*2.6. The Role of Tracking in Increased CV Risk in Adulthood*

There is a strong correlation between childhood and adult obesity, and a large number of obese children transfer their adiposity into adulthood. Obese children and adolescents are five times more likely to become obese adults. About 55% of obese children continue being obese in adolescence, around 80% of obese adolescents will continue being obese in adulthood, particularly those suffering from severe obesity. About 70% of them will continue being obese over the age of 30 [126–128]. Age of the child, severity of obesity, and presence of parental obesity affect the tracking of obesity into adulthood. Most adolescents with obesity will continue being obese in adulthood, as persistence of obesity transfer into adulthood is associated with older age. In children under the age of 10, the risk of being obese is doubled if they have obese parents [129].

On the other hand, childhood and adolescent BMI is not a good predictor of adult obesity incidence. Only 20% of adults with obesity were obese as children or adolescents, and over 80% of obese people over the age of 30 were not obese as adolescents. Therefore, BMI has poor sensitivity to predict adult obesity [127]. Childhood obesity is not the only and primary factor that contributes to adult obesity. Adult obesity carries an increased risk of CVD. The link between obesity and CVD is explained by the CVD risk-factor profile that is often observed in obese adults. The profile includes increased rates of dyslipidemia, HTN, as well as T2D. Childhood obesity is a CVD risk-factor, and may lead to early atherosclerosis and premature CVD in adulthood. Even though CVD rarely manifests itself until adulthood, CVD risk factors have been observed in childhood [130]. HTN, dyslipidemia, impaired glucose metabolism, as well as systemic inflammation, have all been associated with vascular changes in childhood. If not adequately treated, they may contribute to an increased risk of adverse CV events in adulthood [131]. Nevertheless, it is important to determine what kind of independent effects childhood obesity has on CVD in adulthood. Many studies and meta-analyses have been conducted, all pointing to obese children being at higher risk for obesity as adults [132,133]. However, a large number of studies did not considered the effect of adulthood-incurred obesity, so it is impossible to form a precise conclusion of the relationship between childhood obesity and CV events in adulthood [134]. Studies that took into consideration the effect of obesity incurred in adulthood on CV events pointed to the fact that the effect of childhood obesity, as an independent factor, might not be great [135]. Those studies showing an association of obesity in childhood with CVD in adulthood, identified weight as a significant independent determinant [65].

However, there are other factors in favor of an association of early obesity with increased CVD risk:

Atherogenesis, a process leading to the development of atherosclerosis begins at an early stage of life [136]. Obesity in childhood accelerates this process and causes changes in blood vessels, especially in adolescence. The earliest sign of atherosclerosis is the appearance of fatty streaks, and atherosclerotic wall lesions are in direct connection to childhood obesity [136–138].

Clustering of CVD risk factors has been highly associated with obesity in childhood, including increased systolic blood pressure, elevated LDL-C, elevated TGs and reduced HDL-C [138,139].

Obesity with multiple CVD risk factors during adolescence is associated with an almost 15-fold increased risk of developing CVD before the age of 50 [140].

In an extensive study conducted on 276,000 children, Baker et al. note that an increased BMI in childhood correlates with the appearance of CVD in adults, and at the same time isn't related to an increased BMI in adults [141].

BMI in late adolescence is directly related to atherosclerosis in middle age measured by coronary angiography—this relationship persisted even when BMI was adjusted for adults, as well as CVD risk factors [142].

Childhood obesity is a moderate risk-factor for adult obesity-related morbidity. However, the risk increase is not significant enough for childhood BMI to serve as a reliable predictor of the incidence of adult morbidities [132].

It is important to note, that the risks of T2DM, HTN, dyslipidemia, and carotid-artery atherosclerosis among overweight or obese children who became nonobese by adulthood were similar to those among persons who were never obese [143].

Table S1 summarizes the given evidence for tracking of CV risk factors from childhood to adulthood.
