents.
This could explain why people have an instinctive desire to be in the sun, despite its known health risks, according to researchers.
“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 aging that occurs with repeated sun exposure,” said senior study author David Fisher, M.D., Ph.D., of Massachusetts General Hospital and Harvard Medical School.
“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.”
According to the researchers, skin cancer is the most common form of cancer in the United States. Additionally, those who seek out the sun and UV rays through tanning beds often meet the clinical criteria for a substance-related disorder, the researchers noted.
One reason may be that UV exposure stimulates the production of endorphins, which relieve pain by activating opioid receptors through the same pathway activated by prescription painkillers, morphine, and heroin, they explain.
In the new study, Fisher and his research team examined whether this pathway could underlie UV addiction. They exposed shaved mice to UV light for six weeks and found that endorphin levels in the bloodstream increased within a week.
At the end of the six weeks, treatment with an opioid-blocking drug caused withdrawal symptoms in the mice, including shaking, tremors, and teeth chattering.
This led the mice to avoid the location where they were given the drug, suggesting that chronic UV exposure produces physical dependence and addiction-like behavior, according to the researchers.
“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,” Fisher said. “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.”
The study was published in the journal Cell.
Source: Cell Press