Monday, October 27, 2014

Blood sugar targets

or how low should I go? How high is too high? Is having targets even a good idea for Adaptive Management?

I came across this interesting post on what constitutes a "normal" range for blood sugar from Steve Cooksey. I like his assertion that "NORMAL BLOOD SUGAR RANGES should not increase the risk of dementia ... cell or organ damage." Seems like a good starting point to me. So this 2012 study in the American Journal of Neurology Steve found is alarming to me:
Those with higher fasting blood sugar levels within the normal range and below 6.1 mmol/l (or 110 mg/dL) were more likely to have a loss of brain volume in the areas of the hippocampus and the amygdala, areas that are involved in memory and cognitive skills, than those with lower blood sugar levels.
Why alarming? Because first thing in the morning my fasting sugar levels are usually higher than 110 mg/dL (the "dawn phenomenon"). Dang. That means my brain might be shrinking faster than I'd like. My fasting sugar levels later in the day (like now, 5pm, 85 mg/dL) are usually much better. I've had fasting sugar levels as low as 78 mg/dL, but not very often. Post-prandial (after eating) I can get spikes much higher than that.

Steve has another whole page devoted to justifying his blood sugar targets, with links to lots of studies showing everything from increased risks of dementia to organ damage even when blood glucose levels are at "pre-diabetic" levels. His goals are for fasting sugar to be between 60-90 mg/dL, and post-prandial levels less than 120 mg/dL or better, less than 100 mg/dL. In fact, there's a study showing that people with post-prandial glucose levels greater than 87 mg/dL had decreases in coronary lumen diameter (figure reprinted here). Essentially, having high blood glucose after eating clogs your arteries.

So the question is, should I adopt these blood glucose targets? The problem with setting a target on an objective is that it can unduly limit one's thinking, especially if there are trade-offs between the objective with a target and other objectives. Robin Gregory et al (2012) have a really good discussion of this point in a section called "The Trouble with Targets". If I set a fixed target of post-prandial glucose less than 100 mg/dL, then I immediately rule out options that say, reliably get me to 101 mg/dL but also improve other objectives. Like, degree of satisfaction with my diet, or a lower Triglyceride to HDL ratio. In the case of recommendations by the American Diabetes Association, fasting BG levels less than 130 mg/dL are considered "acceptable", despite abundant evidence that levels that high are still doing extensive harm.

So rather than set a firm target, the solution is to recognize that the utility of lower blood glucose increases steadily with decreasing blood glucose, even after I pass thresholds that are considered "acceptable" by the medical community.

Gregory et al. (2012) Structured Decision Making. Wiley-Blackwell, West-Sussex, UK.

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