Girls who are overweight as young children and teens may face an increased risk for colorectal cancer decades later, regardless of what they weigh as adults, suggests a new study.
The study, published in Cancer Epidemiology Biomarkers and Prevention, is partially funded by the American Institute for Cancer Research.
“Our study supports the growing evidence that early-life body size can influence risk of colorectal cancer many decades later,” said senior study author Esther K. Wei, ScD, currently at the California Pacific Medical Center. “Although we don’t need any additional evidence to encourage obesity prevention and increased physical activity in children, this study adds additional imperative to prioritizing children’s health.”
What population did the study examine, and what factors were accounted for?
For the study, researchers pulled data from two large and long-term cohorts: One included 75,238 women who were part of the Nurses’ Health Study; the other included 34,533 men from the Health Professionals Follow-up study. In 1988, participants were presented with a set of nine diagrams of body shapes, ranging from the most slender to the most overweight. Participants selected what his or her body shape looked like at ages 5, 10, 20, 30, and 40, along with their current age. Then everyone regularly answered questionnaires about their weight, activity, diet and other lifestyle habits.
What did the study find?
During an average of 22 years, 2,100 people had developed colorectal cancer. After adjusting for adult weight, the researchers found that women who were overweight as young children had a 28 percent higher risk of colorectal cancer compared to those who were most lean at those ages. Women who were overweight as adolescents had a 27 percent increased risk.
Unexpectedly, the same link for overweight boys and adult colorectal cancer was not found.
Not seeing the similar link among men could be due to faulty recall, chance, or unknown biology, says Wei. “We really don’t know why we only observed the associated in women and not in men, but since this is still a relatively new area of research, it’s too early to conclude that this association does not exist in men.”
What should we want to see in future studies?
Future studies investigating molecular subtypes of colorectal cancer would also help to better understand the potential mechanisms, because colorectal cancer is a group of heterogenous disease, adds Xuehong Zhang, study author and instructor at Harvard Medical School.
Disentangling the independent link between being overweight as a youth and as an adult is challenging, note the authors.
What can excess weight mean for adults?
For adults, there is a clear link between being obese and increased risk of colorectal cancer – for both women and men – as well as many other cancers. Excess body fat can cause high levels of insulin and insulin-like hormones, which may fuel colorectal cancer.
The role of excess body fat and cancer risk over the life-course is an emerging and important area of research. Approximately one-third of children and adolescents are overweight or obese, according to the Centers for Disease Control and Prevention.
“We already know that overweight kids often become overweight adults. And overweight adults are at risk for many cancers,” says Alice G. Bender, MS, RDN, AICR’s associate director for nutrition programs. “This study emphasizes how important it is for parents and caregivers to help kids choose healthy habits – so it becomes natural for them. Letting your kids see you enjoy colorful fruits and vegetables, giving them healthy options, and taking fun 5-minute activity breaks are just a few of the ways you can set your kids on a path to be healthy throughout life.” Check out the Activate Your Summer Shield program’s activities and recipes for more fun ways to get your kids eating healthier and moving more. Then see our 10 Intuitive Eating Tips for Your Teen.
The study was supported by the American Institute for Cancer Research with a grant to Dr. Kana Wu and grants from the National Institutes of Health.
Notes for Health Educators
- For childhood weight, study authors used the average of pictorial image analysis at ages 5 and 10; for adolescent weight, authors used the average at ages 10 and 20. Adult women were asked to recall their body size at those young ages.
- Body shape for categorizing overweight was level 5 and higher, compared to the most lean body shape of level 1.
- AICR’s most recent Colorectal Cancer CUP report found that risk increases with obesity, alcohol, and high amounts of red and processed meats; risk decreases with physical activity and foods containing fiber.
- AICR now links overweight and obesity to ten cancers, they are: liver, ovarian, colorectal, post-menopausal breast, advanced prostate, endometrial, esophageal, kidney, pancreatic and gallbladder. Our infographic is here.
- The research was initiated when Dr. Esther Wei was at the Channing Division of Network Medicine, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School.