Chemicals in drinking water may increase risk of uterine cancer
In a recent study, researchers examined whether certain chemicals present in public drinking water are linked to uterine cancer, the most common gynecological cancer in the United States and one that has been steadily increasing in incidence.
After following 53,100 California teachers and administrators for nearly 20 years, researchers found that long-term exposure to certain drinking water disinfectant byproducts was linked to a higher risk of uterine cancer. The risk was greatest among women living in areas with higher levels of trihalomethanes (THMs), chemicals formed when chlorine reacts with organic matter in water. This increased risk remained even when THM levels were within the government's legal limits.
The findings are published in JAMA Network Open.
The unequal cancer burden
Drinking water is one of the most highly regulated resources in the United States. Under the Safe Drinking Water Act, the Environmental Protection Agency (EPA) sets and enforces standards for more than 90 contaminants to help ensure that drinking water is safe and protects public health. However, studies have suggested that tap water can expose people to chemicals that are hormone disruptors and potentially carcinogenic.
Endometrial or uterine cancer is the sixth most common cancer among women worldwide, yet it remains largely absent from global health strategies. According to a Lancet study, the number of cases is expected to rise by nearly 50% by 2044. In the United States alone, more than 69,000 women will be diagnosed in 2025, accounting for 3.4% of all new cancer cases.
The burden of endometrial cancer is not experienced equally. Black women are more likely to be diagnosed with advanced-stage disease and have higher mortality rates than white women. Geography also plays a role, as the rates and types of uterine cancer vary substantially across the United States.
The most common type, endometrioid tumor, is seen most often in the Midwest and Appalachia, while rarer and more aggressive nonendometrioid tumors are more common in the South and Northeast.
These striking variations from region to region suggest that environmental exposures could play a role. Drinking water is a likely contributor, since it can carry contaminants that are known or suspected to cause cancer. While there are legal limits for contaminants, these limits are set based on what's technically possible, affordable and beneficial for health.
Common contaminants include natural substances like nitrate, arsenic and uranium, as well as byproducts created during water disinfection, such as THMs and haloacetic acids (HAA).
Hidden threats in tap water
Very few studies have tested whether drinking-water contaminants are linked to uterine cancer, so the researchers decided to do so. They used a long-term approach to see if there was a link between drinking water and cancer. They analyzed data only from a large group of women called the California Teachers Study, who had lived at the same address for at least 10 years, received water from a public water system and had no prior history of cancer or hysterectomy.
Rather than testing water from each participant's tap, the researchers linked home addresses to the Community Water System serving each residence and used government water quality records from 1990 to 2020. They then calculated each participant's estimated 15-year average exposure to contaminants, including nitrate, arsenic, uranium and chlorine disinfection byproducts, THMs and HAAs.
They linked participants' names in the California Cancer Registry with estimated contaminant exposure, while accounting for age, body weight and smoking history.
Among the study population, 1,038 women developed uterine cancer. The analysis found that exposure to certain chemicals used to disinfect public drinking water was associated with a higher risk of uterine cancer. In contrast, no association was found with other common contaminants, including nitrate, arsenic or uranium.
THMs, particularly chloroform, showed the strongest association with endometrioid tumors, which account for more than 95% of uterine cancer cases. Women exposed to the highest levels of THMs had an 18% higher risk of uterine cancer overall. Higher exposure to HAAs was associated with nearly twice the risk of developing nonendometrioid tumors.
The findings could help water utilities explore ways to reduce harmful disinfection byproducts while continuing to protect communities from waterborne infections. The results show an association between these chemicals in drinking water and uterine cancer risk, but they do not establish that they cause cancer.
Future studies are needed to better understand these relationships, especially since exposure to drinking water contaminants is potentially modifiable and may provide an important area for prevention.
This article was originally published on MedicalXpress Breaking News-and-Events.