Of 1142 children in the original cohort, 932 were followed up to the end of the first year. Forty seven of these participants died after the age of 18 years. At age 50 years, 412 participants (44%) attended for clinical examination and blood sampling. A total of 688 and 628 participants were measured at age 9 and 13 years, respectively. Heights and weights at age 50 were available for 529 subjects: 409 measured and a further 120 self reported in the postal questionnaire.
Participants who were followed up as adults were slightly less socioeconomically deprived than those not followed up but were no more likely to have been overweight or underweight in childhood. Birth weights were similar among the two groups.
During childhood, height progressively dropped away from contemporary norms, with a striking inverse social class gradient that narrowed in adulthood (table ). In contrast, there was no social class gradient for body mass index in childhood, although there was a tendency for the children in the lowest social class to be thinner. Body mass index rose substantially through puberty and adulthood, and by the age of 50, 140 (60%) men and 120 (41%) women were overweight (body mass index>24), of whom 91 (17% of both sexes) were obese (body mass index>30). Those in the lower social classes at birth had significantly higher body mass index and percentage body fat at 50, whereas adult social class showed only a weak association with adult obesity.
Mean (SD) height and body mass index standard deviation scores from childhood to adulthood by father's social class at birth
Relation between childhood and adult obesity
Body mass index in childhood showed a moderate, significant correlation with adult body mass index (age 9: r=0.24, P<0.001; age 13: r=0.39, P<0.001). At age 50, those who had been above the 90th centile for body mass index at age 9 or 13 years were between five and nine times more likely to be obese (body mass index >30) than those in the thinnest quarter in childhood (table ). The association between body mass index in childhood and adult percentage body fat was weaker than that with adult body mass index (age 9: r=0.1, P=0.07; age 13: r=0.22, P<0.001). Little tracking was seen between any level of body mass index at age 9 and adult percentage body fat. Children in the top tenth of body mass index at age 13 were twice as likely as the remainder to be in the top quarter for adult percentage body fat, but children in the bottom quarter were equally likely to have either high or low body fat as adults. Most of those in the top quarter for body fat aged 50 had not been overweight as children: 94% had been below the 90th percentile for body mass index at age 9 and 79% at age 13.
Proportions of children underweight or overweight at ages 9 or 13 years who were overweight or obese at age 50
Although adult percentage body fat was strongly correlated with adult body mass index (r= 0.63, P <0.01), for every level of adult body mass index the leanest children had significantly higher adult percentage body fat (linear regression: body fat (%)=5.4×body mass index aged 50–1.1×body mass index aged 9+32.5).
Relation between childhood obesity and adult risk factors
In univariate analysis, body mass index and percentage body fat aged 50 were both strongly associated with most risk factors for adult disease (table ). Body mass index at age 9 and 13 showed weak (mainly inverse associations with risk factors, although the only significant associations were between body mass index age 9 and total cholesterol and triglyceride concentrations in women. After adult body mass index was adjusted for, childhood body mass index showed consistent inverse associations with risk of adult disease. In women, associations with body mass index age 9 were significant for triglycerides, fasting insulin, 2 hour glucose, systolic and diastolic blood pressure, and total cholesterol, and associations with body mass index at age 13 were significant for triglyceride, fasting insulin, and 2 hour glucose concentrations. In men, there were significant associations between body mass index at age 9 and triglyceride, fasting insulin, and 2 hour glucose concentrations and between body mass index at age 13 and fasting insulin concentration (table ).
Association between risk factors age 50 with body mass index at ages 9, 13, and 50 years and percentage body fat (values are standardised regression coefficients)
Association between body mass index at ages 9 and 13 years in childhood and risk factors age 50, adjusted for body mass index age 50 (values are standardised regression coefficients)
When we adjusted for adult percentage body fat rather than body mass index, the striking relations between childhood body mass index and fasting insulin and 2 hour glucose concentrations were much attenuated in women and largely disappeared in men (table ). Similarly, the association between childhood body mass index and adult blood pressure largely disappeared.
Association between body mass index at age 9 and 13 years and risk factors at age 50, adjusted for percentage body fat age 50 (values are standardised regression coefficients)
For women, the association between body mass index aged 9 and cholesterol and triglyceride concentrations remained significant, with those women thinnest at age 9 having higher concentrations for every stratum of adult fatness. The non-significant correlations between childhood body mass index and adult risk factors were still consistently inverse for both sexes and ages. Including social class at birth, height, or weight in childhood made little difference to these results.
The 47 subjects who had died in adulthood and the 20 subjects who met the full criteria for the metabolic syndrome were no more likely to have been in the top quartile for body mass index at ages 9 or 13 years than the others.