Understanding how childhood factors may affect bowel cancer risk in adulthood

A new paper by the World Cancer Research Fund International (WCRFI) has identified that an increased birth weight, or higher body mass index (BMI) during childhood, adolescence or young adulthood is associated with an increased risk of developing bowel cancer in later life.

Commissioned as part of the WCRFI’s Global Cancer Update Programme (CUP Global), the paper is a comprehensive systematic review and meta-analysis of 37 publications. It is the first review to examine how factors in childhood, such as weight, height and BMI, may link to increased risk of bowel cancer later in life.

This is an important new area for analysis, as the majority of research to date focuses on how behaviours in adult populations may impact bowel cancer onset. While bowel cancer is traditionally viewed as an older population disease, Australia has the highest rates of early-onset bowel cancer in the world, meaning that research is urgently needed to investigate for clues to disease development earlier in life.

This paper is part of a growing field of research investigating how childhood health factors and behaviours may influence bowel health in later life to assess whether interventions in childhood diet, nutrition, physical activity and body weight may lay the groundwork for positive or poor bowel health later on. For example, other recent research has identified that childhood exposure to an E. coli toxin is linked to greater risk of bowel cancer development later in life.

The WCRFI study analysed four early life age groups, with findings including:

• Birth size: Normal considered to be between 2500g-4000gm. Each 1kg increase in birthweight was associated with a 9% increased risk in bowel and rectal cancer risk.

• Childhood 2-9yrs: Each 1 standard deviation increase in BMI was associated with an increased risk of developing bowel cancer.

• Adolescence 10-19yrs: Each 1 standard deviation increase or each 5kg/m² increase in BMI was associated with a 5-18% increased bowel and rectal cancer risk.

• Early adulthood 18-25yrs: Each 5kg/m² increase in BMI was associated with a 12% increased risk of bowel and rectal cancer.

While the pathophysiological implications of higher weight, BMI, and adiposity during early life on bowel cancer development are not fully understood, these may be responsible for increased inflammation and higher circulating levels of pro-inflammatory markers resulting in chronic low-grade inflammation that may encourage tumour growth. This aligns with findings for adult obesity links to bowel cancer risk.

There are some limitations to this analysis. For example, it’s unclear whether the association between early life adiposity and bowel cancer risk can be seen as an independent finding, because individuals who are obese in childhood are often also obese in adulthood due to behavioural, environmental and genetic factors.

We know that obesity in adulthood is a risk factor for bowel cancer, and therefore cannot assume this new finding regarding childhood weight and adiposity is conclusive of bowel cancer risk.

While further research is required, the paper does conclude that there is strong probable evidence for links between higher birth weight and early life BMI with an increased risk of bowel cancer.

Cancer is a complex condition that develops over decades. The better we can understand its early origins, the better we can provide effective education and prevention measures to address potential contributing factors.

Studies, such as this one, are starting to fill gaps in research to help us better understand and therefore address early indications and cancer risk behaviours.

This study highlights the potential impact of BMI and health behaviours throughout life and the importance of maintaining good diet and behaviour habits for long-term health and to reduce bowel cancer risk.