Overweight boys at greater risk of colon cancer as adults, but losing weight may modify risk

New research presented at this year's European Congress on Obesity (ECO) in Porto, Portugal (17-20 May) suggests that overweight boys may be at greater risk of colon (bowel) cancer when they grow up than their slimmer friends. However, overweight boys who shed the pounds and achieve a healthy weight by young adulthood do not appear to be at increased risk of colon cancer as adults. The findings underline how important it is for children to be a healthy weight.

Colon cancer is the 4th most common cancer in adults, with around 41,000 cases diagnosed each year in the UK. Previous research shows that overweight children are at higher risk of colon cancer as adults, but it is unclear whether changes in body mass index (BMI) between childhood and young adulthood alter this risk.

In this study, Dr Britt Wang Jensen and Associate Professor Jennifer Baker from Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark and colleagues analysed the health records of over 61,000 Danish school boys born between 1939 and 1959, to examine how changes in BMI in childhood and young adulthood are associated with colon cancer risk in adulthood. Participants' weight and height were measured at age 7 years and in young adulthood (age 17-26 years) and BMI was calculated. These young men were then linked with the Danish Cancer Register and followed from the age of 40 years to identify cases of colon cancer.

During an average (median) 25-year follow-up, more than 700 boys went on to develop colon cancer. Analyses showed that boys who were overweight (BMI greater than 17.88 kg/m2) at age 7 years but normal weight (BMI under 25.0 kg/m2) as young men had similar risk of adult colon cancer as those who maintained a stable, healthy weight throughout. In contrast, overweight boys who remained overweight as young men had twice the colon cancer risk. The study took educational level into account but not lifestyle factors that might contribute to a person's risk of developing cancer.

The authors conclude: "Overweight boys that lose weight and achieve a normal-weight status by young adulthood do not carry an increased risk of adult colon cancer compared with boys who remain normal-weight as young men. However, overweight boys who remain overweight as young men have an increased risk of adult colon cancer. These results highlight the importance of weight management in childhood."

They add: "Our next steps are to expand our focus and examine other forms of cancer along with other non-communicable diseases to create a full picture of how a man's weight development across his life, even from birth, is associated with his risk of disease."