A new study published in Cell suggests that excessive exposure to sunlight leads to addiction-like behavior in mice.
The study aimed to determine the relationship between UV exposure and levels of beta-endorphins. Beta-endorphins are the “feel good” hormones that increases the pain threshold. Beta-endorphins replicate the numbing effects of opioid drugs.
To conduct the study, researchers exposed mice to UV radiation for six weeks. The UV radiation was comparable to a moderate amount of midday summer sun exposure for lighter-skinned individuals. After the exposure to UV radiation, they measured the levels of beta-endorphins.
They found that levels of beta-endorphins and pain threshold increased significantly in UV-exposed mice compared to mice not exposed to UV.
In another experiment, the researchers administered Naloxone to the mice who had been exposed to the UV. Naloxone is a drug used to counter the effects of opiate overdose.
The injection elicited withdrawal symptoms such as shaking, teeth chattering, and jumpiness. This implies that the mice became physically dependent on UV radiation.
The researchers speculate that this addiction-like behavior may be caused by a behavioral motivation to seek vitamin D from UV radiation.
“Our results may also imply a potential evolutionary beneﬁt of an endogenous mechanism that reinforces UV-seeking behavior,” the researchers stated. “A recent study has shown activation of known reward centers in the brains of volunteers during UV exposure.”
The researchers call for further studies to evaluate beta-endorphin action in the human brain to determine how it relates to sun-seeking behavior.