Discover the surprising link between BMI and colorectal cancer risk in Asia—and what it could mean for your health and cancer prevention strategies.
Study: Body Mass Index and Risk of Colorectal Cancer Incidence and Mortality in Asia. Image Credit: Kateryna Kon / Shutterstock.com
In a recent study published in JAMA Network Open, researchers report that body mass index (BMI) values in Asians population may predict the risk of developing colorectal cancer (CRC).
Colorectal cancer
CRC comprises up to 10% of all cancers worldwide and 9.4% of cancer-related deaths. With 1.9 million new CRC cases reported in 2020 alone, researchers estimate that 3.2 million CRC cases will be reported by 2040.
CRC is more likely to be diagnosed in wealthier countries, as it is mediated by changes in the lifestyle, environmental chemicals, and dietary patterns of their inhabitants. As Asian countries shift towards a more Westernized lifestyle and diet, their risk of CRC has also risen.
Like CRC, obesity risk is has also risen throughout the world. This phenomenon has similarly been attributed due to the adoption of a Westernized lifestyle that is driven by consumerism and the increased availability of fast food.
About the study
Previously, researchers reported an increased risk of CRC among both among overweight or obese people in Asia, as well as underweight individuals, as compared to normal-weight people with BMI values between 18 and 23 kg/m2. Risk factors for CRC include obesity, being male, a family history of cancer, and smoking.
With little data from Asian populations, the present study sought to identify strong evidence of an association between BMI, the risk of CRC occurrence, and CRC-related death. To this end, 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 for CRC risk and CRC-related mortality, respectively, who participated in 17 prospective studies that were part of the Consortium. The average 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, along with 4,550 CRC-related deaths. CRC risk was found to rise with BMI in a dose-dependent manner.
As compared to individuals with a BMI value between 23 and 25 kg/m2, the CRC risk was 9% higher among those with a BMI between 25-27.5 kg/m2. CRC risk was further increased by 19% and 32% among individuals with BMI values between 27.5-30 kg/m2 and over 30 kg/m2, respectively. These increases were not affected by adjustments made for demographic, lifestyle, and medical factors, including smoking, drinking, and diabetes mellitus.
The risk of CRC-related mortality increased as BMI rose above 27.5 kg/m2. CRC-related mortality was also higher by 18% and 38% with BMI values between 27.5-30 kg/m2 and over 30 kg/m2, respectively.
The risk of new-onset CRC with increasing BMI rose was more striking for colon cancer as compared to rectal cancer. High BMI was associated with increased CRC rates among men as compared to women.
CRC-related deaths were higher only among men with BMI values exceeding 30 kg/m2. This subgroup showed a J-shaped curve, even after adjusting for education, medical, and lifestyle factors, which may be due to an increased risk of central obesity among men as compared to women.
CRC-related mortality was higher among men if they were current smokers or drinkers as compared to women. Only 6% of women, as compared to 51% of men, were current smokers. This sex-differential outcome might be due to higher screening rates among women or reduced hormone replacement therapy (HRT) use among Asian women, as HRT use is a risk factor for CRC.
Conclusions
BMI is associated with increasing CRC incidence and CRC-related mortality risk among Asians. The link between higher BMI and increased CRC-related mortality is also corroborative of prior studies conducted in China, Iran, and Japan. These findings may clarify how the growing prevalence of obesity is reflected in increased illness and death rates from CRC in this population.
Obesity leads to lipid peroxidation and disrupted metabolism, both of which may increase the expression cancer-causing genes. The pathways most often implicated in this process relate to glucose and insulin secretion, which may mediate the increased CRC risk.
Obesity is also characterized by low-grade inflammation, which can stimulate the release of cytokines initiate cancerous cell pathways involved in CRC initiation, progression, and distant spread. Excess nutrients in obesity also supports malignant transformation by activating cell growth.
Importantly, the current study identifies an increased risk of CRC among individuals, irrespective of their diabetes status. Thus, CRC risk is not mediated by glucose metabolism to the same extent as it is by increased BMI.
Individuals in East Asia have a leaner body habitus and higher incidence rates of diabetes, even without crossing the Western threshold for obesity. These individuals are also more likely to have central obesity, which is a strong risk factor for type 2 diabetes that also increases the risk of CRC.
Thus, BMI cutoff values must be utilized when assessing the risk of CRC in this patient population in future research. More detailed studies that monitor tumor stage and treatment regimens, as well as longitudinal follow-up, will help to validate and confirm these findings.
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