Too much sun could make you a UV addict, raise cancer risk

It is common knowledge that exposure to sunlight helps the skin synthesise vitamin D. But at the same time prolonged exposure can also lead to skin cancer. The degree to which people expose themselves to the sun varies from region to region and culture to culture. For example, in India, people generally avoid sunlight to prevent darkening of skin but people in countries like the US do just the opposite—they spend hours basking in the sun. So, while it is debatable whether we should spend time in the sun at all or how much exposure is safe, a new study shows that sunlight can actually be addictive. In that case neither the fear of skin cancer nor dark complexion has the power to keep people away from the sun, it would seem.

The study reveals that chronic exposure—as little as six weeks, five days a week—to the sun causes the release of feel-good hormones or endorphins that compel people to have an instinctive desire to laze around in the sun.

"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," says David Fisher of Massachusetts General Hospital and Harvard Medical School who led the study. "We suspect that the explanation involves UV's contribution to vitamin D synthesis in the skin,” he added.

The experimentation was carried out by testing mice by treating them with UV light and mock UV rays after shaving them to measure their average tanning ability. After 1 week, significant elevations in circulation of b-endorphins were observed, for the UV treated mice whereas no significant changes in plasma b-endorphin were observed in mock-UV-treated mice.

The mice were the placed in white and black boxes. It was observed that the UV treated mice avoided the black boxes and were constantly attracted to light, whereas this behaviour was not seen in the mock UV treated mice. Thus an addiction to the sunlight was observed in the post conditioned mice.

In rodents, another b-endorphin, an enzyme, is synthesised in skin that elevates the plasma levels after being exposed to a low-dose UV. This subsequently increases the pain-related thresholds, making them tolerate higher levels of pain, increasing the urge of these rodents to spend more time in the rays of the sun.

The team found that the effect of exposure to sun was similar to the impact of drugs like opium and leads to dependence. After the six week period ended, treatment with an opioid-blocking drug, which blocks the receptor present on the surface of the cell, making the cell believe that opioid isn't available, caused withdrawal symptoms, including shaking, tremors, and teeth chattering, in mice that had been exposed to UV light. The findings are published in June 19 issue of Cell.

While this study would suggest that people should avoid the sun, lack of exposure could lead to vitamin D deficiency. Fisher said Vitamin D levels are usually maintained in people by a combination of sun exposure and dietary intake. “However, the sun exposure component can be highly variable (such as during different seasons of the year or different amounts of time spent in the sun— or varies for people with dark and light skin). Utilizing oral supplements (vitamin D pills) is a safer means to maintaining vitamin D levels because they do not increase cancer risk, whereas UV/sunlight clearly does,” he said.

Research: Skin β-Endorphin mediates addiction to UV light

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