Exposure to obesity in the womb puts babies at higher risk of developing bowel cancer as adults

LONDON — Babies of overweight women are more than twice as likely to develop bowel cancer when they reach adulthood, a new study warns. Researchers examining more than 18,000 mother and child pairs suggests that conditions babies experience while in the womb can be key risk factors for the disease later on. Study authors say that their findings may help to explain rising rates of bowel cancer among younger adults.

In many high-income countries, new cases and deaths from bowel cancer have fallen or plateaued in older adults. However, have nearly doubled in younger adults, while those rates have risen rapidly across all age groups in low and middle-income countries. As a result, estimates show the global burden of bowel cancer may increase by 60 percent, to more than 2.2 million new diagnoses and 1.1 million deaths by 2030.

Scientists believe fetal programming is a factor in several health conditions across the course of life, including cardiovascular disease and diabetes. Previous research suggests that fetal exposure to obesity in the womb may also have a role in cancer risk.

The researchers looked at more than 18,000 mother and child pairs in the United States to see if maternal obesity, pregnancy weight gain, and high birth weight may play a role in bowel cancer risk. The mothers provided background information on prenatal visits, diagnosed conditions, and prescribed medications from six months before pregnancy to delivery.

Study authors classified the mothers’ weight (or Body Mass Index) “underweight” (BMI under 18.5), “healthy” (BMI of 18.5–24.9), overweight (BMI of 25– 29.9), or obese (BMI of 30 or above). They recorded weight gain — the rate of early weight gain, or pounds gained each week up to and including 32 weeks of pregnancy — and total weight gain, or the difference between the last weight before giving birth and that recorded at the first prenatal visit. The team also categorized birthweight as low if it was 4.4 pounds or below; average if between 4.4 and 8.8 pounds; and high for anything above that.

More cases of early onset bowel cancer diagnoses

The offspring were then monitored for 60 years from birth until 2019 through linkage with the California Cancer Registry. Nearly half of the children (48%) were born in the early 1960s. About a third (34%) were ethnic minorities and just over half (52%) came from families with an annual income below the national average.

During the monitoring period, doctors diagnosed 68 children with bowel cancer between 1986 and 2017, when they were between 18 and 56 years-old. About half (48.5%) were diagnosed before the age of 50. Nearly one in five had a family history of bowel cancer. A higher proportion of obese mothers (16%) had offspring weighing 8.8 pounds or more at birth than did underweight, healthy weight (7.5%), or overweight mothers (11%).

“Compared with being underweight or a healthy weight, overweight and obesity were associated with a more than doubling in the risk of bowel cancer in the offspring. Bowel cancer rates were 16.2/100,000, 14.8/100,000, and 6.7/100,000 in the adult offspring of obese, overweight, and underweight/healthy weight mothers, respectively,” study authors write in a media release.

“While early weight gain wasn’t associated with bowel cancer risk, total weight gain was, with a doubling in risk for a gain of 23 to 29 pounds. However, a high rate of early weight gain was associated with a quadrupling in risk among the offspring of mothers whose total weight gain had been low, but not among those whose total weight gain had been high. The risk was also heightened among those whose birth weight was 4,000g [8.8 pounds] or more compared with those within a healthy weight range at birth,” the team continues.

What’s causing this link to cancer?

Associate Professor Caitlin Murphy from the Houston School of Public Health adds this was an observational study and as such can’t establish a cause for this link. However, the team notes the findings suggest that “the well-established relationship between obesity and colorectal cancer may have origins in periods that begin before birth.”

Murphy explains that nutrients received in the womb may permanently alter the structure and function of fat tissue, appetite regulation, and metabolism, while excess exposure to insulin and growth hormones may affect insulin sensitivity.

“Our results provide compelling evidence that in utero events are important risk factors of [colorectal cancer] and may contribute to increasing incidence rates in younger adults,” the researchers say. “There may also be other as yet unknown exposures during gestation and early life that give rise to this disease and warrant further study.”

“Given population trends in maternal obesity, which has multiplied in prevalence by nearly six since the 1960s, we may see a growing burden of early-onset [bowel cancer] for decades to come.”

The study appears in the journal Gut.

South West News Service writer Stephen Beech contributed to this report.