Blood Sugar, Diabetes, Insulin Resistance and Metabolic Syndrome
According to the American Heart Association, "Heart disease is the leading complication and cause of death among diabetes patients, yet many of them do not understand the risk or its cause." Adults with diabetes are two to four times more likely to have heart disease or suffer a stroke than adults without diabetes. And even though 63 percent of diabetes patients eventually develop cardiovascular disease, a recent survey found that among diabetics, only 33 percent consider heart conditions to be among the "most serious" diabetes-related complications.1 Barely over half (57 percent) the patients were aware that insulin resistance is associated with heart disease.
This lack of knowledge occurs despite the abundant clinical and experimental evidence showing a strong relationship between dysglycemia and heart disease. For years, researchers have known that high blood sugar levels from diabetes can damage nerves that help regulate the heart's ability to sustain a steady beat, impairing what's known as "autonomic control." Eventually, this damage can lead to an out-of-whack pulse (arrhythmia), a "silent" heart attack causing permanent cardiac injury, or even sudden death. Thus, as fasting glucose levels rise, so does the risk of cardiovascular events and related deaths, even at slight elevations in healthy non-diabetic individuals.2,3
Growing scientific evidence suggests that there is no arbitrary point at which imbalances of glucose and insulin become clinically significant. Instead, the health risks posed by dysglycemia occur over a continuum: "Metabolic risk factors for type-2 diabetes mellitus and for cardiovascular disease worsen continuously across the spectrum of glucose tolerance categories, beginning in the lowestÉfasting glucose level."4 Hemoglobin A1c is an important indicator of long-term glucose control, while fructosamine reflects average glucose levels over a shorter time period (10-14 days). High levels of these markers have been implicated in cardiovascular disease complications associated with Type-2 diabetes.5
Studies also suggest that damage to the heart may actually begin long before full-fledged diabetes appears, and may be mediated not just by blood sugar imbalances, but by early disruptions of a insulin response. Subtle abnormalities in insulin and glucose metabolism are associated with higher risk of cardiovascular disease and mortality.6,7
According to a recent study funded in part by the National Institutes of Health, increased levels of fasting insulin, even among healthy non-diabetic adults between the ages of 25 and 44, correspond with impaired autonomic control of the heart. As fasting insulin levels rose in the subjects, their successive R-waves measured on an electrocardiogram (ECG) tended to move closer together, indicating an increased risk of heart-related nerve damage, arrhythmia, and sudden death.8 These relationships show why it's important for healthcare practitioners to identify and treat all known cardiovascular risk factors in patients with or at-risk of developing type-2 diabetes.
1 American Heart Association News Release; May 21, 2001. Available at: http://www.americanheart.org/What_News/AHA_
2 Bjornholt JV, Erickssen G, Aaser E, Sandvik L, Nitter-Hauge S, Jervell J, Erikssen J, Thaulow E. Fasting blood glucose: an underestimated risk factor for cardiovascular death: results: results from a 22-year follow-up of healthy nondiabetic men. Diabetes Care 1999;22(1):45-49.
3 Coutinho M, Gersetin HC, Wang Y, Yusuf S. The relationship between glucose and incident cardiovascular events: a metaregression analysis of published data from 20 studies of 95,783 individuals followed for 12.4 years. Diabetes Care 22(2):233-240.
4 Meigs JB, Nathan DM, Wilson PW, Cupples LA, Singer DE. Metabolic risk factors worsen continuously across the spectrum of nondiabetic glucose tolerance. The Framingham Offspring Study. Ann Intern Med 1998;128(7):524-533.
5 Raj DSC, Choudhury D, Welbourne TC, Levi M. Advanced glycation end products: a nephrologist's perspective. Am J Kidney Dis 2000;35(3):365-380.
6 DECODE study group. Glucose tolerance and mortality: comparison of WHO and American Diabetes Association diagnostic criteria. Lancet 1999;354:617-621.
7 Barzilay JI, Spiekerman CF, Wahl PW, Kuller LH, Cushman M, Furberg CD, Dobs A, Polak JF, Savage PJ. Cardiovascular disease in older adults with glucose disorders: comparison of American Diabetes Association criteria for diabetes mellitus with WHO criteria. Lancet 1999;354:622-625.
8 Watkins LL, Surwit RS, Grossman P, Sherwood A. Is there a glycemic threshold for impaired autonomic control? Diabetes Care 2000;23(6):826-30. On-line at http://journal.diabetes.org/FullText/DiabetesCare