Discover the surprising link between body mass index (BMI) and colon cancer risk in Asia—and what it could mean for your health and cancer prevention strategies.

Test: Body mass index and risk of colorectal cancer incidence and mortality in Asia. Photo source: Kateryna Kon / Shutterstock.com

In a recent study published in JAMA network openScientists report that body mass index (BMI) values ​​in the Asian population may predict the risk of developing colorectal cancer (CRC).

Colon cancer

CRC accounts for up to 10% of all cancers worldwide and 9.4% of cancer-related deaths. With 1.9 million new cases of CRC reported in 2020 alone, researchers estimate that 3.2 million cases of CRC will be reported by 2040.

The likelihood of being diagnosed with CRC is higher in wealthier countries, as it is mediated by changes in lifestyle, environmental chemicals, and dietary patterns of their inhabitants. As Asian countries have changed to a more Westernized lifestyle and diet, the risk of developing CRC has also increased.

Like CRC, the risk of obesity has also increased worldwide. This phenomenon is also attributed to the adoption of a Western lifestyle, which is fueled by consumerism and the increased availability of fast food.

About the study

Previously, researchers reported an increased risk of colon cancer in overweight or obese people in Asia, as well as in underweight people, compared with those of normal weight, with a BMI of 18 to 23 kg/m2.²Risk factors for colon cancer include obesity, male gender, family history of cancer, and smoking.

Given the paucity of data from Asian populations, this study aimed to identify strong evidence for an association between BMI, CRC risk, and CRC-related mortality. For this purpose, data were obtained from the Asia Cohort Consortium to identify any associations that may exist between BMI, CRC risk, and CRC-related mortality.

The current study included 619,981 participants and 650,195 participants on the risk of CRC and CRC-related mortality who participated in 17 prospective studies that were part of the Consortium. The mean follow-up period was 15 years.

What were the findings?

A total of 11,900 new cases of CRC were reported during the study period, as well as 4,550 deaths related to CRC. The risk of CRC was found to increase with BMI in a dose-dependent manner.

Compared to people with a BMI between 23 and 25 kg/m²The risk of colon cancer was 9% higher in people with a body mass index (BMI) of 25–27.5 kg/m²The risk of colon cancer increased by 19% and 32% in people with BMI values ​​between 27.5-30 kg/m² and over 30 kg/m²respectively. These increases were not affected by adjustments for demographic, lifestyle and medical factors, including smoking, alcohol drinking and diabetes.

The risk of death from colorectal cancer increased with BMI above 27.5 kg/m²Colorectal cancer-related mortality was also increased by 18% and 38% at BMI values ​​between 27.5-30 kg/m² and over 30 kg/m²appropriately.

The risk of new CRC with increasing BMI increased more strikingly for colon cancer compared with rectal cancer. High BMI was associated with increased rates of CRC in men compared with women.

The number of deaths related to colorectal cancer was higher only among men with a BMI above 30 kg/m². This subgroup showed a J-shaped curve, even after adjusting for education, health care, and lifestyle factors, which may be due to the increased risk of central obesity in men compared with women.

CRC-related mortality was higher among men who were current smokers or alcohol drinkers compared with women. Only 6% of women, compared with 51% of men, were current smokers. This gender difference in results may be due to higher screening rates among women or reduced use of hormone replacement therapy (HRT) among Asian women, as HRT use is a risk factor for CRC.

Conclusions

BMI is associated with increased CRC incidence and mortality risk among Asians. The association between higher BMI and increased CRC mortality also confirms previous studies conducted in China, Iran, and Japan. These results may explain how the increasing prevalence of obesity translates into increased CRC incidence and mortality in this population.

Obesity leads to lipid peroxidation and impaired metabolism, which may increase the expression of cancer-causing genes. The pathways most commonly implicated in this process involve glucose and insulin secretion, which may mediate increased CRC risk.

Obesity is also characterized by low-grade inflammation, which can stimulate the release of cytokines that initiate cancer cell pathways involved in CRC initiation, progression, and distant dissemination. Excessive nutrients in obesity also support malignant transformation by activating cell growth.

Importantly, the current study identifies an increased risk of CRC in individuals regardless of their diabetes status. Thus, CRC risk is not mediated by glucose metabolism to the same extent as by increased BMI.

East Asians have leaner bodies and higher rates of diabetes, even without meeting the Western obesity threshold. They are also more likely to have central obesity, which is a strong risk factor for type 2 diabetes and also increases the risk of CRC.

Therefore, BMI cutoff values ​​need to be used to assess CRC risk in this patient population in future studies. More detailed studies monitoring tumor stage and treatment regimens, as well as long-term follow-up, will help verify and confirm these findings.