While many ancient cultures worshipped solar deities, modern society has given the practice a whole new twist. Even though we know the dangers of too much sun, beaches are lined with people soaking it up; meanwhile, the CDC estimates that tanning salons are responsible for around 419,000 cases of skin cancer every year.

We all have seen the weathered, leathery effects of too much sun, and the terms “tanorexic” and “tanoholic” have entered the general lexicon; but what’s behind that unquenchable need for sun? A new study may hold the answer.

Earlier studies have looked into questions of addictive behavior in relation to tanning; they have found, for example, that blocking the opioid pathway in persistent tanners creates withdrawal-like symptoms. Other studies, according to Forbes.com, have concluded that regular indoor tanners can distinguish between UV light and non-UV light in tanning beds

The new study, published in the journal Cell, suggests that endorphins created by exposure to ultraviolet may be the cause. In lab experiments (not performed on humans), the researchers found that beta-endorphin levels rose with UV light exposure. They noted analgesic effects, presumably due to the opioid response; as well, the administration of opioid-blocking naloxone led to symptoms of withdrawal.

But why would we have an addiction to the sun and tanning? That answer is pretty simple. We are wired with an evolutionary drive for sunlight exposure as a means to synthesize vitamin D, the study notes. We’re programmed to like the feeling of the sun because it ensured that our ancient ancestors got their vitamins.

“Primordial UV addiction, mediated by the hedonic action of beta-endorphin and anhedonic effects of withdrawal, may theoretically have enhanced evolutionary vitamin D biosynthesis,” the scientists wrote.

And while the authors of the study were careful in their language – and many will debate whether or not we can really be addicted to sunlight – the researchers warned that UV addiction, “may contribute to the relentless rise in skin cancer incidence in humans.” It's a reminder that too much of anything, even good old sunlight, can be a bad thing.

Related stories on MNN: