Obese in adolescence, colon cancer in later life? Study doesn't prove cause-and-effect, but suggests the need for healthy habits in childhood. By Steven Reinberg HealthDay Reporter (HealthDay (HealthDay News) -- Obesity and inflammation in late adolescence are associated with increased risk for colon and rectal cancer in adulthood, a new study of Swedish males suggests. The 35-year study found that 16- to 20-year-olds who were obese had more than twice the risk of developing colon or rectal cancer compared to normal-weight teens. And teens with high levels of inflammation had a 63 percent increased risk of developing colorectal cancer, compared with those with low levels of inflammation, researchers found. "These results are important because we know relatively little about the role of early life exposures in the development of colon cancer," said lead researcher Elizabeth Kantor, a postdoctoral research fellow in the department of epidemiology at the Harvard School of Public Health in Boston. However, Kantor said this study doesn't prove that obesity and inflammation in adolescence caused the increased risk for colorectal cancer. "We are talking about associations and cannot say whether or not they are causal," she said. "For this reason, I think it's important to be cautious with the conclusions of the study," she added. For one thing, nothing was known about the diets of the boys studied, the researchers noted. Obesity is thought to be a cause of inflammation, which has been associated with an increased risk for a variety of cancers, according to the American Cancer Society. The study findings were scheduled for presentation Monday at a meeting of the American Association for Cancer Research in New Orleans. Dr. Andrew Chan, an associate professor in the department of medicine at Harvard Medical School, said there is "pervasive evidence" that obesity is a risk factor for colon cancer. It isn't clear, however, when obesity matters the most, he said. "We know that the development of colon cancer takes many years. So it is important to understand whether it's obesity earlier or later in life that is more influential," Chan said. Kantor agreed that more work is needed to determine how obesity and inflammation might influence colorectal cancer risk at different stages in life. For the study, Kantor's team analyzed data on nearly 240,000 Swedish males drafted into the military from 1969 to 1976 when they were between 16 and 20 years of age. When they were inducted into the military, the men underwent a blood test to measure inflammation in their body and had their height and weight recorded. To identify men with colorectal cancer from this group, the researchers linked draft records with a national cancer registry. By the start of 2010, the investigators found that 501 men had developed colon cancer and 384 had developed rectal cancer. Obesity was associated with 2.37 times greater risk of developing colorectal cancer, the researchers said. Dr. David Katz, director of the Yale University Prevention Research Center, wasn't surprised by the findings. "We have long known that obesity is associated with an increased risk of almost all cancers, and obesity is associated with inflammation," he said. Establishing healthful eating and physical activity patterns in childhood is crucial, he said. "A healthy lifestyle is the best defense we have against obesity, inflammation, and the dangers these portend over a lifetime," he said. Data and conclusions presented at meetings are typically considered preliminary until published in a peer-reviewed medical journal. Dr. U.S. National Cancer Institute. SOURCES: Elizabeth Kantor, Ph.D., postdoctoral research fellow, department of epidemiology, Harvard School of Public Health, Boston; David Katz, M.D., M.P.H., director, Yale University Prevention Research Center, New Haven, Conn.; Andrew Chan, M.D., M.P.H., associate professor, department of medicine, Harvard Medical School, Boston; Sept. 29, 2014, presentation, American Association for Cancer .