Colorectal cancer: Overweight young people at risk

Poor diet, sedentary behaviour and obesity in adulthood have been linked to a higher risk of developing multiple cancers, including colon and rectal cancer. Now, scientists in China have shown that the risks of developing colon cancer may be related to being overweight before the age of 30.  

Colorectal cancer rates vary considerably from country to country, with the highest number of cases in Australia and New Zealand, and incidence rates rising in Asia, South America and Eastern Europe. Excess body fat in adulthood has long been associated with colorectal cancer risk, possibly due to the associated hormonal imbalances and inflammation, which have an impact on metabolic health. However, little is known about whether having a high body mass index (BMI) under the age of 30 influences the chances of developing colorectal cancer later. 

“It would be incredibly helpful to know how body fatness affects the development of colorectal cancer throughout the human lifespan to improve prevention strategies for this cancer,” says Khemayanto Hidayat at the First Affiliated Hospital of Soochow University in Suzhou, China, who worked on the study with co-workers Chun-Mei Yang and Bi-Min Shi.  

The team conducted a meta-analysis of data collected during 15 studies from 1992 to 2016, covering 17,754 people under the age of 30 from predominantly Western countries. They found a 17 percent higher risk of developing colorectal cancer in men and 8 percent higher risk in women for every 5kg/m² increase in BMI.  

“The exact reasons for these sex-specific discrepancies remain unclear,” says Shi. “However, it may be that difference in body composition between men and women, and possibly the protective influence of oestrogen in hormone replacement therapy in postmenopausal women, could explain gender differences.” 

The team also found that excess body fat at an early age is more strongly associated with colon cancer risk than with rectal cancer risk.  

Colorectal cancers can take many years to develop and spread, so it is possible that pre-cancerous lesions may start at a young age. Shi’s team calls for further international research into links of body fatness with cancer to pinpoint the times in life where excess body fat is most detrimental.  

“Our findings indicate that we should perhaps be intervening sooner than mid- and late- adulthood,” says Shi. “Educating young people about the dangers related to weight gain and obesity should be a global health priority.” 

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