Obese mothers-to-be may double their offspring’s risk of developing colorectal cancer (CRC) as adults, a study of 18,000 mother and child pairs has shown.

The findings suggested the well-established relationship between obesity and CRC may have origins before birth and could be contributing to the increasing incidence of CRC in younger adults, the US researchers warned.

‘This process may occur through fetal programming, the concept that the maternal environment determines the risk of disease in later stages via developmental, genetic and epigenetic changes,’ they wrote last week (23August]) in Gut.

Researchers used data from women who gave birth in Oakland, California between 1959 and 1966 and then used the California Cancer Register to analyse CRC diagnoses in adult offspring over several decades of follow-up.

Between 1986 and 2017, they found 68 adult offspring were diagnosed with CRC with about half (48%) of cases diagnosed in people aged under 50 years.

Bowel cancer rates were 16.2/100,000 in obese women’s adult offspring and 14.8/100,000 for overweight women’s children compared with 6.7/100,000 among the offspring of healthy and underweight women.

The rate that women gained weight during pregnancy also had a bearing on CRC risk, the researchers found.

‘Like maternal obesity, pregnancy weight gain may increase the risk of obesity in offspring, but the modification of rate of early weight gain by total weight gain suggests the timing of weight gain may be most important,’ they wrote.

CRC risk was also increased among the adult offspring who weighed 4000g or more at birth, compared with offspring who were an average weight at birth (2000-3999g), they noted.

‘Our findings suggest maternal obesity and pregnancy weight gain may contribute to increasing incidence rates of CRC in younger (age á 50 years) adults. Incidence rates of early-onset CRC have increased across successive generations, implicating exposure increasingly prevalent in early life – critical periods of growth and development, such as gestation, infancy and childhood,’ they concluded.

‘Given population trends in maternal obesity, which has multiplied in prevalence by six since the 1960s, we may see a growing burden of early-onset CRC for decades to come.’

Other factors in early life, such as environmental toxins, medications, chronic conditions, and microbiome, and that are likely related to maternal obesity, may also contribute to early-onset cancers, they added.

‘There may also other as yet unknown exposures during gestation and early life that give rise to this disease and warrant further study,’ they said.

Earlier this year, the British Heart Foundation said there were around 32,000 heart and circulatory deaths as a result of excess weight and obesity every year.