The body's decreased response to insulin beginning as early as age 13 may mean increased cardiovascular disease risk by age 19, according to research reported in Hypertension: Journal of the American Heart Association.
The finding indicates that the prevalence of atherosclerotic cardiovascular disease risk factors and type 2 diabetes (both of which are related to obesity and are increasing as today's children reach adulthood) also are related to insulin resistance independent from obesity, said Alan R. Sinaiko, M.D., lead author of the study and professor of pediatrics at the University of Minnesota Medical School in Minneapolis. After screening blood pressure, height and weight in more than 12,000 5th through 8th grade students in Minneapolis public schools, 357 students (average age 13) were recruited for the study. Two-hundred twenty-four participants completed the study. The participants were 58 percent male and 83 percent white.
At baseline the children underwent a complete physical examination including measurements of blood pressure, height, weight, percentage of body fat, high density lipoprotein cholesterol (HDL-C), triglycerides and fasting insulin levels. The students were also categorized by stage of sexual development. Sinaiko and colleagues tracked insulin resistance with a series of insulin clamp studies first at age 13, then 15 and again at 19.
"The insulin clamp is considered the gold standard to measure insulin resistance, a precursor to type 2 diabetes," Sinaiko said. "Insulin regulates sugars, starches, fats and proteins in the body. When cells become resistant to the effects of insulin, insulin levels increase to regulate metabolism." This clamp technique infuses insulin and glucose into the blood and measures the resulting glucose and insulin levels. Those who require lower amounts of glucose, indicating lower uptake of glucose into muscle cells, were considered insulin resistant, he said.
The insulin clamp tests were repeated at age 15 on 309 participants and again at age 19 on 224 participants. Occurring together, insulin resistance, high blood pressure, low HDL-C, high triglycerides and obesity are defined as the metabolic or insulin resistance syndrome, which Sinaiko and other researchers say may trigger type 2 diabetes and atherosclerosis. Sinaiko said the correlation between insulin resistance at age 13 and age 19 was highly significant. Insulin resistance at age 13 predicted high systolic blood pressure, which is associated with risk of stroke, and high triglycerides at age 19. For every unit increase in insulin resistance there was a 0.41 millimeters of mercury (mm Hg) increase in systolic blood pressure and 1.91 milligrams per deciliter (mg/dl) increase in triglycerides. "This is the first study to show insulin resistance by itself is a significant predictor of cardiovascular disease, beginning in childhood," Sinaiko said.
Co-authors are: Julia Steinberger, M.D.; Antoinette Moran, M.D.; Ching-Ping Hong, M.A.; Ronald J. Prineas, M.D., Ph.D.; and David R. Jacobs Jr., Ph.D. The National Institutes of Health funded the study.
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