BACKGROUND & AIMS: Childhood overweight increases the risk of early development of non-alcoholic fatty liver disease, which may predispose to carcinogenesis. We investigated if childhood body size during school ages was associated with the risk of primary liver cancer in adults.

METHODS: A cohort of 285,884 boys and girls, born 1930 through 1980, who attended school in Copenhagen, were followed from 1977 to 31 December 2010. Their heights and weights were measured by school doctors or nurses at ages 7 through 13 years. Body mass index (BMI) z-scores were calculated from an internal age- and sex-specific reference. Information on liver cancer was obtained from the National Cancer Registry. Hazard ratios and 95% confidence intervals (95% CI) of liver cancer were estimated by Cox regression.

RESULTS: During 6,963,105 person-years of follow-up, 438 cases of primary liver cancer were recorded. The hazard ratio (95% CI) of adult liver cancer was 1.20 (1.07-1.33) and 1.30 (1.16-1.46) per 1-unit BMI z-score at 7 years and 13 years of age, respectively. Similar associations were found in boys and girls, for hepatocellular carcinoma only, across years of birth, and after accounting for diagnoses of viral hepatitis, alcohol-related disorders, and biliary cirrhosis.

CONCLUSIONS: Higher BMI in childhood increases the risk of primary liver cancer in adults. In view of the high case fatality of primary liver cancer, this result adds to the future negative health outcomes of the epidemic of childhood overweight, reinforcing the need for its prevention.