Adult obesity is a well-established risk factor for colorectal cancer. However, to date few studies have examined the possible association of colorectal cancer with childhood obesity. It is therefore not clear if the association is due to development of obesity in adult life or may be influenced by body size already from childhood. In this population-based study, the authors analysed if childhood body mass index (BMI: kg/m2) (age 7 to 13 years) is associated with the risk of colon and rectal cancer in adulthood.
The researchers used the Copenhagen School Health Records Register to identify children who were born from 1930–1972 and had information on height and weight from their school health examinations. BMI was transformed into z-scores, which is a method for comparing a child’s BMI to a reference population. Cases were identified by linkage to the Danish Cancer Registry.
The team found that among 257,623 individuals (49.7% women), 2,676 were diagnosed with colon cancer (47.5% women) and 1,681 with rectal cancer (38.9% women). For each z-score unit increase in BMI at age 13 years, there was a 9% increased risk of developing colon cancer in adulthood. To put this in perspective, compared to an average height and weight boy born in the late 1950s with a BMI of 17.8 kg/m2 (154.5 cm, 42.5 kg) another boy with a similar height but who weighed 5.9 kg more would have a 9% higher risk of colon cancer. Results were essentially similar at all other ages (7 to 12 years).
The results were mainly driven by the association observed between BMI and cancers of the sigmoid colon (1182 cases), each increase in BMI z-score at age 13 years increased the risk of that cancer by 11%. Associations between BMI and rectal cancer were generally not significant.
The authors conclude: “BMI in childhood was associated with the later risk of colon cancer, whereas there were limited indications of associations with rectal cancer. These findings suggest that BMI in childhood may influence the risk of colon but not rectal cancer in adulthood.”
They say their study further emphasises the importance of maintaining a healthy weight in childhood.
And they add: “Since no information is available on adult BMI in the present study we cannot rule out that the results observed are due to continuation of large body size from childhood to adulthood. However, if this was the case we would expect to see an increasing risk of colon cancer with increasing age in childhood, which is not the case. It is possible that exposure to excess weight already from childhood increases the risk of colon cancer.”