The sweet spot: sleep length, sleep depth, & diabetes

You probably already know that there is a link between poor sleep hygiene and death. If we graphed this relationship, we'd get a "U-shaped" distribution. In other words, if your sleep duration is extreme - either extremely short or extremely long - your mortality risk increases.

In the middle of the graph, there is a "sweet spot", a zone that represents sleeping in moderation (7 to 8 hours each 24-hour day). Here, mortality risk dips to its lowest.

Many factors influence this U-shaped curve, and most scientists agree that one of these factors is diabetes. Research published in December confirmed that the relationship between sleep duration and type 2 diabetes is (what else?) a U-shaped distribution. Short sleepers and long sleepers are both at increased risk.

Why? It certainly appears that altering our sleep length changes our body chemistry. A quote from Science Daily's coverage: "Experimental studies have shown sleep deprivation to decrease glucose tolerance and compromise insulin sensitivity by increasing sympathietic nervous system activity, raising evening cortisol levels and decreasing cerebral glucose utilization. The increased burden on the pancreas from insulin resistance can, over time... lead to type two diabetes."

Now, new research suggests that the "sweet spot" goes beyond sleep length; sleep depth is also important. Restricting slow wave sleep (SWS) is enough to impair glucose tolerance, even when total sleep length is unaffected. Dr. Esra Tasali and colleagues at the University of Chicago recruited healthy, normal weight adults and let them sleep for 8.5 hours on two consecutive baseline nights.

But on the following three nights, the researchers disrupted any observed SWS by playing repetitive tones on bedside speakers, loud enough to cause arousal, but not loud enough to awaken the sleeper. Glucose tolerance dropped by 23%, even though cortisol levels appeared to be unaffected.

If you'd like to read more about the research, there is a nice article about it on MedPages. In the meantime, try to stay in that "sweet spot!"