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Background: Most identified risk factors for cancer primarily occur in adulthood. As cancers generally have long latency periods, it is possible that risk factors acting earlier in life and accumulation of risks across the life course are important. Thus, focusing only on adult overweight as a modifiable risk factor may overlook childhood as an important aetiologic time window when body size is relevant for future cancer risks. The objective of this study was to review the evidence for associations between birthweight, body mass index (BMI), height and growth from 7-13 years and adult cancer risks based on studies using the Copenhagen School Health Records Register., Methods: The register contains measured anthropometric information on 372,636 children born in 1930-1989. All studies examining associations between early life body size and risks of adult cancer (until 85 years, diagnosed in 1968-2015) were included, comprising 31 studies on 16 different cancer sites. Cancer diagnoses were retrieved via individual-level linkages to the Danish Cancer Registry., Results: Birthweight was differentially associated with bladder, breast, colon, glioma, Hodgkin's disease, liver, kidney (renal cell), melanoma, ovarian, rectal, testicular and thyroid cancer. BMI in childhood was positively associated with risks of bladder (only late childhood), colon, endometrial, kidney, liver, oesophageal (only late childhood), ovarian, pancreatic (<70 years), prostate (only before childhood height adjustment) and thyroid cancer, whereas it was inversely associated with breast cancer. Child height was positively associated with breast, colon, endometrial, glioma, Hodgkin's disease, kidney, melanoma, oesophageal (only women), ovarian, prostate, testicular and thyroid cancer and inversely associated with bladder cancer. Greater than average increases in childhood BMI or linear growth at ages 7-13 increased risks of several cancers., Conclusions: Early life body size and growth are associated with many, but not all adult cancers, suggesting that the aetiology of several cancers may lie earlier in life than previously thought.

Background: Although weight gain in mid- to late adult life is associated with an increased risk of colon cancer, it is unclear if increases or losses in weight from childhood to early adulthood are differentially associated with risks of adult colon cancer., Methods: Weight and height were measured at 7 or 13 years and in early adulthood (17-26 years) in 64,675 boys in the Copenhagen School Health Records Register and the Danish Conscription Database. Cases of colon cancer (n = 751) were identified in the Danish Cancer Registry. Boys and young men were categorized as normal weight or overweight. Associations between changes in weight and colon cancer were examined using Cox proportional hazards regression to estimate hazard ratios (HRs) and 95% confidence intervals (CIs)., Results: Compared with men with a normal weight at 7 years and in early adulthood, men with overweight at both ages had an increased risk of adult colon cancer (HR: 2.73, 95% CI 1.80-4.15). In contrast, men with overweight at 7 years, but not in early adulthood did not have an increased risk of colon cancer (HR: 0.73, 95% CI 0.35-1.54), nor did men with a normal weight at 7 years and overweight in early adulthood (HR: 1.28, 95% CI 0.96-1.70). Similar results were observed for weight status at age 13 years combined with early adulthood., Conclusions: Childhood overweight that persists into early adulthood is associated with an increased risk of colon cancer, whereas overweight that disappears before early adulthood or developed after childhood is not.

Background: Heavy children have an increased risk of being overweight young adults. Whether this risk remains in late adulthood is not well-understood. We investigated body mass index (BMI; kg m(-2)) tracking from childhood to late adulthood., Methods: From the Copenhagen School Health Records Register, 72 959 men and 25 252 women born between 1930 and 1989 with BMI values at 7 and/or 13 years and as adults were included. Using a meta-regression approach, age- and sex-specific partial correlation analyses and logistic regressions were performed., Results: Correlations between BMI at 7 years and young adult ages (18-19 years) were r=0.55 for men and r=0.55 for women. At late ages (60-69 years) these were r=0.28 for men and r=0.26 for women. The correlations did not differ by birth years. Compared with normal-weight 7-year-olds, overweight children had a higher odds of overweight at 18-19 years; odds ratio (OR)=14.02 (95% confidence interval (CI): 12.14-16.19) for men and 10.46 (95% CI: 4.82-22.70) for women. At ages 60-69 years ORs were 5.46 (95% CI: 0.95-31.36) for men and 1.61 (95% CI: 0.83-3.15) for women. Correlations and ORs were stronger at age 13 years than age 7 years as expected, but the overall patterns were similar., Conclusions: BMI tracking was weaker at late adult ages than at young adult ages. Although BMI tracks across the life course, childhood BMI is relatively poor at identifying later adult overweight or obesity at ages when chronic diseases generally emerge.

Background: Weight and weight gain throughout infancy are related to later obesity, but whether the strength of the associations varies during the infancy period is uncertain., Aims: Our aims were to identify the period of infancy when change in body weight has the strongest association with adult body mass index (BMI) and also the extent to which these associations during infancy are mediated through childhood BMI., Methods: The Copenhagen Perinatal Cohort, in which participants were followed from birth through 42 years of age, provided information on weight at 12 months and BMI at 42 years for 1633 individuals. Information on weight at birth, 2 weeks, 1, 2, 3, 4 and 6 months was retrieved from health visitors' records and information on BMI at ages 7 and 13 years from school health records. The associations of infant weight and weight gain standard deviation scores (SDS) with adult BMI-SDS were analyzed using multiple linear regression and path analysis., Results: Higher-weight-SDS at all ages from birth to an age 12 months were associated with higher-BMI-SDS at 42 years (regression coefficients 0.08-0.12). Infant weight gain-SDS was associated with greater BMI-SDS at 42 years only between birth and 3 months (0.09, 95% confidence intervals (CI) 0.04, 0.15) driven by an association between 2 and 3 months (0.12, 95% CI: 0.04, 0.20). The latter was partly mediated through later BMI in the path analysis. Infant weight gain-SDS between 3 and 12 months was not associated with greater BMI-SDS at 42 years., Conclusions: Faster weight gain during only the first 3 months of infancy was associated with increased adult BMI, although not in a consistent monthly pattern. Adult BMI is more sensitive to high weight gain during early infancy than late infancy, but not specifically to the first month of life.