THMs linked to uterine cancer risk in California drinking water study
A JAMA Network Open study found higher uterine cancer risk among women with long-term exposure to some water disinfection byproducts.
By Tom Brennan · Health & Medicine Correspondent
3 min read
A long-running California study has linked THMs and uterine cancer risk, reporting that women with higher estimated exposure to the drinking-water chemicals had higher rates of the disease. The findings matter because the association appeared even when trihalomethane levels were within government legal limits, according to the study published in JAMA Network Open.
The researchers studied 53,100 women in the California Teachers Study, including teachers and administrators who had lived at the same address for at least 10 years, used a public water system and had no previous cancer or hysterectomy. They followed participants for nearly 20 years and identified 1,038 uterine cancer cases.
Instead of sampling each home’s tap water, the research team matched residential addresses to the public water systems serving those homes. The team then used government water-quality records from 1990 to 2020 to estimate 15-year average exposure to contaminants, including nitrate, arsenic, uranium, trihalomethanes and haloacetic acids.
Can THMs in drinking water raise uterine cancer risk?
The study found an association, not proof that the chemicals caused cancer. The researchers reported that women exposed to the highest THM levels had an 18% higher risk of uterine cancer overall after accounting for factors including age, body weight and smoking history.
Trihalomethanes, or THMs, form when chlorine used to disinfect water reacts with organic material. The study found the strongest THM association for endometrioid tumors, especially with chloroform; endometrioid tumors account for more than 95% of uterine cancer cases, according to the researchers.
The team also examined haloacetic acids, another group of disinfection byproducts. Higher exposure to HAAs was tied to nearly double the risk of nonendometrioid tumors, which are rarer and more aggressive, according to the study.
The researchers did not find a similar association for several other common drinking-water contaminants they assessed, including nitrate, arsenic and uranium.
Why are disinfection byproducts in tap water?
Public water systems disinfect drinking water to prevent infections from waterborne pathogens. Under the Safe Drinking Water Act, the U.S. Environmental Protection Agency sets and enforces standards for more than 90 drinking-water contaminants, according to the agency framework described by the researchers.
Legal limits do not mean every possible long-term health question has been settled. The researchers noted that contaminant standards reflect technical feasibility, cost and public-health benefits, while some tap-water contaminants have been studied as possible carcinogens or hormone disruptors.
Uterine cancer is the most common gynecological cancer in the United States and its incidence has been rising, according to the study. A separate Lancet study cited in the report projected global endometrial cancer cases could rise by nearly 50% by 2044, and the researchers said more than 69,000 U.S. women were expected to be diagnosed in 2025.
The study authors said the findings could help water utilities look for ways to reduce harmful disinfection byproducts while maintaining protection against infectious disease. They also said more research is needed because drinking-water exposure is potentially changeable and could become a prevention target if the associations are confirmed.
This story draws on original reporting from Medical Xpress.