Having an elevated body mass index (BMI) in childhood is associated with an increased risk of developing obesity-related cancer in adulthood. This is the conclusion of a new study, which also indicates that the risk of breast cancer actually decreases with increasing BMI in childhood. It can take decades for a cancer to develop, and starting prevention early is therefore important, says the leading author.
Overweight in childhood influences health lifelong and can, after decades, result in one of 12 types of obesity-related cancers.
In a new study, researchers examined data on more than 300,000 children and linked specific BMI growth patterns during childhood with the risk of developing obesity-related cancer in adulthood.
The research shows that a BMI growth pattern with overweight or obesity during childhood increases the cancer risk in women more than that in men. However, a BMI growth pattern of overweight or obesity is associated with a lower risk of developing breast cancer.
“Our study contributes to the research indicating that some types of cancer take decades to develop. If you are diagnosed with a colon cancer at the age of 65 years, it may have been underway for 40 years since the first mutation. Investigating the association between the development of cancer and early risk factors such as BMI growth patterns during childhood are therefore relevant,” explains a researcher involved in the study, Britt Wang Jensen, Postdoctoral Fellow, in the Lifecourse Epidemiology Group at the Centre for Clinical Research and Prevention, Bispebjerg and Frederiksberg Hospital, Copenhagen.
The research has been published in JNCI: Journal of the National Cancer Institute.
More than 300,000 children
To examine the associations between BMI growth patterns during childhood and the risk of cancer, the researchers used registry data on more than 300,000 Danish children, who were measured and weighed up to 12 times between the ages of 6 and 15 years by school health doctors and nurses.
Data were obtained from the Copenhagen School Health Records Register and covered children born from 1930 to 1988.
The researchers established a BMI growth pattern for each child and grouped the children according to childhood BMI growth pattern of below average, average, above average, overweight or obesity.
The researchers linked the data from the Copenhagen School Health Records Register with data from the Danish Cancer Registry and identified children who later developed breast cancer or an obesity-related cancer, including cancers of the colon, liver, oesophagus and rectum.
The researchers followed the participants in the registers until 2018 and examined the risk of developing any of 12 types of obesity-related cancers as a combined group. Breast cancer was examined separately.
“The cancer types studied are all associated with adult obesity. However, we investigated breast cancer separately because previous studies found that childhood overweight and obesity are inversely associated with breast cancer,” says Britt Wang Jensen.
Overweight in childhood is associated with increased risk of cancer among women
During follow-up, 7,285 women developed obesity-related cancer – excluding breast cancer.
7,261 men developed obesity-related cancer.
The researchers examined the associations with BMI trajectories during childhood.
- Women with an above average childhood BMI trajectory had an 8% higher risk of obesity-related cancer versus women with an average childhood BMI trajectory.
- Women with an overweight childhood BMI trajectory had a 27% higher risk of obesity-related cancer.
- Women with an obesity childhood BMI trajectory had a 79% higher risk of obesity-related cancer.
- Men with an overweight childhood BMI trajectory had a 13% higher risk of obesity.
- Men with an obesity childhood BMI trajectory had a 30% higher risk of obesity-related cancer.
“These associations are strong. The reason why the associations are stronger for women than for men is probably because some of the cancer types that have strong associations with childhood overweight only affect women, including ovarian and uterine cancer,” explains Britt Wang Jensen.
Inflammation may link overweight and cancer
Britt Wang Jensen explains that the link between childhood overweight and obesity-related cancers is not yet understood.
One suggested link is that overweight results in a chronic state of low-grade inflammation in the body, which can result in mutations that can lead to development of cancer.
Another possibility is that overweight disrupts the balance of specific hormones, which may increase the risk of developing some types of cancer.
The researchers also examined whether the development of type 2 diabetes could affect the association between childhood overweight and the risk of obesity-related cancer later in life.
However, the researchers found no link between the two.
“We were quite surprised, but this indicates that, in relation to the later risk of cancer, the impact of type 2 diabetes for an individual with a childhood overweight trajectory is not greater than for an individual with an average childhood BMI trajectory,” says Britt Wang Jensen.
Overweight in girls inversely associated with breast cancer
The researchers also examined how the childhood BMI trajectories influenced the risk of breast cancer among women either before or after menopause.
3,812 women in the study developed breast cancer before menopause, and 6,406 did so afterwards.
The researchers found an inverse association between the BMI trajectory and the risk of breast cancer both before and after menopause.
- An overweight BMI trajectory was associated with a 20% lower risk of breast cancer before menopause versus an average BMI trajectory.
- An obesity BMI trajectory was associated with a 41% lower risk of breast cancer before menopause.
- An overweight BMI trajectory was associated with a 24% lower risk of breast cancer after menopause.
- An obesity BMI trajectory was associated with a 59% lower risk of breast cancer after menopause.
- A below-average BMI trajectory was associated with a higher risk of breast cancer both before and after menopause.
“This association has been found before, and we wonder why there is this inverse association between BMI and breast cancer. Some studies have suggested that the amount of body fat during childhood affects the development of the breast tissue and that this may influence a woman’s risk of developing breast cancer later in life. These results do not mean that we recommend young girls to gain weight as a way of preventing breast cancer,” explains Britt Wang Jensen.
According to Britt Wang Jensen, the study provides insight into how childhood BMI trajectories are not only relevant in childhood but may have lifelong effects.
“Avoiding some of these types of cancer requires starting prevention early, so that fewer children develop overweight and obesity, with the accompanying risk of cancer later in life,” concludes Britt Wang Jensen.
