An Excursion To Miss
Most people with diabetes know that keeping their blood sugar levels as close to normal as possible prevents or delays the onset of diabetes complications, including eye complications. The Diabetes Control and Complications Trial (DCCT) proved that intensive diabetes management, resulting in lower average blood glucose values (glycosylated hemoglobin or HbA1c), dramatically lowered the risk of eye, kidney, and nerve disease in people with type 1 diabetes. The United Kingdom Prospective Diabetes Study (UKPDS) found the same beneficial result in people with type 2 diabetes. In fact, further analysis of these two landmark studies shows that for HbA1c levels between 5% and 8%, each ten percent reduction in HbA1c (for example, lowering HbA1c from 8% to 7.2%) reduces the risk of diabetic retinopathy progression by more than 40% (above an HbA1c level of 8%, the reduction in risk is even greater). This finding is crucial, because diabetic retinopathy is the leading cause of severe visual impairment and blindness in working-age Americans. What is less widely appreciated, however, is the extent to which fluctuating blood sugar levels increase the risk of developing diabetic retinopathy and having the disease worsen over time.
By fluctuation, I mean the extent to which a person’s blood glucose levels go up and down during the course of a day. This variability, euphemistically referred to as “glycemic excursions,” is now believed to be quite important in the development of diabetes complications. It is critical to remember that HbA1c is an average, and tells us nothing about the number and extent of our highs and lows, our blood sugar ups and downs, our glycemic excursions. For example, a patient with five blood glucose readings measuring 105, 110, 115, 104, and 116 will have an average (or ‘mean’) blood glucose level of 110 (add the numbers up and divide by 5). Another patient with readings of 50, 170, 40, 230 and 60 will also have an average blood glucose of 110. Obviously, this second patient has a great deal more fluctuation in his readings than does the first patient, and researchers now believe that this sort of difference places our second, hypothetical patient at considerably higher risk for diabetes complications. Because HbA1c is really nothing more than a fancy measurement of average blood glucose levels, people with identical HbA1c levels may, in fact, have significantly different risk profiles for complications, including vision loss.
Good clinical evidence for this position can be inferred from the DCCT. Even with identical HbA1c values, patients in the “intensively managed” group (more frequent monitoring of blood glucose levels combined with multiple daily injections of short-acting insulin or use of an insulin pump to correct and minimize ‘glycemic excursions’) developed diabetic retinopathy much less often than patients in the “conventionally managed” group (less frequent blood glucose monitoring combined with only one or two daily insulin injections, resulting in more blood sugar variability). For example, over a ten-year period, patients in the “intensive” group with an HbA1c of 8% developed retinopathy 60% less often than patients in the “conventional” group with the same HbA1c level of 8%; the averages were the same, but the results were dramatically different. The UKPDS did not show this difference, however, presumably because “intensively managed” patients in this study were given long-acting insulin only, rather than short-acting insulin necessary for minimizing ‘glycemic excursions.’
The point here is to be aware of the importance of keeping our blood glucose levels as close to normal as possible, with as little variability as possible, in order to minimize our risk. Variability is measured statistically by the “standard deviation,” a value reflecting how much the numbers making up any given average go up and down. For blood glucose levels, a lower average (HbA1c) and a lower standard deviation are better. Most home blood glucose meters now come with software that calculates standard deviation, and I would encourage every person with diabetes to discuss this with his or her diabetes doctors. The new wave of continuous glucose monitoring systems will also give patients a new tool for recognizing, correcting, and preventing our ‘glycemic excursions,’ and more research into the significance of blood glucose variability is under way. After all, there are countless other much more pleasant ‘trips’ that we’d all like to take.
For more information on diabetic eye disease, consult Dr. Chous’ book Diabetic Eye Disease: Lessons From a Diabetic Eye Doctor, Fairwood Press, Seattle, 2003.
Read more about Dr. Chous here.
Visit Dr. Chous' website here.
NOTE: The information is not intended to be a replacement or substitute for consultation with a qualified medical professional or for professional medical advice related to diabetes or another medical condition. Please contact your physician or medical professional with any questions and concerns about your medical condition.
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