Body-Mass Index in Adolescents

Posted by • June 24th, 2016

2016-06-17_10-36-07Overweight and obesity in adolescents have increased substantially in recent decades and affect a third of the adolescent population in some developed countries. Twig et al. assessed the risk of fatal cardiovascular events in adulthood according to the body-mass index range during adolescence, using a national database of 2.3 million Israeli adolescents in whom height and weight were measured between 1967 and 2010.

In this study, a range of values for body-mass index that were well within the accepted normal range in adolescence predicted increased cardiovascular and all-cause mortality during 40 years of follow-up. A new Original Article summarizes.

Clinical Pearl

• In developed countries, how do trends in cardiovascular mortality among young adults compare to those among older age groups?

In contrast to the steep decline in the rate of death from cardiovascular causes among older age groups, cardiovascular mortality among young adults has not decreased or the decline has slowed in several developed countries.

Clinical Pearl

• Is the association between body-mass index and increased risk of subsequent cardiovascular mortality limited to those who are overweight or obese?

Some, although not all, studies suggest that a BMI that falls within the upper-normal range in adolescence is associated with an increased risk of death from cardiovascular causes, although a determination of the BMI threshold that is associated with such an increased risk remains uncertain.

Morning Report Questions

Q: Is there evidence of an association between an adolescent BMI in the mid-normal range and an increased risk of subsequent cardiovascular mortality?

A: The large size of the study by Twig et al., which incorporated more than 42 million person-years of follow-up, provided adequate statistical power to assess the associations within the currently accepted normal range of BMI values. Excess all-cause mortality (including cardiovascular mortality) starting at the 50th percentile of adolescent BMI values confirmed the findings of an earlier study on a portion of this cohort. Thus, the classification of BMI according to the accepted normal range (i.e., the 5th to 84th percentiles and a BMI ranging from 18.5 to 25.0) may underestimate the risk associated with being overweight in adolescence. This inference is supported by findings of the current study of Twig et al. that there is a graded increase in the risk of death starting at the mid-normal range of adolescent BMI (50th to 74th percentiles) and that the high-normal BMI range (75th to 84th percentiles) was associated with hazard ratios of 2.2 for coronary heart disease and 1.8 for total cardiovascular causes.

Table 2. Duration of Follow-up and Cause of Death, According to Percentile of BMI during Adolescence.

Table 3. Hazard Ratios for Cause of Death, According to Percentile of BMI during Adolescence.

Figure 2. Body-Mass Index (BMI) during Adolescence and Subsequent Cardiovascular Mortality.

Q: Does the association between cardiovascular mortality and increased BMI in adolescence take decades to become evident?

A: Twig et al. found that, in calculations of the risk of death from total cardiovascular causes at different follow-up times and 10-year intervals, the association between cardiovascular mortality and increased BMI was evident by 10 years of follow-up (hazard ratio, 2.0; 95% CI, 1.1 to 3.9) and was more pronounced during the follow-up period from 30 to 40 years (hazard ratio, 4.1; 95% CI, 3.1 to 5.4).

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