Does summer make you depressed?

Like its winter twin, the summertime version of seasonal depression could be described as an exaggerated version of the way the seasons make most of us feel, according to the scientific literature. Winter depressives tend to eat a lot and sleep a lot; summer depressives, on the other hand, lose their appetite and struggle with insomnia. So it's kind of like the pattern most brains and bodies follow — even people without these conditions feel sleepier in winter and have a harder time sleeping in the longer days of summer — but in both summer and winter depressives, it reaches a "pathological extreme," as the authors of one of the earliest journal articles on summer depression, published in 1991, phrased it.

Summer SAD is not as common as the winter version, which itself only affects an estimated 5% of Americans, said Norman Rosenthal, a professor of psychiatry at Georgetown University School of Medicine who was part of the research team that first identified both versions of seasonal affective disorder. The summer kind is thought to account for just 10% of all SAD cases, by some estimates. And because it's uncommon, summertime SAD has largely been overlooked by scientists who study seasonal affective disorder. "In the 25 years since it was first described, SAD has been the subject of more than one thousand studies," writes Joseph Kasof in a 2009 paper on summer-onset depression in the Journal of Affective Disorders. "However, SAD researchers have narrowly focused on winter-SAD ... very little was learned about summer-SAD."

Consequently, scientists don't have a good idea of how to treat summertime depression. Winter SAD can usually be managed with light box therapy — brief, daily exposure to a light that simulates daylight — since the disorder is thought to be triggered by the season's lack of sunlight. But it's not clear what, exactly, causes summertime depression: Is it the heat, or too much sunlight, or both? Anecdotally, at least, it seems to be the bright light. "Some of these people say things like, The light cuts through me like a knife," Rosenthal said.

For summer depressives, the best guess scientists currently have is to take the opposite approach: stay inside, curtains drawn, fans and air-conditioning operating at full blast. Even still, any relief gained is fleeting, Rosenthal said. "The trouble with cold therapy, which might be seen as the equivalent of light therapy, is that it doesn't seem to last," Rosenthal said. "If you're in the cool air conditioning, it helps you while you're in it, but then when you go outside — my patients have described it as being hit by a wall of heat." Any benefit gained from the time indoors in the cool disappears, he said.

With winter depression, there is at least the small comfort that everyone else is hunkered down in their apartments watching Netflix, too. Summer depression, on the other hand, can feel isolating, like you're missing out on some big party. "They're hiding in their dark rooms, and they feel like they're not part of this great pageant that's going on outdoors, in the swimming pools and going for hikes," Rosenthal said.

According to the National Alliance on Mental Illness, an even smaller fraction of people experience seasonal depression in both summer and winter, "while feeling fine each fall and spring, around the equinoxes." More evidence that the world would be a happier place if it were around 65 degrees, forever and always.

By Melissa Dahl, The Science of Us