New research being presented at this year's European Congress on Obesity (ECO) in Vienna, Austria (23-26 May) suggests that being overweight in childhood coupled with excessive weight gain during puberty may contribute to the development of adult colon cancer in men. However, overweight boys who do not have above average weight gain during puberty do not appear to be at increased risk of colon cancer as adults.
The findings come at a time of climbing childhood obesity rates, with one in three American children and teenagers, and more than one in three UK primary schoolchildren (ages 10-11), considered overweight or obese.
Colorectal cancer is the third most common cancer in adults worldwide, with around 41,000 cases of colon (bowel) cancer diagnosed each year in the UK, and 97,000 in the USA. Previous studies have shown that boys who are overweight as children are more likely to develop colon cancer as adults, but the influence of childhood body mass index (BMI) independent of BMI change during puberty on colon cancer risk is not known.
To provide more clarity, Dr Jimmy Celind from the University of Gothenburg in Sweden analysed data on 37,663 Swedish boys born between 1945 and 1961 who had BMI measured in both childhood (8 years) and young adulthood (20 years). Pubertal BMI change was calculated as BMI at age 20 minus BMI at age 8. Participants were categorised by BMI in childhood (cutoff for childhood overweight 17.9 kg/m2) and pubertal change in BMI which was below and above the median (average) in the study population. Participants were linked with national registers and followed until December 2013 to identify cases of colon cancer.
During an average of 37.7 years follow-up, 257 new cases of colon cancer and 159 cases of rectal cancer were identified. The researchers controlled for factors such as country of birth, birth year, birthweight, childhood height and, young adult BMI.
When analysed alone, childhood BMI at 8 years was associated with risk of a colon cancer diagnosis in adulthood, but BMI change during puberty in itself was not linked with colon cancer risk.
The researchers then analysed the joint effect of childhood BMI and BMI change during puberty. Interestingly, boys who were overweight or obese at age 8 years but had a lower than average BMI change during puberty were not at increased risk of adult colon cancer. In contrast, overweight or obese boys (at 8 years of age) with a higher than average BMI change during puberty had a 48% higher risk of developing colon cancer in adulthood compared to their slimmer counterparts (1.6% overweight child participants with a higher than average pubertal BMI change increase vs 0.7% participants who were normal weight at 8 and 20 years of age).
Neither overweight in childhood or a high BMI change during puberty were associated with an elevated risk of rectal cancer.
The authors acknowledge that their findings show observational differences rather than evidence of cause and effect. They conclude: "Our results show that BMI throughout childhood and adolescence may play a role in the risk of colon cancer in later life. Specifically, men who are overweight or obese as boys with above average weight gain during puberty are at higher risk of developing colon cancer. More research is needed to discover whether losing weight in adulthood could lower the risk."
The authors note some limitations, including that the study included mainly Caucasian men, so the findings cannot be generalised to all ethnic groups in other countries. They also note that adjustment for BMI at an older adult age, physical exercise, and a high caloric/low fibre diet was not possible. Lastly, as Sweden did not have mandatory female military conscription at the time, they were unable to retrieve young adult BMI for women, so it was not possible to determine sex-based differences in the association between BMI change during puberty and adult risk of colon cancer.