Study Links Birth Weight and Older Fathers to Surge in Young Bowel Cancer Cases

Scientists have finally identified a key factor driving the surge in bowel cancer cases among people under 50. This breakthrough sheds light on a mystery that has long puzzled medical experts.

A new study from the Yale School of Public Health reveals that babies born with excess weight face a significantly higher risk of developing the disease later in life.

The incidence of bowel cancer in the UK is climbing rapidly, yet the root causes have remained unclear for years. Researchers discovered that being born overweight combined with having an older father markedly increases the chances of a young diagnosis.

This finding is critical because the number of 'giant babies' in the UK is rising. Foetal macrosomia, a condition meaning 'big body' in Greek, affects newborns weighing 8lb 13oz or more.

Current estimates suggest this condition now impacts roughly one in ten infants born in Britain. Experts warn that macrosomia often stems from parents who are overweight or have diabetes.

Consequently, the lifestyle choices of parents could inadvertently doom their children to a life-threatening cancer diagnosis. These results arrive four years after the death of Dame Deborah James, the renowned campaigner known as Bowel Babe.

She passed away at age 40 from the disease. Since her death in 2022, the Bowel Babe fund she inspired has raised over £20 million for cancer research.

Every year, approximately 44,000 people are diagnosed with bowel cancer in the UK. The condition, also called colorectal cancer, claims around 17,000 lives annually.

Known risk factors include obesity, sedentary habits, and alcohol consumption. Historically, research indicated that disease risk increased strictly with age.

For this reason, the NHS currently screens individuals between 50 and 74. Screening involves a biannual at-home test known as a faecal immunochemical test, or FIT.

However, recent data shows younger patients are increasingly developing this deadly illness. In Britain, those under 49 are now 50 per cent more likely to develop bowel cancer than peers in the early 1990s.

For the latest study published in the journal Cancer, researchers matched 1,221 patients diagnosed before age 39 with 61,000 cancer-free controls.

Results indicated that men are about a third more likely to develop the disease before age 50 than women, aligning with existing trends.

Researchers argue this gender gap may stem from higher levels of free testosterone, a male hormone linked to increased disease risk.

Significantly, the study provided convincing evidence that birth weight impacts bowel cancer risk substantially. In females, every half-kilogram difference in birth weight correlated with a 10 per cent increase in risk.

No statistical link was found between early-onset bowel cancer and the age of the father in male subjects. However, a distinct pattern emerged regarding paternal age—the age of the man at the time of conception. While experts admit the exact reason for this gender disparity remains unclear, they theorize it may be connected to maternal health factors, such as obesity or diabetes.

Previous research indicates that these conditions can interfere with the production of growth hormones essential during pregnancy, potentially compromising the long-term health of the child. Dr. Dimitrios Siassakos, a professor of obstetrics at University College London, notes that mothers with these health issues are more likely to give birth to what are termed "giant babies." Currently, approximately one in ten babies in the UK fall into this category.

This prevalence of larger-than-average infants may help explain why early-onset bowel cancer is becoming more common in younger age groups. The Yale study specifically identified that young women whose fathers were 35 or older at conception faced a significantly elevated risk of developing this disease early in life.

Older paternal age is already associated with various birth defects, such as cleft lips or holes in the diaphragm, with risks rising for each additional year of the father's age. Furthermore, certain cancers are becoming more frequent; prior studies showed that for every five years a father ages, the risk of a specific type of childhood leukemia increases by 13 percent. Separate investigations have also pointed to higher risks of brain and breast cancers.

Experts now suspect a similar connection exists for early-onset bowel cancer. The researchers propose this could be driven by an increase in *de novo* mutations—spontaneous genetic changes occurring in children born to older fathers. Although the study outlined several potential mechanisms, the investigators acknowledged that further research is necessary to validate these findings. They emphasized that there is likely no single cause behind the mysterious rise in early-onset cancers, suggesting a complex interplay of factors.