Adolescent Obesity and Inflammation in Relation to Colorectal Cancer Risk: Recent Findings and Future Implications.

[Author Affiliation]Elizabeth D. Kantor. 1 Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, MA.Edward Giovannucci. 1 Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, MA. 2 Department of Nutrition, Harvard T. H. Chan School of Public Health, Boston, MA. 3 Channing Division of Network Medicine, Brigham and Women's Hospital, Boston, MA.-Jamie Devereaux, Features EditorChildhood Obesity: Is the connection between higher body mass index (BMI) and colorectal cancer risk in adults solidly defined at this point?Dr. Kantor: The positive association between BMI in adulthood and risk of colorectal cancer is fairly consistent in the literature. Interestingly, the association between adult obesity and colorectal cancer seems to be stronger among men than women. While this could be due to differences in hormones, the underlying reasons for this pattern of association are not entirely clear.Dr. Giovannucci: In adults, there have been many studies on adult BMI and risk of colorectal cancer--I believe there are well over 50 studies now. These studies have been summarized in meta-analyses, and these meta-analyses indicate a positive association between adult BMI and risk of colorectal cancer. There are some that show the association is stronger in men. But it is there for women, too.In several studies, the association is stronger in premenopausal women, and then it weakens a bit in postmenopausal women, and we do not know why that is. But as Dr. Kantor suggested, it might be related to hormones. For example, in postmenopausal women, obesity is associated with higher estrogen levels, and there is some evidence that estrogens may be protective against colon cancer, so the women may be getting some benefit from the estrogens.CO: You were both on the author team of a recently published study1 looking at BMI and adolescents' colorectal cancer risk (CRC). Could you discuss why you decided to take on this missing component in current literature?Dr. Kantor: While we know a lot about adult obesity and colorectal cancer, we know less about the association between adolescent obesity and the risk of colorectal cancer.With colleagues in Sweden, we were able to use existing Swedish registry data to evaluate the association between measured adolescent BMI and risk of CRC in a large cohort of men conscribed in the Swedish military between 1969 and 1976.The fact that BMI was measured in this study is important because recall of adolescent BMI is imperfect, and any degree of error can diminish our ability to see associations.More importantly, since we had such a large cohort study, with almost 240,000 men, we were able to disaggregate adolescent obesity from adolescent overweight, and were able to further break up the overweight group into two groups, lower overweight and upper overweight. In a smaller study, we couldn't have done that, because in the '60s and '70s, we did not have nearly as many overweight and obese adolescents as we have today.CO: Did the large data set on adolescent males guide your choice for an all-male cohort or might you have focused on this group regardless given what you know about the association in adult men?Dr. Kantor: We were able to examine the association between adolescent obesity and risk of colorectal cancer because adolescent height and weight were collected on men conscribed in the Swedish military, and this information was recorded in the national conscription registry. As conscription was mandatory for men at this time in Sweden, we had data on adolescent BMI for almost the entire male adolescent population, which is wonderful. However, we did not have data on women and were therefore unable to include them in the study. In the ideal world, we would do this study among women, as well.CO: Could you discuss how strong you felt the link was between BMI and colorectal cancer risk in your findings? …