I had no idea this many Americans were nocturnal:
Twenty percent of American workers are night-shift workers, and the number is growing by about 3% per year, according to the Bureau of Labor Statistics. While the rest of society sleeps, police officers, security guards, truck drivers, office cleaning crews, hotel desk clerks, nurses, pilots and many others keep patients alive, streets safe and packages moving. But at a price.
These workers — and people with more conventionally sleep-deprived lifestyles — are known to be at higher risk for accidents, sleep disorders and psychological stress due to daytime demands, such as family and other obligations, that interfere with sleeping. Now scientific evidence suggests their disrupted circadian rhythms may also cause a kind of biological revolt, raising their likelihood of obesity, cancer, reproductive health problems, mental illness and gastrointestinal disorders.
The evidence for an increased cancer risk is so compelling that, in December, the International Agency for Research on Cancer, a unit of the World Health Organization, declared that shift work is “probably carcinogenic to humans.”
Natural selection has invested a lot of effort in our circadian rhythms, so it’s a little distressing to learn that 20 percent of us are flagrantly violating all those CLOCK genes.
The news isn’t all bad, however. Over at Mind Matters, we just featured some new research which demonstrates the surprising power of power naps. Even if you can’t get eight hours of sleep during the wee hours of the morning – and people on the night-shift sleep significantly less – you can make up for the lack of sleep with short bursts of non-REM sleep:
In this study, 18 college students participated in three different experimental conditions: taking a long nap (35 minutes), a short nap (six minutes) or remaining awake. Prior to napping (or remaining awake), participants learned a list of 30 words and were tested on these words one hour later. Learning always took place at 1 P.M. and testing took place at 2 P.M.; the question was whether napping would produce better memory retention than wakefulness. The short nap consisted of relatively light sleep, mostly stages 1 and 2 non-rapid eye movement (NREM) sleep. The long nap contained even more of this light sleep, along with about 10 minutes of deeper slow-wave sleep (stages 3 and 4 NREM). Similar to a previous study by Tucker et al. (2006), the long nap resulted in better memory for the words than wakefulness. But, remarkably, so did the short nap, albeit at a lower level. Nevertheless, this suggests that just six minutes of sleep can produce significant memory benefits.
What no one can figure out, though, is why even short naps can have cognitive benefits. After all, the neural mechanisms that underlie the consolidation of new memories are believed to take at least sixty minutes – protein synthesis takes time. What, then, is going on? Jessica Payne and Matthew Walker hypothesize:
One possible answer resides in the electrical signals of sleep. For example, short nappers obtained a few minutes of stage 2 sleep, a stage that produces “sleep spindles.” These powerful synchronous bursts of electrical activity have been linked to memory stabilization. Alternatively, such short naps may not necessarily change the strength of the memory, but rather allow easier access to it. That is, sleep, and just a small amount, may “grease” the recall-shoot that memories slide down, allowing easier access to the material. Yet another idea is that ultra-short naps may rapidly refresh regions of the prefrontal lobe (which suffer the greatest burden when sleep deprived), and, as a result, allow the brain to more accurately search its storehouse of memories.