In the mid-1970s, environmental health advocates began to pressure the Food and Drug Administration (FDA) to ban red dye 2.
They argued that the food dye had been linked to cancer. FDA officials, however, said there was no conclusive evidence that the dye caused cancer.
The agency eventually banned the dye, not because it caused cancer, but because questions remained.
This story arc has become quite common when it comes to environmental health, most recently with the plastics ingredient bisphenol-A (BPA).
It’s challenging to get clear answers to this kind of question. Scientists can’t expose large groups of people to suspected carcinogens, pairing them with a control group, to see what happens.
But a new meta-analysis used an innovative approach to look at studies done on the safety of chemicals, including acetaminophen, plastics, pesticides, and nanotechnology.
The findings suggest that many common chemicals cause cancer, even at levels that people are commonly exposed to them.
The study, published today in the Journal of Carcinogenesis, explored the genetic and cellular effects of 85 common chemicals. It considered whether chemicals that might appear safe when studied in isolation could combine to lay the groundwork for cancer.
A Closer Look at Cancer Risks
The research begins to fill in gaps in our understanding of what causes cancer.
“While there has been a considerable body of research on occupational and high-dose exposure to environmental chemicals and cancer risk that has resulted in important regulations to limit these exposures, less is known about low-dose exposures and mixtures of low-dose exposures to the general public,” said Susan Gapstur, Ph.D., MPH, vice president of the epidemiology research program at the American Cancer Society.
The project brought together hundreds of experts, each a specialist in a particular cellular process that makes cancer different from normal cell behavior. The experts identified a handful of chemicals that could contribute to each process. They then looked at previous research on those chemicals.
They found that nearly 60 percent of the chemicals they studied could have damaging effects at exposure levels commonly seen in the real world.
These included the weed killer atrazine and the pain medication acetaminophen.
Fifteen percent of the chemicals — including BPA, carbon nanotubes, the blood pressure medication reserpine, and various pesticides and heavy metals — also had a predictable dose-response pattern, which scientists see as strong evidence of causality.
Few of the chemicals the study identified had ever been identified as causing cancer.
That may be because current methods for testing chemicals were developed before scientists gained a more nuanced understanding of how cancer works.
“Our current understanding of the biology of cancer suggests that the cumulative effects of (non carcinogenic) chemicals acting on different pathways that are relevant to cancer, and on a variety of cancer-relevant systems, organs, tissues, and cells could conspire to produce carcinogenic synergies that will be overlooked using current risk assessment methods,” the researchers wrote.
An In-Depth Look at Cell Signaling
The analysis looked at the unique cell signaling that allows cancer cells to grow and to evade the body’s immunological checks and balances.
It also considered whether the chemicals can cause genetic mutations that lead to cancer, whether they can create a favorable cellular “microenvironment” for cancer, and whether they can facilitate the production of new blood vessels that a tumor needs to survive.
With these new considerations, it appears that the standards government and international health groups use to determine whether chemicals are safe are not adequate.
Those methods only consider chemicals in isolation. They would overlook, for example, a chemical that spurs genetic mutations that make cancer more likely when a second chemical is introduced.
This study points to an area of our map of cancer and labels a rather large chunk of it “terra incognita.” It makes the case that future research should try to chart that area.
The work “addresses the biologic complexity of cancer, informs future research efforts, and ultimately, might support improved risk assessment,” Gapstur said.