Do you ever check the weather app and feel like you have to be outside when the sun's shining? There may be a neurological explanation behind that: Ultraviolet rays can stimulate signs of addiction similar to recreational drugs, according to a new study published in the journal Cell.
Previous studies have suggested that people can be addicted to soaking in UV rays, but little was known about the mechanisms behind this condition. See, UV exposure releases beta-endorphins in the body, which bind to opioid receptors—neurotransmitters that signal pain relief in your brain. Researchers hypothesized that this might explain addictive behavior—similar to how drugs such as heroin, morphine, and painkillers create that temporary "feel-good" sensation—with sunlight.
So to test their theory, study authors experimented with mice that were exposed to UVB rays for five days a week over six weeks total. Each day, they were exposed to the equivalent of about 20 to 30 minutes of midday sun exposure for people. Beta-endorphin levels in the bloodstream increased by the end of the first week and remained high before returning to normal levels a week after the experiment.
Next, researchers checked to see if the mice would demonstrate withdrawal symptoms after being injected with an opioid-blocking substance called naloxone, which is commonly used to treat drug addiction overdose. Turns out the rodents did experience these withdrawal signs—such as shaking, teeth chattering, and tremors.
Then, they wanted to see if these withdrawal symptoms were major enough to influence the animals' behavior, so they gave them access to both a dim box and a bright box. Interestingly, the mice experiencing withdrawal symptoms were more likely to go to the bright box, even though mice in general prefer dark environments. Basically, they responded to UV exposure like a drug, and when they weren’t getting it anymore, they sought it out.
More research is needed to determine if this impacts humans in the same way and if there's a way to counteract this "sun addiction." But for now, this might explain why some people—who are fully aware of the risks of sunlight overexposure—still consciously choose to bask in UV rays or visit a tanning bed, says lead study author David Fisher, M.D., Ph.D., chairman of the department of dermatology at Massachusetts Medical Hospital.