Bowel cancer is the third most common cancer among men worldwide, with nearly 1.4 million new diagnoses each year. Links with obesity in adulthood are fairly well established with what appears to be a rise in risk with increasing body mass index. The link is significantly stronger for men than it is for women. Much less is known about potential causes at earlier stages of life, especially adolescence, as Professor Scott Montgomery from UCL explains.
Adolescence marks the transition from childhood to adulthood and is a period of accelerated growth, especially for men. We wanted to look at whether obesity, or even just excess weight, during the teenage years increase the likelihood of colorectal cancer later in life?
Asking men diagnosed with bowel cancer what they weighed as teenagers is not a reliable source of data. What we needed to examine this question robustly was a large sample of men who were accurately measured in their youth and are now sufficiently old for a significant number to have developed bowel cancer.
One such group is men who experienced compulsory Swedish military conscription assessments. Around a quarter of a million young men aged around 18 years were assessed for conscription between 1969 and 1976. After excluding those with errors in the original measurements and excluding men with pre-existing medical conditions gave us a sample of just under 240,000 – equivalent to 8 and half million person years of data.
The men’s height and weight was measured by trained personnel during the conscription examination. From these data body mass index (BMI) or kg/m² was calculated and those numbers were put into five groups – underweight (BMI of less than 18.5), normal (BMI of 18.5 to 24.9), lower overweight (BMI of 25 to 27.4), upper overweight (BMI of 27.5 to 29.9) and obese (BMI of over 30).
A blood test was also taken and tested for signs of higher levels of inflammation, which can signal diseases processes relevant to bowel cancer risk.
Over an average of 35 years following conscription, 885 of the men were diagnosed with bowel cancer, comprising 501 cases of colon cancer and 384 cases of rectal cancer.
Men who had been underweight in adolescence had a slightly lower risk of a colorectal cancer diagnosis than normal weight men. Lower overweight men had a non-statistically significant higher risk, upper overweight men had a statistically significant 2.08-fold higher risk and obese men had a 2.38-fold higher risk.
Men, who had suffered high levels of late adolescent inflammation, were found to be at a 63% higher risk of being diagnosed with bowel cancer than those with normal levels. The link between BMI and a diagnosis was independent of inflammation levels, suggesting adolescent BMI may be operating in a different way and through mechanisms other than the inflammation detected during adolescence.
The average age at the end of follow-up was 53.9 years, so our analysis did not look at any changes in late adulthood. It seems unlikely, though, that the upper weight groups would suffer less in later years.
It was also impossible to account for whole life measures of BMI and inflammation and so we are not able to comment on whether the strong association between adolescent BMI and bowel cancer could be mitigated by weight loss during adulthood. It is, however, plausible that it is the total duration of exposure to high BMI or inflammation that brings the increased risk rather than exposure at a specific age. High BMI or inflammatory processes already present during adolescence may persist for many years into adulthood.
It is also important to stress that the findings do not necessarily apply equally to women. Certainly, other studies have shown the associations between BMI and inflammation and bowel cancer are weaker among women than men.
All that said, this is a robust, important study based on good quality measurement and a lengthy time frame. At a time when increasing adolescent obesity in the United States, for instance, appears to be being followed by an increasing incidence of bowel cancer among young adults, it contributes to the case for further work to be undertaken with some urgency.
What our research does suggest is a graded association between adolescent inflammation and bowel cancer and an even stronger association between adolescent BMI and the risk of bowel cancer in men. We have notable evidence of a link between these exposures at a particularly vulnerable stage of development and the later incidence of bowel cancer.
More work needs to be done, particularly to clarify how inflammation and BMI act or interact to affect an increased risk of bowel cancer. Further research is also needed to disentangle these factors from other risks both in adolescence and later life.
Adolescent body mass index and erythrocyte sedimentation rate in relation to colorectal cancer risk is research by Elizabeth D Kantor, Ruzan Udumayan, Lisa B Signorello, Edward L Giovannucci, Scott Montgomery and Katja Fall and is published in the journal, Gut.
Photo credit: Marina Lobanova