It’s Gonna Be a Bright, Bright, Bright, Sunshiny Day

Summer has arrived, and with it, lots and lots of sunshine. Americans love sunshine and flock to it whenever we can.
But sunshine isn’t an unmitigated benefit. Dangers lurk in those rays. Most of us know by now that harmful UV (ultraviolet) light can be toxic, and we use sunscreen (more or less religiously) to deter the most harmful effects. The CDC (the U.S. Centers for Disease Control and Prevention) recommends avoiding prolonged exposure to the sun and wearing sunscreen with a minimum of 15 SPF.
So what else is new? Well, a raft of recent studies has in fact produced some brand-new information about sunshine.
First, researchers at Harvard have turned up startling evidence that may explain why some people don’t restrict their time in the sun even though they’re aware of the dangers. It seems that basking in those UV rays can be addictive. According to a new study from Harvard Medical School, investigators at Mass General Hospital have found that chronic UV exposure raises “circulating levels of beta-endorphin” in mice, and that mice who become accustomed to those levels exhibit “withdrawal symptoms” when the beta-endorphin activity is blocked.
What is beta-endorphin? Most of us have heard of endorphins, powerful neurotransmitters that originate in the human body, controlling emotions and often blocking pain. A “beta-endorphin” is one kind of endorphin, considered to be not only stronger than morphine as a pain-blocker but also producing feelings of pleasure. Beta-endorphin is much like an opioid, a/k/a an opiate, a drug used by the medical profession to treat pain. Opioids/opiates impact the brain, leading to feelings of intense pleasure, and addiction—both physical and mental—can develop very quickly.
According to lead researcher David E. Fisher, the Wigglesworth Professor and Chair of Dermatology at HMS and Mass General, the Harvard study found that UV radiation produced “opiate-like effects, including addictive behavior.” The study, reported in the June 19 issue of Cell, may explain what Fisher calls “the ‘sun-seeking’ behavior that may underlie the relentless rise in most forms of skin cancer.”
The study uncovered mounting evidence of addictive behavior among humans as well as mice. Several studies have noted addiction-like behavior in people using indoor tanning facilities. Other studies found that an “opioid blocker” produced withdrawal-like symptoms in these frequent tanners.
Let’s look at what the Harvard researchers did. For six weeks, they delivered a daily dose of UV light—equal to the exposure of fair-skinned humans to 20 or 30 minutes of midday Florida sun—on the shaved backs of a group of mice. Within a week, levels of beta-endorphin in their blood rose significantly. The levels remained elevated during the study period, gradually returning to normal only after UV exposure ended. When the researchers administered naloxone, an “opioid blocker” known to block opioid-pathway activity, the mice had such classic symptoms of opioid withdrawal as trembling, shaking, and teeth-chattering.
Fisher concluded that humans might react the same way, noting that “a natural mechanism reinforcing UV-seeking behavior may have developed during mammalian evolution.” Why? Probably because we synthesize vitamin D (increasingly viewed as an essential nutrient) from the UV light in sunshine. Low blood levels of vitamin D can lead to a host of ailments. But sun-seeking behavior, Fisher warned, carries with it “the carcinogenic risk of UV light.” Other sources of vitamin D, like cheap oral supplements, more safely and accurately maintain healthy vitamin D levels.
Fisher concluded that because persistent UV- seeking appears to be addictive, reducing skin-cancer risks may require “actively confronting” hazardous behavior like indoor tanning. Although both the CDC and the FDA have indicted indoor tanning as highly dangerous, Fisher fears the “passive risk-messages” we’re using aren’t good enough. In other words, we need to use much scarier warnings to let addicted sun-lovers know how destructive their behavior is.
At the same time, there’s new information that not enough sun exposure can also be risky. The July issue of the Journal of Internal Medicine reported on a study conducted in Sweden suggesting that the CDC guidelines may be too restrictive in regions with limited sunshine. The Swedes tracked sun exposure in 30,000 light-skinned Swedish women ages 25 to 64 from 1990 to 1992, gathering a wealth of information, including time spent sunbathing and the use of tanning beds. When national statistics were later reviewed in 2011, it appeared that women who got the most sun had the greatest risk of developing skin cancer. No big surprise there. But it was surprising that women who avoided the sun were twice as likely to die from any cause, including skin cancer. The risk of dying from all causes was twice as great among the sun-avoiders and 40 percent higher in those with moderate sun exposure. The study didn’t include information on blood levels of vitamin D or the use of vitamin D supplements, but its results may actually support the Harvard conclusions. If exposure to sunshine leads to better health overall, maybe that’s because sunshine leads to higher vitamin D levels. If so, our focus should probably shift to ensuring that everyone gets enough vitamin D, regardless of sun exposure.
Finally, if you’re a confirmed sun-lover, you might want to know about another study, this one conducted at Northwestern Medical School. Researchers found that people who are exposed to even moderately bright morning light have a significantly lower body mass index (BMI, based on height and weight) than those who had their first exposure later in the day. According to lead author Kathryn Reid, the earlier the light exposure, the lower one’s BMI. Senior author Phyllis Zee, director of the school’s Sleep and Circadian Rhythms Research Program, noted that light is the “most potent agent to synchronize your internal body clock,” regulating circadian rhythms, which in turn “regulate energy balance.” In short, if you want to lower your BMI, you might want to get outside between 8 a.m. and noon (20 to 30 minutes should do it).
Summing up, “I can see clearly now….”
For people like me (a redhead with extremely light skin), the less sun exposure the better. Although I love being outside on a sunny day, I use lots of sunscreen and stay in the shade as much I can. I make up the vitamin D deficit by taking an inexpensive supplement every morning.
For everyone else, the studies pretty much reinforce what we already knew. They suggest keeping your sun exposure within bounds. Some time in the sun is fine, so long as you use some sunscreen. Avoid overdoing your exposure via indoor tanning, and otherwise avoid addictive sun-seeking behavior. But one way or another, don’t forget to get some vitamin D.