|Image 1: It looks awkward, but sleep masks|
and ear-plugs are effective, cheap and
save ways to improve sleep quality
(image from lackofsleepsymptoms)
Other than in the initially mentioned epidemiological guesswork ... ah pardon, correlation studies, Hursel et al. had their 15 healthy male volunteers report to the laboratory twice (>2 weeks between the sessions of the randomized, single-blind cross-over study). During each visit, the subjects stayed for 48 h in a respiration chamber, where energy expenditure, physical activity (radar), and substrate oxidation were meticulously measured. On both occasions, the subjects had ﬁxed bedtimes (lights out: 11:00pm; lights on: 7:40am) resulting in 8 h sleeping time per night. On one of the occasions, however, the scientists used induced sleep-fragmentation by the means of "approximately hourly wake-up calls" the subjects had to respond to by turning off their alarm after 2 min.
|Figure 1: Relative differences in carbohydrate and fat oxidation, as well as respiratory quotient (higher quotient = more carbohydrate dependent) in 15 healthy men as a consequence of interrupted sleep (data calculated based on Hursel. 2011)|
|Figure 2: Relative changes in total, resting (REE) and sleeping energy-expenditure (SEE), as well as absolute changes in activity induced energy expenditure (AEE) and overall caloric balance (data calculated based on Hursel. 2011)|
we showed an initial increase in physical activity and AEE as an effect of sleep fragmentation, mainly because the subjects had to turn off their alarm clock 7 times during the night. However, the resulting increased exhaustion and sleepiness during the subsequent day might eventually counter-balance physical activity and AEE.They go on to point out that the increased activity goes hand in hand with the increase in carbohydrate oxidation, the depletion of glycogen stores and the (this is my assumption) stress-related -52% decrease in fatty acid oxidation (cf. figure 1).
The real-world results of this unhealthy combination of non-regenerative sleep, daytime exhaustion and sleepiness and the accompanying abstract metabolic shifts are cognitive problems, a lack of motivation (esp. to work out or do any physical work), carb-cravings, snack-attacks & co... In your efforts to (re-)feed a body that is unable to access his well-stocked fat reserves, you end up overcompensate the initially increased energy expenditure, constantly provoking insulin spikes which totally blunt fat oxidation, trigger temporary hyperglycemia (if you are not already diabetic) and induce further snack-attacks. Thus, you are triggering a down-ward spiral that is especially hard to escape from, if your body does not get the chance to reset his insulin and stress levels in the course of a good nights sleep - keep that in mind before you place your cell-phone next to your pillow in order to "keep in touch" with your (facebook-)friends 24/7, as a very recent study published in the journal SLEEP showed that "mobile phone use for calling and for sending text messages after lights out was associated with sleep disturbances independent of covariates and independent of each other" (Munezawa. 2011).