shows that in childhood but not adulthood, male subjects had higher mean values for fitness and lean body mass than female subjects. Mean fitness increased for females but not male subjects from childhood to adulthood, and BMI increased substantially for both.
Summary of study variables in childhood and adulthood
indicates that there is a clear association between increasing composite child-adult fitness and mean step count (P = 0.007). Pedometer step count was associated with adult fitness (P < 0.001).
Daily step counts and relative fitness in adulthood according to changes in fitness from childhood to adulthood
shows that for each unit increase in child fitness, adult fitness increased by 0.21 (95% CI 0.14–0.28) units. shows that subjects who were unfit as children had increased odds of obesity and insulin resistance. Similar findings were evident for serum insulin level (data not shown).
Scatter plot of adult fitness level versus child fitness level.
Effect of change in fitness from childhood to adulthood on obesity and insulin resistance in adulthood for all subjects
Fit children were more likely to be fit adults (), and so fitness in childhood has an important indirect effect, mediated by adult fitness. The results also suggested that there were clear disadvantages for subjects who decreased their fitness levels between childhood and adulthood, with this predictor showing even stronger associations with adult outcomes than did degree of child fitness. The estimated coefficients and ORs were similar to those from analyses in which further adjustments for smoking status and alcohol and fat intake in adulthood were made (data not shown).
shows that the proportion of subjects with obesity and the proportion of subjects with insulin resistance were higher in the decreasing-fitness and persistent-low-fitness groups than in the persistent-high-fitness and increasing-fitness groups. Taken together, these findings suggest that confounding by initial child fitness status or BMI does not explain the association of decreasing fitness with higher adult obesity and higher insulin resistance. The principal factor associated with low risk of obesity and insulin resistance in early adulthood is a relatively high level of adulthood fitness. To assess the robustness of these estimates to loss to follow-up, population-weighted analyses of the following variables measured at baseline were implemented: sex, age, socioeconomic status, smoking status, BMI, and relative fitness. The weight for each subject was the inverse of the probability of providing follow-up data given their status on the above factors. The results for the weighted analyses were similar to the nonweighted analyses, suggesting that there is no loss–to–follow-up bias due to lack of representativeness on the variables used to calculate the weights.
Figure 2 Percentage of obese subjects and those with HOMA above the 75th percentile for each of the five fitness-change categories: persistent low fitness (PLF), decreasing fitness (DF), persistent moderate fitness (PMF), increasing fitness (IF), and persistent (more ...)
We restricted the analysis to nonobese children only and again found that lower child fitness (adjusted OR 2.9 [95% CI 1.8–4.8]; P < 0.001) and decreasing fitness (3.9 [2.5–6.1]; P < 0.001) were associated with adult obesity, showing that the findings did not reflect reverse causality.
The association between fitness decrease and insulin resistance persisted after adjustment for both child BMI and waist circumference. Even after accounting for adult obesity, poor child fitness and fitness decrease were associated with a higher risk of insulin resistance, with adjusted ORs of 1.5 (95% CI 1.0–2.3; P = 0.06) and 1.6 (1.1–2.2; P = 0.011), respectively.