Women who are overweight or obese have up to twice the risk of developing colorectal cancer before age 50 as women who have what is considered a normal body mass index (BMI), according to new research led by Washington University School of Medicine in St. Louis. In the United States, overall rates of new colorectal cancer cases and deaths from the disease have decreased steadily since 1980, largely owing to recommended colonoscopy screening starting at age 50. For reasons that remain unknown, new cases of, and deaths due to, both colon and rectal cancers have been increasing for younger adults ages 20 to 49. The study, published in JAMA Oncology, is among the first epidemiologic analyses of the potential contributors to early-onset colorectal cancer – cases diagnosed under age 50. The researchers found that higher current BMI, BMI at 18 years of age, and weight gain since early adulthood are associated with increased risk of colorectal cancer under age 50. The researchers included collaborators at the Harvard School of Public Health, Brigham and Women’s Hospital, and Massachusetts General Hospital at Harvard Medical School. The study included data from 85,256 women ages 25 to 44 in the Nurses’ Health Study II, which began in 1989. The researchers have collected detailed information on body weight throughout the life course, family and endoscopy histories, and lifestyle factors at study baseline and every two to four years. Up to 2011, doctors diagnosed 114 colorectal cancer cases under age 50.
Compared with women with the lowest BMIs (18.5-22.9 kilograms per square meter), women with the highest BMIs (greater than 30) had almost twice the risk of early-onset colorectal cancer. According to the Centers for Disease Control and Prevention, the normal BMI range is 18.5-24.9 kilograms per square meter. BMIs from 25-29.9 are considered overweight, and BMIs greater than 30 are considered obese. Early-onset colorectal cancer remains relatively rare at about eight cases per 100,000 people, but since these populations do not receive routine screening, cases often are diagnosed at later stages of the disease, making them much more difficult to treat. The researchers estimated that roughly 22 percent of early-onset colorectal cancer could have been prevented had all participants had a normal BMI. On a population scale, this represents thousands of potentially preventable colorectal cancer cases among the younger population. The researchers further found that the higher risk of early-onset colorectal cancer associated with increasing BMI held even among women with no family history of the disease. The American Cancer Society recently lowered the recommended age at which most people should undergo a first screening colonoscopy. The new guidelines recommend screening beginning at age 45, down from the previous recommendation of age 50. More research is needed, including additional validation studies as well as cost-benefit analyses, to see if BMI should be considered in deciding the appropriate age an individual should begin screening or complement current screening efforts.
The study highlight the importance of maintaining a healthy weight, beginning in early adulthood for the prevention of early-onset colorectal cancer. Scientists hypothesized that the obesity epidemic may partially contribute to this national and global concern in early-onset colorectal cancer rates, but they were surprised by the strength of the link and the contribution of obesity and weight change since early adulthood. There are few known risk factors for early-onset colorectal cancer. If the screening age gets pushed before age 50, BMI may be one of the factors to take into account. Yet the cost analysis and risk-benefit analysis for early age of screening remains to be done. The multidisciplinary team has puiblished in another journal another article which describes the association of antibiotic consumption and onset of colon adenomas. They prospectively evaluated the association between antibiotic use at age 20-39 and 40-59 (assessed in 2004) and recent antibiotic use (assessed in 2008) with risk of subsequent colorectal adenoma among 16 642 women aged ≥60 enrolled in the Nurses’ Health Study (NHS) who underwent at least one colonoscopy through 2010. Women who used ≥2 months of antibiotics between age 40 and 59 had a overall risk of 1.69. The associations were similar for low-risk versus high-risk adenomas (size ≥1 cm, or with tubulovillous/villous histology, or ≥3 detected lesions), but appeared modestly stronger for proximal compared with distal adenomas. In contrast, recent antibiotic use within the past four years was not associated with risk of adenoma.
The researchers said more studies are needed to uncover the best ways to identify young people at high risk of colorectal cancer at younger ages. Moreover, the identification of previously “unrelated” factors linked to the condition, will be valuable information for its future preventive picture.
- edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
Liu L et al. Clin Gastroent Hepatol. 2018 Oct; 16:1622-31.
Jeon J et al. Gastroenterology 2018; 154(8):2152-64.
Ding C et al. Onco Targets Ther. 2018; 11:4797-4810.
Cao Y et al., Chan AT. Gut 2018 Apr; 67(4):672-678.