Physical Activity Mitigates Insulin Resistance and Type 2 Diabetes in Juveniles
The burgeoning overweight and obesity problem in Americans of all ages has brought with it an increase in other lifestyle-related health problems. For example, in adults, obesity increases risk of mortality (4). More specifically, mortality from combined diabetes and kidney disease is significantly increased in both overweight and obese adults (3). Research shows that increased exercise capacity in adult men reduces all-cause mortality (7). Indeed, one study showed that exercise capacity more strongly predicts mortality in adult men than any other recognized risk factors for cardiovascular disease studied (7).
Overweight and obesity is now a recognized problem in American children and adolescents. One source reported that 13 to 14 percent of 6-11-year-old children and 12-19-year-old adolescents are overweight (9). Additionally, as a child’s age and degree of obesity increases, the chances that the child will become an obese adult likewise increase (9), bringing with it an increase in all-cause mortality (3). In juveniles, increased body mass index (BMI) is associated with an increase in insulin resistance (IR) (5, 10). But, IR is more closely associated with visceral adiposity than BMI alone (2). Girls are more insulin resistant than boys, and older or more overweight children are more insulin resistant than their younger or more normal weight peers (5, 10).
As mentioned, exercise capacity in adult men is a strong predictor of mortality (7). Certainly health-related risks for mortality are a concern, but equally concerning are the lifestyle-related diseases, once only seen in adults, which now are manifest in overweight and obese children and adolescents. Two interrelated issues are insulin resistance syndrome (IR) and type 2 diabetes.
Insulin resistance syndrome is characterized by an impaired ability for plasma insulin to clear glucose from the bloodstream, control hepatic glucose production, and suppress very low density lipoprotein production (9). Type 2 diabetes includes hyperglycemia and hyperinsulinemia due to the inability of insulin to bring about glucose uptake from its target tissues. Type 2 diabetics also suffer from polyuria, polydipsia, and peripheral neuropathy (9).
Some research indicates that whereas pancreatic β-cell function is closely associated with family heredity, insulin resistance is not (8). Rather, insulin resistance is very closely associated with overweight and obesity in children and adults. The combined effects of impaired β-cell function and insulin resistance in children with low acute insulin response and glucose disposal index can lead to the development of type 2 diabetes mellitus (8).
Type 2 diabetes is preventable (9). Studies have shown that changes in lifestyle-related factors such as diet and exercise can result in a significant reduction in progression to diabetes in adults with impaired glucose intolerance, and in adults with a history of diabetes (9).
The news is also good for children and adolescents with IR and type 2 diabetes. For example, relatively high-intensity exercise can bring about beneficent changes in cardiovascular and metabolic health in obese adolescents. Kang et al. (6) found that high-intensity exercise training can result in beneficial changes in a number of insulin resistance syndrome markers such as cardiovascular fitness, total cholesterol/HDL ratio, LDL particle size, and diastolic blood pressure. High intensity physical activity (PA) [75-80% of peak oxygen uptake (VO2)] was more effective at improving insulin resistance syndrome markers in obese juveniles than moderate PA (55-60% peak VO2), despite the same calorie (kcal) expenditure per session (250 kcal/session) (6).
Furthermore, in accordance with the dose-response relationship of exercise and health benefits, adolescents with “especially unfavorable” cardiovascular and metabolic health risks stand to benefit the most from exercise (6). Even without a change in body weight or composition, exercise can decrease IR in juveniles (1).
For example, Bell et al. (1) found that children and adolescents (between the ages of 9 and 16 years) with high fasting insulin levels who engaged in eight weeks of circuit training, but who did not change any aspect of their current dietary practices, lost no significant amount of weight but did experience significant improvements in aerobic fitness and insulin sensitivity. That such changes were elicited in children and adolescents without any concomitant modifications in diet indicates that even greater improvements in aerobic fitness and insulin sensitivity could be expected with more comprehensive lifestyle and behavior changes.
Imperatore et al. (5) assessed the insulin sensitivity of 1,783 adolescents (ages 12-19 years) and compared the data to survey data collected in 1999-2000 for the National Health and Nutrition Examination Survey (NHANES). They found that in both boys and girls, lower insulin sensitivity was correlated with higher BMI values. The boys surveyed showed higher levels of habitual PA than the girls. When analyzed for relationships between PA, cardiovascular fitness, and insulin sensitivity, independent of BMI, the data indicated that in boys PA and cardiovascular fitness were correlated with high insulin sensitivity but the same correlations were not found in girls. Imperatore et al. (5) postulated that the difference between boys and girls in their study results could be due to an overall greater need by girls for increased levels of PA to decrease their insulin resistance.
A study by Young-Hyman et al. (10) may shed some additional light on the difference between boys and girls and insulin resistance. One-hundred and eleven African-American children between the ages of 5- to 10-years were administered an oral glucose tolerance test. Comparison of the glucose tolerance test results to anthropometric measurements for the subjects revealed that in general, insulin levels in the children rose with age and weight, irrespective of gender. In general, girls produced more insulin than did boys. If girls of all races exhibit a general trend toward greater impaired glucose tolerance levels than boys, then this could explain the hypothesis of Imperatore et al. (5) that girls may need higher levels of PA to control their naturally higher insulin resistance.
In summary, in the face of an increasing prevalence of overweight and obesity in children and adolescents and an increasing incidence of IR and type 2 diabetes, lifestyle-related behavior changes can and should become part of prevention and treatment plan utilized by medical and health professionals. Exercise training and habitually high physical activity levels are effective means to manage weight and control IR and type 2 diabetes in children.
Although additional research is needed to further elucidate the precise mechanisms by which physical activity and other lifestyle-related factors effect their influence on the etiology of IR and type 2 diabetes, enough is known about the benefits of physical activity and the quality and quantity of physical activity to bring about beneficial effects that one need not wait for further research to begin to improve one’s quality of life right now.
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