Obese Teenagers Have Twofold Higher Risk for Colorectal Cancer

Susan London

May 26, 2015

Male teenagers who carry a lot of excess weight are more than twice as likely to develop colorectal cancer (CRC) by middle age, according to a large cohort study. Those with a high level of systemic inflammation are also at increased risk.

The study, published online May 26 in Gut, is noteworthy as one of the few to evaluate the association between teenage body mass index (BMI) and bowel cancer in adulthood. It is also the first to evaluate the association of teenage systemic inflammation, assessed here with erythrocyte sedimentation rate (ESR), with this outcome, according to the authors.

"These results suggest that BMI and inflammation, as measured by ESR, in early life may be important to the development of CRC," write Elizabeth D. Kantor, PhD, from the Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts, and colleagues. "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. "Further research is needed to better disentangle BMI and inflammation from associated exposures, and similarly, from exposure at other points in the life course."

The investigators analyzed data on BMI and ESR among 239,658 Swedish men who had compulsory military enlistment examinations at 16 to 20 years of age; those with a history of inflammatory bowel disease were excluded. National cancer registry data showed that the cohort had 885 cases of CRC (501 colon and 384 rectal) during a mean follow-up of 35 years.

In multivariate analyses, teenagers who had a BMI in an upper overweight category (BMI, 27.5 to <30 kg/m2) had a 2.08-fold (95% confidence interval [CI], 1.40 - 3.07) higher risk of developing CRC relative to teenagers who had a normal weight (BMI, 18.5 to <25 kg/m2). Those who were obese (BMI, ≥30 kg/m2) had a 2.38-fold (95% CI, 1.51 - 3.76) higher risk. There was a graded relationship whereby risk increased significantly across the five BMI categories studied. In site-specific analyses, findings were similar for colon cancer and for rectal cancer individually.

The researchers also found that teens with a high ESR (≥15 mm/hour) had a 1.63-fold (95% CI, 1.08 - 2.45) higher risk for CRC in adulthood relative to peers with a normal ESR (<10 mm/hour). Again, there was a graded relationship, whereby risk increased significantly across the three ESR categories studied. However, in site-specific analyses, the association was significant only for colon cancer, and the overall findings were attenuated somewhat after exclusion of teenagers having an illness at the time of enlistment examination.

"[T]he strong association observed between adolescent obesity and early-to-mid-life CRC, coupled with the increasing prevalence of adolescent obesity...may shed light on the increase in CRC incidence among young adults in the USA," the investigators speculate.

Given that the association of BMI with CRC risk was independent of ESR, it may instead be mediated by factors such as insulin, leptin, or steroid hormones, they propose. "However, it is also possible that adolescent BMI may affect CRC through an inflammatory pathway not reflected by ESR," they add.

Dr Kantor is supported by the National Cancer Institute and the Rose Traveling Fellowship from the Harvard School of Public Health. Two coauthors are supported by Örebro University Strategic Funding, and the cohort was developed with support from the UK Economic and Social Research Council as grants to the International Centre for Life Course Studies. The other authors have disclosed no relevant financial relationships.

Gut. Published online May 26, 2015. Abstract

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