A study published today shows that type 1 diabetics often miss episodes of hypoglycemia during sleep; this finding may or may not come as a surprise to most type 1's. I used to assume that low BG's always, or at least usually, woke me up. At least, I had woken up plenty of times with that heavy, weak feeling and rushed for the nearest dose of sugar. But when I started wearing the DexCom, and waking up to the low BG alarm far more than expected, I realized my assumption was wrong. Confirming my own observations, an article published today in PLoS (Public Library of Science) Medicine suggests that nocturnal hypoglycemia unawareness may be a much more common problem than previously assumed. In the article, "Defective Awakening Response to Nocturnal Hypoglycemia in Patients with Type 1 Diabetes Mellitus," Schultes, Jauch-Chara et al., compare the response to hypoglycemia (2.2 mmol/L plasma or 35 mg/dL whole blood) induced in 16 type 1's and 16 controls during stage 2 of sleep. Only 1 out of 16 diabetics woke up, in comparison to 10 out of 16 controls (6.2% vs 62%), which was significant statistically. In all research subjects who woke up, a significant increase in epinephrine blood concentration was seen, on average, 7.5 minutes prior to waking. (Epinephrine is a one of the "fight-or-flight" hormones that is released in response to stress.) The type 1's showed a weakened or absent epinephrine response. The article also discusses other counterregulatory hormones, such as glucagon, which was higher in the controls than in the type 1's.
Again, I was really surprised how many times that low BG alarm has gone off during the night with my DexCom, especially after a big day of exercise or a change in my normal routine. I remember one night after a particularly long bike ride when I repeated three cycles of waking to the DexCom alarm, eating, and falling asleep again. Whether I would have woken up eventually can't be determined from that experience; but since the DexCom woke me up each time, I definitely would have had a more severe low BG without it.
I had stopped using the DexCom because I ran out of sensors and didn't want to fork over $175 for another 5-pack. But maybe this will encourage me to do so. And I definitely plan on quoting this study in my letter to my insurance for CGM coverage.
I originally read about this story on ScienceDaily's medical headlines: "Patients With Type 1 Diabetes Don't Wake In Response To Hypoglycemia." They wrote a good summary of the study. Another easily understandable summary is on the front page of the original article.