Ask a Science Blogger: Are we happier in the summer?

My gut response after reading this question was: Well, duh--obviously, summer is more conducive to happiness. I mean, you can make a good case for the virtues of spring and fall, but they're really less seasons than they are opening acts. And apart from Christmas and skiing, winter doesn't have a whole lot to recommend it. Nope. If you're ranking seasons, summertime is the clear winner. Summer=hot sun, slow, quiet afternoons, and water-logged family vacations. What more does a human being need to be happy, apart from an air-conditioner and an ample supply of snacks?

Proving my theory seemed simple enough. All I had to do was find out the "happiness ratings" of people lucky enough to live in the handful of politically stable locales that enjoy perpetual summer. It stood to reason that the happiest people on earth would live in places like Hawaii, Belize, and the Bahamas, right?

Not so much, as it turns out. In fact, researchers at the University of Leicester recently performed a meta-analysis of surveys on well-being and satisfaction, and after totaling up 80,000 responses from people across the globe, they found that the four happiest places on earth are: Denmark, Switzerland, Austria and - wait for it - Iceland. Viewed through this lens, it appears that happiness has far less to do with sun than it does with beer consumption and good healthcare.

Now, I'm a fan of both beer and state-subsidized medicine, but this just seems wrong. The sun has to have something to do with well-being, doesn't it? The answer is: Sort of. There's plenty of evidence to suggest that the sun makes people happier--but only if they're depressed to begin with. For instance, exposure to the sun or other sources of light does wonders for people who suffer from Seasonal Affective Disorder (SAD), a syndrome that causes 4 percent to 6 percent of the general population to go into a deep funk in the winter months.

Sidenote: I know what you're thinking. If you buy the argument that a lack of sun contributes to SAD, wouldn't people in places like Switzerland and Denmark be more prone to SAD and therefore-well, you know . . . sadder? Again, the answer is frustratingly inconclusive. If you look at the world as a whole, people at higher latitudes, who experience fewer hours of daylight in winter, do as a rule have higher rates of SAD, but there's a huge amount of variation from country to country.

Denmark, for instance, has a relatively high rate of SAD, 12.4 percent, as do the northern reaches of New York State, 12.5 percent. But the Swiss oddly have a rate of only 2.2 percent and they aren't much lower than Denmark latitude-wise. Iceland, which is extremely far north, has a rate of just 3.6 percent. Scientists speculate that Icelanders have developed a genetic immunity to SAD, but the truth is that no one really knows what the heck is going on. (Want to tie your brain in a knot? Here's the source of these stats.)

The question remains: Why does sunlight, and thus summer, do wonders for some of us? When sunlight hits your skin it triggers the production of Vitamin D. Some scientists speculate that a small portion of the population depends on Vitamin D to stay emotionally afloat, because several studies have shown that a deficit of Vitamin D is correlated with a dip in mood. (See here and here.)

But sunlight's no one-trick pony. In addition to spurring the production of Vitamin D, it also suppresses the production of melatonin, the chemical that regulates our body clocks when the seasons change. (For more on this read SciBlogger Nick Anthis's recent piece " A Sun Ray A Day . . .) Some researchers theorize that in winter months, the lack of sunlight screws with people's internal clocks, compromises their sleep patterns, and leaves them vulnerable to depression.

But that's not all. Still other researchers claim that sunlight ups the amount of serotonin in the brain. Serotonin - for those of you who've managed to blip over the media hype - is the neurotransmitter many scientists believe to be the culprit behind depression. According to this theory, some people's depressive symptoms are alleviated when the sun is out, because their serotonin-manufacturing system kicks into a high gear.

So which is it? At this point, researchers are confident that melatonin plays a role in Seasonal Affective Disorder, but beyond that, we don't know. SAD might be a genetic vulnerability activated by a combination of all of the above. Science is still figuring that out.

In meantime, if you find yourself falling into an emotional morass come winter, it's safe to say a vacation in the tropics won't hurt. As for the rest of you, might I recommend a frosty beer and some socialized medicine?