The better the weather is, the worse I sleep. When spring hit last week, it brought tossing, turning and a deeper understanding of the blue denim futon to which I was exiled after one too many tosses. Or maybe it was the turns that set my wife off, it's hard to tell.
Anyway, as the weather turned nasty this weekend, I rolled back into full hibernation mode, waking up on Saturday rested after a week of insomnia.
The rapid switch underscored something I'd noticed recently: I sleep like an overweight woodchuck in winter, while summer is always a caffeine-riddled sleepless haze. Which is a bummer, as coffee just doesn't taste as good when it's 96 degrees out.
To puzzle out exactly what's keeping me up, I pulled up night-time temperatures for the past few months, and marked the nights during which I couldn't sleep. As it turns out, my comfort zone sits at around 40 degrees. Anything above that and I'm toast.
Why? I had no idea. It seems almost random. So, in desperation, I turned to science. Scientists study sleep and temperature quite often, whether it be in rats with bits of their brain scrambled or in menopausal women. Groups which, as it turns out, are more similar than you might think. Researchers do so because temperature is a huge determinant of sleep quality; research shows that it's harder to sleep through heat or cold than it is through noise.
This makes sense because during the deepest sleep, the body loses some of its ability to regulate temperature. According to a 1994 French study, the ideal temperature for sleep is several degrees below the ideal waking temperature. For someone who is awake and clothed, the most comfortable temperature is between 72 and 78 degrees. It varies based on weight and other factors. For example, someone sleeping in bed wearing pajamas and covered only with a sheet is happiest between 60 and 66 degrees.
In theory, that's also where my thermostat is set. But I also live in a cut-rate apartment where the landlord's idea of insulation is an extra coat of taupe paint over the 1954-vintage interior wood paneling. We've got a furnace, but it merely squeals like a boiling woodchuck and spews heat into the one room in the apartment we never use, the unfinished laundry room. In the summer, it's worse. We've got a venerable window-mounted air conditioner, but as far as I can tell its only function is to flood the kitchen and quadruple our electric bills.
Some might consider this situation subpar, but I prefer to regard it as an ad hoc sleep lab. Our bedroom is so sensitive to outside temperatures that we'd probably be better insulated from the elements if we just set up a yurt in the middle of Stephens park.
Somehow, when all the sheets, paneling and woodchucks are figured in, it appears that an outside temperature of 40 or below leads to something around personal ideal temperature underneath the comforter. And that's why I slept so well this weekend.
Light also influences circadian rhythms and sleep, of course, but a Japanese study indicates that daylight savings and the changing of the seasons are at most bit players in my insomnia.
In 1987 and 1988, researchers tricked 10 male Japanese students into spending one 4-day weekend each season in their little sleep lab, where they were exposed to outside light but kept indoors at a temperature between 68 and 75 degrees Fahrenheit.
The researchers found that the men tended to sleep a bit more in winter despite the constant temperature, but the change wasn't enough to be statistically significant. They did, however, find something else interesting and perhaps even relevant.
Body temperature drops as much as a degree from its daytime high to the depth of REM sleep. Oddly, the study found that the timing of that drop seems to have something to do with the seasons. In the spring and summer, body temperature dropped before the men went to sleep. In the fall and winter, it didn't fall until they had hit the hay.
But all those details obscure the study's one gigantic problem, an issue which comes up often in these studies. In my opinion, it's significant enough to invalidate every last one of them. It's one tiny sentence, but it changes everything. If you're mid-breakfast, I recommend finishing before reading on. Ready? Here goes: Throughout the study period, "rectal temperature was continuously monitored."
Ouch. I can't conceive of a single situation in which those words and normal daily life could coexist. I'm skeptical that those dudes manage to sleep at all, let alone produce results that have any correlation to the circumstances in which I sleep each night.
Fortunately, researchers in Greece hit on a slightly less weird and intrusive way to study sleep patterns. They compared daily records from the Athens University Medical School in 1989 (a cool year) with those from 1994 (a hot year). They found a "considerable increase" in visits to the psychiatric emergency room caused by sleep disturbance during the many consecutive hot days of 1994.
In fact, the researchers found a significant relationship across the board: The hotter it gets, the more likely sleep-disturbed patients are to flood into the psychiatric emergency room. To be honest, I don't blame them. A few more days above 40, and I might become a statistic myself.
Andrew Van Dam is a graduate student at the Missouri School of Journalism.