A Danish study has shown that adults who were overweight as children have an increased risk of developing colon cancer, but not rectal cancer. However, losing weight can prevent this. Similarly, overweight young adults have a lower risk of developing colon cancer if they were not overweight in childhood. A researcher says that early intervention on obesity can also save society money.
Researchers have long known that obesity in adults is linked with an increased risk of developing various types of cancer, including colon cancer. A Danish study shows that this risk also applies to childhood obesity, and not just to adults. People who were overweight as children have a greater risk of developing colon cancer in adulthood. Childhood obesity is also correlated with an increased risk of developing colon cancer: the higher the body mass index (BMI), the greater the risk. The study also shows that boys and girls do not differ in how overweight increases risk of developing colon cancer.
“This is not a dramatic increase in the risk of developing colon cancer, and people do not definitely develop colon cancer just because they were overweight as children. However, we found a statistically significant increased risk of about 20%,” explains a researcher behind the study, Thorkild I.A. Sørensen, Professor, Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen.
The study has been published in the European Journal of Epidemiology.
Study includes 260,000 Danish children
In the study, the researchers compared BMI data from school records for children born in 1930–1972 with the incidence of colon and rectal cancer from the Danish patient registries. The study included 260,000 Danes, of whom 2676 developed colon cancer and 1681 rectal cancer as adults.
When the researchers compared the study group’s data on BMI as children with the risk of developing these two types of cancer, they discovered that the adults who were overweight as children had a greater risk of developing colon cancer, but not rectal cancer. The increase in risk was about 20%, and this should be compared with the fact that about 1 in 1000 adults in the study group developed colon cancer.
“Researchers have long known that obesity in adults increases the risk of colon cancer, but the new aspect of this study is that childhood obesity also increases the risk,” says Thorkild I.A. Sørensen.
Unknown reasons for link between obesity and colon cancer
Researchers do not know how obesity is causally linked to the development of colon cancer, but Thorkild I.A. Sørensen speculates that obesity results in metabolic changes that may affect cells in the colon. This may involve hormonal changes that increase the risk of cancer-promoting mutations. More specifically, these hormonal changes may affect the mucosal barrier of the colon. This theory could also explain the differences in the risk of developing colon versus rectal cancer.
“The colon and rectum differ greatly. The contents of the colon may play a role and could interact and result in the development of cancer. This does not apply to rectal cancer, because the rectum normally only contacts the contents of the colon during defecation,” explains Thorkild I.A. Sørensen.
Long-term obesity increases the risk of colon cancer
To follow up the study in the European Journal of Epidemiology, the researchers conducted another study examining how changes in BMI throughout childhood and into adulthood are associated with the risk of developing colon cancer. This study has been published in the International Journal of Obesity.
The researchers used the data from school records for the birth years 1930–1972 and data from the medical examinations conducted by medical conscription boards among men in young adulthood. This method enabled them to determine the BMI of 65,000 men at three points in their young lives: 7, 13 and about 20 years.
Of these 65,000 men, 751 developed colon cancer as adults. The researchers found that the men who had been were overweight at age 7, 13 and 20 years had almost three times higher risk of developing colon cancer than the men who had not been overweight at any of the three times. Conversely, the increased risk almost completely disappeared if the men had either lost weight from the age of 13 to 20 years or if they had been overweight at 20 years old, but not as children.
“The important message is that long-term obesity seems to be the decisive factor in increasing the risk of colon cancer. The risk disappears if overweight is eliminated. Further, a person who was not overweight as a child but becomes overweight later in life may not have a similarly increased risk,” says Thorkild I.A. Sørensen.
Results should lead to interventions on childhood obesity
Thorkild I.A. Sørensen emphasizes four aspects of the new research results.
• He hopes that the results will inspire other researchers to examine this topic in greater depth and to help discover why the development of colon cancer is associated with overweight and obesity.
• The study indicates a topic that should be examined further: something may happen as children become overweight that increases the risk of developing various types of cancer in adulthood if the overweight is not eliminated in time.
• The research definitely demonstrates that being overweight has major health consequences for children. This should therefore be on the health policy agenda.
• Finally, cancer is an economic burden for society, and early interventions on childhood obesity may therefore bring economic benefits in the long term – also because many other costly conditions are associated with obesity, such as heart disease and diabetes.
“It may potentially be far better for the population and much less expensive to treat children for obesity – or, even better, prevent them from becoming overweight – than treating people for the many diseases arising later in life. Early effective interventions would clearly be better,” concludes Thorkild I.A. Sørensen.
“Childhood body mass index and height in relation to site-specific risks of colorectal cancers in adult life” was published in European Journal of Epidemiology. Thorkild I.A. Sørensen, a co-author of the article, is affiliated with the Novo Nordisk Foundation Center for Basic Metabolic Research.