Environmental Toxicants and Colorectal Cancer

Colorectal cancer (CRC) is the second leading cause of cancer-related deaths worldwide,¹ and incidence of early-onset CRC continues to increase in the US and other industrialized countries.² Younger patients diagnosed with CRC often present with advanced disease, which has led to an increase in CRC-related deaths in patients under 50 years of age.³ Recent US reporting also indicates that CRC incidence, survival, and mortality vary substantially by race and ethnicity.⁴ In addition to genetic predisposition, several lifestyle-based factors have been associated with an increased risk of developing CRC, from increased alcohol intake and sedentary behaviors to decreased fiber and plant consumption and physical activity levels.^5,6

Research studies also suggest connections between some environmental pollutants and CRC risk. How can a functional medicine approach and lifestyle modification help to reduce chronic toxicant exposures, enhance the body’s biotransformation and detoxification pathways, and help to reduce the risk of CRC development?

Pollutants and CRC: From Pesticides to Particulates

Studies continue to investigate whether environmental toxicant exposures elevate the risk of CRC. Recent research investigating links between pesticide exposures and CRC have not shown definitive associations; however, results suggest that some of these chemicals may play a role.⁷ A 2021 systematic review examined pesticide exposures and CRC risk, evaluating 139 studies that included participant populations such as farmers, pesticide manufacturers, people in rural communities, and those who consumed foods with pesticide residues.⁸ While overall results showed a similar number of significant positive and inverse associations, researchers identified specific pesticides that are legally used in the US that were also associated with an elevated colon, rectal, or colorectal cancer risk such as terbufos, dicamba, trifluralin, S-ethyl dipropylthiocarbamate (EPTC), imazethapyr, chlorpyrifos, carbaryl, pendimethalin, and acetochlor.⁸

Hazardous chemical exposures, including asbestos,⁹ industrial complex pollutants,¹⁰ and air pollution particulates¹¹ may also increase the risk of CRC development. A 2022 meta-analysis investigating links between outdoor particulate matter (PM) air pollution and increased risks of gastrointestinal cancers found that exposure to PM_2.5 was associated with a 12% increased risk of gastrointestinal cancer overall and a 35% increased risk of colorectal cancer.¹¹ Due to limitations in the analysis, researchers were not able to determine if the elevated cancer risks were due to acute or chronic exposures.

EDCs in Personal Care Products & CRC Risk

Chemical ingredients present in some personal care products have been identified as endocrine-disrupting chemicals (EDCs) and have been associated with an increased risk of various cancers.^12,13 Specific to colon and rectal cancers, a human cell study determined that the EDC bisphenol A (BPA) promoted the proliferation, migration, and tumor growth of colon cancer cells in both in vitro and in vivo evaluations.¹⁴ Other EDCs commonly used in personal care products, such as phthalates, have been associated with CRC risk. A 2021 study (n=221) compared the concentrations of urinary phthalate metabolites between healthy participants, patients with colorectal adenomas, and patients with CRC.¹⁵ Study results indicated a significantly higher urinary phthalate metabolite concentration in patients with CRC compared to patients with adenoma or healthy individuals.¹⁵ Researchers concluded that higher exposure levels to phthalates may contribute to CRC incidence.¹⁵

Recently, a mouse model was used to study another chemical frequently seen in common personal care products, triclocarban.¹⁶ Low-dose exposure to this chemical, which has similar properties to the EDC triclosan,¹⁷ was found to increase the severity of colitis and promote the development of colitis-associated colon cancer through gut microbiota mechanisms.¹⁶

Health Inequities in Cancer Risk, Diagnosis, and Access to Treatments

Studies continue to report that hazardous chemical exposures from sources such as industrial pollutants and personal care products disproportionately impact communities of color.^18-21 For example, a 2020 observational study (n=46,709 women; ages 35-74) found that compared to non-use, permanent hair dye use was associated with a 45% higher breast cancer risk in Black women (CI: 1.10-1.90) and a 7% higher risk in white women (CI: 0.99-1.16).²² In addition to breast cancer, research continues to highlight racial health inequities in risk, diagnosis, and care for a variety of cancers, from lung and thyroid cancers to leukemia.^23-26 In fact, the American Society of Clinical Oncology (ASCO) recently reported on treatment inequities for cancers such as leukemia and lymphoma that often use bone marrow transplants.²⁷ According to the ASCO, due to a lack of ethnic and racial diversity in the volunteer bone marrow donor registry, a white patient has a 77% chance of finding a bone marrow match while a Black person only has a 23% chance of finding a matched donor. Asian and Pacific Islander patients have a 41% chance, Hispanic or Latino patients have a 46% chance, and American Indian and Alaska Native (AIAN) patients have a 57% chance of finding a matched donor.²⁷

Regarding colorectal cancer, incidence, survival, and mortality rates vary substantially in the US by race and ethnicity, with the highest incidence and mortality among AIAN and non-Hispanic Black individuals.⁴ As an example, CRC mortality rates are 46% higher in AIAN men and 44% higher in Black men compared to white men. In addition, Black individuals are more likely to be diagnosed with metastatic CRC (25%) compared to white individuals (21%), and Black individuals are less likely to receive either timely follow-up after a positive stool test or a high-quality colonoscopy.⁴ Recent reporting has also emphasized the growing inequity in early-onset CRC reflected by steep diagnosis increases among indigenous Alaskans, growing from 18.8 cases per 100,000 individuals aged 20 to 49 years during 1998 through 2002 to 34.8 cases per 100,000 during 2014 through 2018.²⁸

Lifestyle-Based Approaches to Health and Reducing CRC Risk

Due to the potential increased CRC risk associated with some environmental toxicants, reducing levels of exposure while supporting the body’s detoxification and elimination pathways are possible health strategies. In the functional medicine model, assessment of a patient’s total toxic load and recognizing ongoing exposures are essential pieces of personalized therapeutic treatments. The Toxin Exposure Questionnaire is a tool within the extensive IFM Toolkit, available to IFM members, that tracks a patient’s vulnerability to harmful chemicals and the progress of therapeutic interventions. In addition, optimizing a patient’s nutritional status, ensuring adequate fiber and water intake, eating more phytonutrient-dense and diverse foods, and supporting liver function through targeted, nutrient-dense diets such as IFM’s Detox Therapeutic Food Plan are all dietary treatment approaches within the functional medicine model that may help to improve the elimination of toxic compounds and to alleviate toxic burden.

Preventative CRC screenings as well as nutrient-dense diets high in fruit, vegetables, and whole grains and low in animal fats have been recommended for reducing risk of colon and rectum cancers.²⁹ A recent meta-analysis of 49 observational studies (n=3,059,009 total participants) found that a plant-based diet significantly reduced the risk of colorectal, rectal, and colon cancers by 24%, 16%, and 12%, respectively.³⁰ In addition, a 2022 meta-analysis found that increasing soluble and insoluble fiber consumption was protective against CRC.³¹ Other studies have evaluated the impact of specific nutrients on CRC risk. A 2022 case-control study (n=207 CRC cases and 220 controls) suggested that consumption of dietary antioxidants such as vitamins A, C, E, zinc, selenium, and manganese from a high-quality diet may significantly reduce odds of CRC incidence.³² Further, a 2023 meta-analysis of 28 observational studies found an inverse association between circulating vitamin D levels and CRC risk, ranging from a 20 to 39% reduced risk.³³

At IFM’s Environmental Health Advanced Practice Module (APM), learn more about how your patient’s physical environment and toxicant exposure levels may impact their health outcomes and what lifestyle-based tools may benefit their wellness path.