Compared to women with a healthy BMI, obese women have up to twice the risk of developing colorectal cancer—these are the results of a new Washington University School of Medicine study published in JAMA Oncology.
Overall, rates of new colorectal cancer cases and deaths have decreased in the United States since 1980, largely due to recommended screening starting at age 50. However, new cases and deaths of colon and rectal cancers have been increasing in younger adults between the ages of 20 and 49.
The researchers in the current study suspected that obesity was a contributing factor in this increase, but they were surprised by just how strong a correlation their results returned.
The study included data from 85,256 women ages 25 to 44 that were part of the Nurses’ Healthy Study II, which began in 1989. Data on weight, lifestyle factors, and endoscopy histories was collected every two to four years from the participants in this study. During that time 114 colorectal cancer cases occurred in women under 50.
Compared with women with the lowest BMIs (18.5-22.9), women with the highest BMIs (higher than 30) had almost twice the risk of developing early-onset colorectal cancer. In addition to current BMI, BMI at 18 years of age, and weight gain since early adulthood were found to be associated with increased colorectal cancer risk. The researchers estimate that roughly 22% of early-onset colorectal cancer could have been prevented if the participants had a BMI of 18.5-24.9, which is considered the healthy range for BMI.
One limitation of this study is that it only established an association between early-onset colorectal cancer and obesity. More data is needed to conclude that this is not the result of confounding factors. Nevertheless, the current findings warrant further study and could potentially change the screening recommendations for those in high-risk groups.