Glycemic Variability: The Damaging Effects of Uncontrolled Blood Sugar

Due to the current epidemic of type II diabetes, everyone knows that having sustained high blood sugar is detrimental to health.  Chronic high blood sugar leads to a wealth of issues, including nerve damage, arterial damage, and loss of vision [1].  However, sustaining high blood sugar is NOT necessary for blood sugar levels to damage your health.  Research suggests that extreme glycemic variability is as detrimental, if not more damaging, to health and mortality risk.

Glycemic Variability and the Research

Glycemic variability is the short term fluctuation of blood sugar.  The average healthy individual experiences daily blood sugar changes within a third of his/her average level (i.e. a range of 25 mg/dL for a person with an average level of 75), but people with high glycemic variability can experience fluctuations that are greater than 50% of average levels.  In a review of studies on glycemic variability [2], researchers had this to say about the magnitude of damage with high variability:

Glycemic variability seems to have more deleterious effects than sustained hyperglycemia in the development of diabetic complications...

Specifically, researchers say that large swings in blood sugar levels can have greater effects on endothelial function (ability of the blood vessels to expand or constrict to meet cardiovascular needs) and oxidative stress, which plays a large role in heart disease, plaque formation, and Alzheimer's.

What really caught my eye with glycemic variability was a study with ICU patients over a 10 year period at Stamford Hospital [3].  I could tell you about the results, but the charts below tell a much better story.  Tables A and B divide the patients up in regards to whether or not they were diabetic before being admitted.  The values at the bottom are average glucose levels (70-99 is desired and the rest have different degrees of elevated blood sugar).  The vertical measure is percentage of mortality.  The bars at each average glucose level separate individuals by coefficient of variation (A.K.A. amount of blood sugar variation, with green being the smallest and red the largest).

As you can see, the red bars are significantly higher than the others for people of healthy or slightly elevated blood sugar levels, meaning there was a strong link between mortality and high glycemic variability.  Researchers found this relationship to be statistically significant "even after adjustment for severity of illness." 

Interpreting the Data for Personal Application

The latter study was obviously performed on hospitalized patients, so it's unclear whether those results apply to those of us who are healthy.  Ultimately, here's what I take away from the studies presented:

1. Just because a person generally has desired blood sugar levels, it doesn't mean that he or she is free from the effects of blood sugar-spiking foods.
2. This is possibly another way that strength training is cardio-protective.  Having more muscle mass translates into having more storage space for glucose.  This added storage space will limit the degree of blood sugar spikes from high sugar meals.  
3. Finally, taking the last study as literal as possible, if you find yourself in the hospital for any serious illness, avoid simple carbohydrates and sugary foods like the plague!  Your life may depend on it.