Obese male teens were more than twice as likely to develop colorectal cancer later in life than normal-weight peers.
Colorectal cancer, also known as bowel cancer, is the third most common cancer in both men and women in the US, with more than 93,000 cases of colon cancer and almost 40,000 cases of colorectal cancer expected to be diagnosed this year.
According to the research team, past studies have associated obesity and systemic inflammation in adults with increased risk of colorectal cancer. They note, however, that few studies have investigated how such conditions during adolescence affect later-life risk of the disease.
As such, the team monitored the health of 239,658 men who underwent a health assessment during enlistment for the Swedish military between 1969 and 1976, when they were aged 16-20 years.
During this assessment, the men's weight and height were checked, as well as their erythrocyte sedimentation rate (ESR) - a measure of inflammation in the body, as determined by the rate of fall in red blood cells (erythrocytes).
Using national cancer registry data, the researchers monitored incidence of colorectal cancer among the men up until 2010.
Obesity in late adolescence poses 2.38 times greater risk of later-life colorectal cancer
At time of enlistment, almost 12% of the men were underweight, 81% were normal weight, 5% were moderately overweight, 1.5% were very overweight and 1% were obese.
During the average 35-year tracking period, 885 of the men developed colorectal cancer. Of these cases, 384 were rectal cancers.
The results of the study revealed that men who were very overweight at time of enlistment - defined as having a body mass index (BMI) of 27.5-30 kg/m2 - were twice as likely to develop colorectal cancer during middle age than those who were a normal weight at enlistment (BMI of 18.5-25 kg/m2).
Men who were obese at the time of enlistment - a BMI of greater than 30 kg/m2 - were 2.38 times more likely to develop colorectal cancer in later life than those of a normal weight, according to the results.
What is more, the researchers found that men with a high ESR - greater than 15 mm/hour - who had no known inflammatory bowel disease at time of enlistment were found to be at 63% higher risk of developing colorectal cancer during middle age than those with a low ESR - less than 10 mm/hour.
The team points out that the effects of BMI and inflammation on later-life colorectal cancer were independent of each other, suggesting both contribute to this risk via different mechanisms.
Commenting on their findings, the researchers say:
"Our study suggests a graded association between adolescent inflammation, as measured by ESR, and CRC [colorectal cancer], and an even stronger association between adolescent BMI and CRC risk. These results suggest that BMI and inflammation, as measured by ESR, in early life may be important to the development of CRC."
The researchers are unclear as to what drives the link between adolescent BMI and inflammation and later-life colorectal cancer link, but they stress that this is something that should be investigated in future research.
"With additional follow-up, and therefore statistical power, future studies may address how adolescent inflammation and BMI interact to affect CRC risk, and further work may seek to address how these factors, independently and jointly, relate to CRC mortality," they add.
The team admits there are some limitations to their study. For example, they were unable to determine men's BMI and inflammation status later in life. As such, the findings could reflect the known link between adult obesity and inflammation and increased risk of colorectal cancer.
"We are therefore unable to comment on whether the strong association between adolescent BMI and CRC could be mitigated by weight loss during adulthood," they note.
In addition, they say their results should not be generalized to women, particularly since past studies have suggested a weaker link between adult BMI and inflammation and risk of colorectal cancer among this population.
A report conducted by Cancer Research UK in March revealed that women who are obese are 40% more likely to develop certain forms of cancer in their lifetime than those of a healthy weight, including pancreas cancer, colorectal cancer, kidney cancer, breast cancer and esophageal cancer.