In principle, a careful experiment should be able to isolate the effects of sleep deprivation by depriving people of sleep in the absence of stress and other such confounding variables. That seems to be what this experiment does, but as I read the article closely, I found myself unsure that the effects it reports are necessarily due to sleep deprivation per se.
I realize that a brief summary article like this does not provide all the details of the experimental methodology, but a couple of things that were reported in the article struck me as curious. The researchers studied physical functioning (cortisol levels, etc.) in men who had a normal night’s sleep (eight hours in bed) the first three nights of the study, followed by a period of sleep deprivation (four hours in bed) the next six nights of the study, and finally a period of sleep recovery (12 hours in bed) the last seven nights of the study. InAnother potential problem comes from the sequential nature of the different sleep conditions. All participants had normal sleep, then sleep deprivation, then sleep recovery (in that order). Therefore, the three conditions differ not only in the amount of sleep, but also in the level of familiarity with the experimental procedures. Why should that make a difference? Well, consider the results reported for the stress hormone cortisol. In comparing people who are sleep deprived (days 4-9 of the study) with those who are in sleep recovery (days 10-16 of the study), they are comparing people early in the experiment to those later in the experiment. If the experimental procedures are themselves stressful (e.g. drawing a blood sample) then a person who has been through it more often might find it less stressful, and therefore not respond so strongly. This fact, rather than the amount of sleep itself, might explain the pattern of results in the physiological data.
I’m not sure whether the methodological issues I’ve raised really do account for all the...