Women whose mothers had higher levels of DDT in their blood while pregnant were nearly four times more likely to develop breast cancer as adults, a new study finds.
The report provides one of the strongest links yet between exposure to DDT - still widely used globally - and cancer. It’s especially reliable because the researchers found 50-year-old blood samples to show how much DDT was in the pregnant women’s systems, rather than rely on possibly faulty memories or other indirect measurements.
“Environmental chemicals have long been suspected causes of breast cancer, but until now, there have been few human studies to support this idea,” said Barbara Cohn of the Public Health Institute in Berkeley, California, who worked on the study.
“This 54-year study is the first to provide direct evidence that chemical exposures for pregnant women may have lifelong consequences for their daughters' breast cancer risk.”
Breast cancer affects more than 200,000 women a year in the United States, and kills more than 40,000. Most cases are sporadic –- there’s no direct known cause. Obesity, poor diet and a lack of exercise are very strong factors, and there are some genetic mutations that greatly raise the risk.
“This 54-year study is the first to provide direct evidence that chemical exposures for pregnant women may have lifelong consequences for their daughters' breast cancer risk.”
And while women often fear that environmental contaminants may raise the risk, there are only a few studies that show chemicals do affect it. The chemicals in cigarette smoke are a known risk factor, as is the drug DES, used in the 1950s and 60s to prevent miscarriages.
One study showed that women who worked with certain cancer-causing solvents also have a higher risk. But no study has so strongly demonstrated that DDT can raise the risk.
“Currently no direct evidence links in utero dichlorodiphenyltrichloroethane (DDT) exposure to human breast cancer,” Cohn and colleagues wrote in their report, published in the Journal of Clinical Endocrinology and Metabolism.
If their findings hold true, the consequences could be far-reaching, they said.
“Many women were heavily exposed in utero during widespread DDT use in the 1960s. They are now reaching the age of heightened breast cancer risk,” Cohn’s team wrote.
“DDT exposure persists and use continues in Africa and Asia without clear knowledge of the consequences for the next generation.”
Cohn and her colleagues studied blood taken from women during more than 20,000 pregnancies from 1959 through 1967. They gave birth to 9,300 daughters during that time.
“Independent of a maternal history of breast cancer, elevated maternal (blood levels of DDT) significantly predicted a nearly four-fold increase in the daughter’s risk of breast cancer,” they wrote.
DDT was first used in the U.S. in 1945 to fight mosquitoes that carried diseases such as malaria. It was most heavily used in the 1950s and 60s, but use was phased out when it became clear the chemical was not just killing insects, but affecting birds and other wildlife. Most notoriously, it thinned eggshells and caused precipitous declines in populations of bald eagles, ospreys and song birds.
Rachel Carson wrote about the indiscriminate sue in her 1962 book “Silent Spring,” which helped spawn the environmental movement. DDT for agricultural use was banned in the U.S. in 1972.
“However, the women exposed most heavily while in utero during the 1960s are currently reaching the age of heightened breast cancer risk,” Cohn’s team wrote.
“Many women were heavily exposed in utero during widespread DDT use in the 1960s."
Jenny Singleton thinks she’s one of them.
“My mother had breast cancer about 20 years ago,” Singleton, a professor at Georgia Tech in Atlanta, told NBC News. “I had it five years ago, at age 48. I’m 53 today.”
She was born in 1961 in Oakland, California, and her mother was part of the group of women studied for the report.
“I thought for sure I’d have a BRCA gene mutation, so I did do the testing, but it was negative,” said Singleton, who said she was religious about getting mammograms after her mother’s diagnosis. Now she wonders about the DDT.
“I grew up in urban Oakland, but my mother grew up in Riverside where in those days was farm country with huge orange fields,” Singleton said. DDT would have almost certainly been widely used there.
Singleton has had limited surgery called lumpectomy to remove her breast cancer, radiation and she’s taking a pill called tamoxifen that’s been shown to greatly reduce the chances that cancer will come back.
The study doesn’t prove that DDT caused breast cancer. The team only measured DDT levels in blood taken from the mothers of 118 women diagnosed with breast cancer, and compared them to 354 women whose daughters did not.
Any association will have to be tested in larger studies. And it’s possible even if there is a risk, it could wane over time, Cohn points out. “The present study investigates breast cancer diagnosed before age 52 years. Thus, these results do not address DDT associations with breast cancer diagnosed at a later age,” they wrote.
They noted that one study done in Italy showed dioxin might raise breast cancer risk for 20 years, but then the risk fell after that.
But Cohn’s team is continuing their work. “Because we have concerns from animal studies that other chemicals, too, could have effect on future generations, we have begun some research on the third generation, some of whom have started having babies of their own,” Cohn said.
