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Educating the Student Body
loss of 5-10 percent of body weight through calorie restriction and exercise
has been shown to reduce the risk of cardiometabolic disease by improv-
ing risk factors (Diabetes Prevention Program Research Group, 2002;
Ross and Janiszewski, 2008). In particular, weight loss results in reduced
visceral adipose tissue, a strong correlate of risk (Knowler et al., 2002),
as well as lower blood pressure and blood glucose levels due to improved
insulin sensitivity. Even without significant weight loss, exercise can have
significant effects in adults by improving glucose metabolism, improving
lipid and lipoprotein profiles, and lowering blood pressure, particularly for
those who are significantly overweight (Ross and Bradshaw, 2009). Similar
benefits have been observed in adolescents.
A growing body of literature addresses the associations of physical
activity, physical fitness, and body fatness with the risk of metabolic syn-
drome and its components in children and especially adolescents (Platat
et al., 2006; McMurray et al., 2008; Rubin et al., 2008; Thomas and
Williams, 2008; Christodoulos et al., 2012). Studies in adults have shown
that higher levels of physical activity predict slower progression toward
metabolic syndrome in apparently healthy men and women (Laaksonen
et al., 2002; Ekelund et al., 2005), an association that is independent of
changes in body fatness and cardiorespiratory fitness (Ekelund et al., 2007).
Few population studies have focused on these relationships in children
and adolescents, and the use of self-reported activity, which is imprecise in
these populations, tends to obscure associations. In a large sample of U.S.
adolescents aged 12-19 in the 1999-2002 NHANES, for example, there
was a trend for metabolic syndrome to be more common in adolescents
with low activity levels than in those with moderate or high activity levels,
although the differences among groups were not statistically significant
(Pan and Pratt, 2008). Moreover, for each component of metabolic syn-
drome, prevalence was generally lower with higher physical activity levels,
and adolescents with low physical activity levels had the highest rates of all
metabolic syndrome components.
The association between cardiorespiratory fitness and metabolic syn-
drome also was examined in the 1999-2002 NHANES (Lobelo et al.,
2010). Cardiorespiratory fitness was measured as estimated peak oxygen
consumption using a submaximal treadmill exercise protocol, and meta-
bolic syndrome was represented as a “clustered score” derived from five
established risk factors for cardiovascular disease, an adiposity index, insu-
lin resistance, systolic blood pressure, triglycerides, and the ratio of total
to HDL cholesterol. Mean clustered risk score decreased across increasing
fifths (quintiles) of cardiorespiratory fitness in both males and females. The
most significant decline in risk score was observed from the first (lowest)
to the second quintile (53.6 percent and 37.5 percent in males and females,
respectively), and the association remained significant in both overweight
Copyright © National Academy of Sciences. All rights reserved.
Educating the Student Body: Taking Physical Activity and Physical Education to School
Relationship to Growth, Development, and Health
127
and normal-weight males and in normal-weight females. Other studies,
using the approach of cross-tabulating subjects into distinct fitness and
fatness categories, have examined associations of fitness and fatness with
metabolic syndrome risk (Eisenmann et al., 2005, 2007a,b; Dubose et al.,
2007). Although different measures of fitness, fatness, and metabolic syn-
drome risk were used, the results taken together across a wide age range
(7-18) show that fitness modifies the influence of fatness on metabolic syn-
drome risk. In both males and females, high-fit/low-fatness subjects have
less metabolic syndrome risk than low-fit/high-fatness subjects (Eisenmann,
2007).
That many adult chronic health conditions have their origins in child-
hood and adolescence is well supported (Kannel and Dawber, 1972; Lauer
et al., 1975; Berenson et al., 1998; IOM, 2004). Both biological (e.g.,
adiposity, lipids) and behavioral (e.g., physical activity) risk factors tend to
track from childhood and especially adolescence into adulthood. Childhood
BMI is related to adult BMI and adiposity (Guo et al., 1994, 2000;
Freedman et al., 2005), and as many as 80 percent of obese adolescents
become obese adults (Daniels et al., 2005). Coexistence of cardiometabolic
risk factors, even at young ages (Dubose et al., 2007; Ramírez-Vélez et al.,
2012), has been noted, and these components of metabolic syndrome also
have been shown to track to adulthood (Bao et al., 1994; Katzmarzyk et
al., 2001; Huang et al., 2008). Landmark studies from the Bogalusa Heart
Study (Berenson et al., 1998; Li et al., 2003) and others (Mahoney et al.,
1996; Davis et al., 2001; Morrison et al., 2007, 2008) have demonstrated
that cardiometabolic risk factors present in childhood are predictive of
adult disease.
The benefits of exercise for prevention and treatment of cardio-
metabolic disease in adults are well described (Ross et al., 2000; Duncan et
al., 2003; Gan et al., 2003; Irwin et al., 2003; Lee et al., 2005; Sigal et al.,
2007; Ross et al., 2012). Prospective studies examining the effects of exer-
cise on metabolic syndrome in children and adolescents remain limited, and
it is important to refrain from extrapolating intervention effects observed in
adults to youth, although one might reasonably assume the benefits in older
adolescents to be similar to those in young adults. Indeed, based on the
inverse associations of physical activity and physical fitness with metabolic
syndrome (Kim and Lee, 2009) and on the available intervention studies,
some experts have recommended physical activity as the main therapeutic
tool for prevention and treatment of metabolic syndrome in childhood
(Brambilla et al., 2010). Comparative studies in adults have shown that the
effect of exercise on weight is limited and generally less than that of calorie
restriction (Brambilla et al., 2010). Moreover, the relative effectiveness of
diet and exercise depends on the degree of excess fatness (Brambilla et al.,
2010). Comparative studies in children and youth are few, as behavioral
Copyright © National Academy of Sciences. All rights reserved.
Educating the Student Body: Taking Physical Activity and Physical Education to School
128
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