Tuesday, October 29, 2013

Glucose Control vs Memory: When Good Enough Isn't

Don't ask me why or how but I must've stumbled upon a treasure trove dementia related studies recently, not unlike the blind squirrel finding the occasional nut.  In any case, I want to offer you an analogy to explain my philosophy towards health care.  When I was in grade school, then high school, and then college, the typical grading system went something like this: F = failure, D = low pass, C = average, B = high pass & A = honors.  Or something like that.  In other words, if all you wanted to do was pass, you could get by with a D grade.  After all, that D grade was good enough to move you on to the next grade or even towards graduation.  But for some of us, good enough just wasn't good enough.  If we wanted to become a doctor, we needed to get straight A's in college which meant straight A's in high school, etc.  Even a B grade wasn't good enough.

So think about Hemoglobin A1c, the running 3 month measure of sugar control.  I liken it to your average trip speed on a long drive whereby you speed up & slow down & speed up again, perhaps coming to a complete stop due to traffic, stop lights or stop signs.  Glucose, whether random or fasting, is represented in this scenario by your speedometer which tells you how fast you're going at that precise moment in time that you glance at it.  However, that very same speedometer tells you nothing about how fast you were going a minute ago, 5 minutes ago, 30 minutes ago, an hour ago, etc.  

Well, back in the day, "normal" A1c was any value less than 6.  Well controlled for a diabetic was 6-7 while poorly controlled diabetics had values greater than 7.  A few years ago, we tightened our perspective and declared normal as less than 5.6.  At risk for diabetes (also known as pre-diabetes) is now 5.7 to 6.4.  And greater than 6.4 is now considered consistent w/diabetes.  Notice the semantics as well as the reference ranges (which will vary slightly depending upon your lab).

With all this in mind, a cross-sectional study was published early online last week prior to print next month in Neurology in which the authors concluded that lower A1c within the normal reference range was associated w/better memory & larger hippocampal volume, a structure linked to Alzheimer's disease risk.  Now, before you go out and ask your doctor for insulin to lower your sugars, notice that this conclusion is based upon 141 participants, half of whom were women, average age 63yo.  This study says nothing about what happens if you lower your blood sugar.  It's not a double-blind, placebo-controlled, randomized trial.  Instead, the authors compared various domains of memory & cognition to A1c, blood glucose, insulin and magnetic resonance imaging scans.  Even in those without diabetes or impaired glucose tolerance, lower A1c was linked to better delayed recall, learning ability & memory performance.  Think about that before you take that next bite of food.

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