Adult obesity and inflammation have been associated with an increased risk of bowel cancer, which is the third most common form of cancer among men, worldwide. However, less is known about how obesity and systemic inflammation might be influential during late adolescence.

The researchers therefore tracked the health of almost 240,000 Swedish men, who had been conscripted into the military between the ages of 16 and 20 in 1969-76.

At enlistment, the men had a health check, which included weight and height, and ESR levels. The men were then monitored for bowel cancer up to 2010, using national cancer registry data.

At the time of conscription, nearly 12% of the men were underweight, while almost 81% were of normal weight. Some 5% were moderately overweight; 1.5% were very overweight; and 1% were obese.

During the monitoring period, which spanned an average of 35 years, 885 of the men developed bowel cancer, 384 of which were rectal cancers. Compared with those whose weight was within the normal range when they enlisted (BMI 18.5-25 kg/m2), those who were very overweight, with a BMI ranging between 27.5 and nudging 30, were twice as likely to develop bowel cancer.

Obesity in young adulthood, classified as a BMI of more than 30, was associated with a 2.38 higher risk of developing bowel cancer.