Millions in the United States are unwittingly at risk from a cancer-associated toxin present in their tap water. However, recent scientific findings suggest that by minimizing this contamination, it’s possible to significantly cut the risk of related diseases—even after prolonged exposure.

Arsenic, a heavy metal, has infiltrated drinking water systems across the nation, with estimates indicating that between 100 million and 280 million Americans consume water tainted with it, particularly from wells.

Exposure to arsenic has been correlated with various cancers, cardiovascular issues, developmental problems in children, and skin conditions. As arsenic accumulates in the body over time, these health hazards become more pronounced.

Unlike certain toxins that the body can expel quickly, arsenic is retained in tissues such as skin, hair, nails, and internal organs. This chronic exposure, even at low levels, means the harmful effects compound, elevating disease risk over time.

Encouragingly, researchers have discovered that reducing arsenic levels in water by about 70 percent could decrease the risk of dying from chronic illnesses and cancer by over half, despite years of prior exposure.

In a comprehensive study spanning 20 years and involving nearly 11,000 adults in Bangladesh, it was found that participants who switched to water with reduced arsenic content experienced over a 50 percent drop in mortality from chronic diseases, heart disease, and cancer compared to those who continued consuming contaminated water.

Switching to safer wells reduced arsenic in drinking water by up to 70 percent and this reduction was so effective that people who switched eventually saw the same low mortality rates as people who had always used clean water. 

The study’s authors liken the health benefit to quitting smoking. The risk doesn’t vanish overnight, but it begins to decline steadily. 

Arsenic is a hidden danger in millions of kitchens. It has no taste or smell, yet it contaminates millions of Americans’ primary water source, private wells, raising the risks of cancers and heart disease (stock)

Arsenic is a silent threat. It occurs naturally in groundwater, has no taste or smell, and can seep undetected into the water supply of private wells. 

Chronic arsenic exposure is a known carcinogen, linked to skin, lung, and bladder cancer, with growing evidence showing its role in liver and prostate cancers as well.

It also significantly increases the risk of cardiovascular diseases, including heart disease, stroke, and conditions caused by narrowed or blocked arteries. 

In the US, naturally occurring arsenic in water is typically low (around 1 ppb), but in contaminated groundwater, it can exceed 1,000 ppb, according to the CDC. 

In the US the legal limit for arsenic in public water systems is 10 parts per billion. Public health experts stress that no level of arsenic is safe, as even long-term exposure to low concentrations can increase cancer risk.

Teams of researchers at New York University and Columbia University in New York City conducted the study with an average follow-up time of nearly 20 years. In that time, 1,401 people died from chronic diseases, including 256 from cancer and 730 from heart disease.

To ensure an accurate measurement of arsenic exposure and its concentration in the body, scientists report it as micrograms of arsenic per gram of creatinine (μg/g creatinine).

This method corrects for urine dilution by using creatinine, a natural waste product with a stable baseline, as a reference point, thereby providing a reliable result regardless of the amount of water a person has consumed. 

The United States Geological Survey found arsenic in nearly half of the wells tested across major US aquifers. About seven percent of wells exceeded the federal safety standard of 10 µg/L, indicating a widespread potential health risk.

The X-axis shows the change in a person’s urinary arsenic level over the study. For example, a value of -12 means a person’s urinary arsenic level dropped by 12 micrograms per gram of creatinine from their baseline measurement

Urine samples showed that, as mitigation measures were implemented, arsenic concentrations fell from an average of 283 μg/g to 132 μg/g creatinine.

For each major decrease in urinary arsenic, specifically, a reduction of 197 micrograms per gram of creatinine, the risk of death fell by 22 percent from chronic diseases, 23 percent from cardiovascular disease, and 20 percent from cancer.

They also concluded that participants who reduced their arsenic levels from high (at or above the median of 199 µg/g creatinine) to low (below that median) saw their risk of dying from chronic diseases fall by 54 percent compared to those who remained consistently highly exposed to the toxin.

To reach their conclusions, researchers took water samples and recorded geographic coordinates from all 5,966 wells within a 25-square-kilometer area of Araihazar, Bangladesh.

They recruited men who had lived in the area for at least five years. 

Researchers tracked participants from 2000 to 2018, collecting health data through repeated interviews, physical exams, and urine tests. 

During this period, public health efforts to label unsafe wells and install safe ones naturally reduced arsenic exposure for many, creating a real-world experiment to see how lowering exposure improved health. 

The researchers established familiar risk factors for specific cancers and heart disease, including a history of smoking and high body mass index, indicating obesity.

Like figure A, the graph shows that as arsenic is reduced (moving left of 0), the hazard ratio drops steadily and consistently below 1.0, indicating a continuously lower risk of cancer death 

For every unit of arsenic reduced, the drop in the risk of dying from heart disease is the largest. Even moderate reductions in arsenic lead to a significantly lower risk of CVD death

The study also concluded that if everyone with high arsenic exposure had reduced their levels, it would have prevented approximately 5.1 chronic disease deaths per 1,000 people annually. 

Over the study period, many households in the city reinstalled their own private wells. 

This typically offers safety from arsenic because the wells involved were drilled deeper to tap into aquifers that are naturally protected from the arsenic contamination found in shallow groundwater.

Dr Alexander van Geen, a researcher at the Columbia Climate School’s Lamont-Doherty Earth Observatory, said: ‘We show what happens when people who are chronically exposed to arsenic are no longer exposed.

‘You’re not just preventing deaths from future exposure, but also from past exposure.’

Their research was published in the Journal of the American Medical Association.