Women exposed to higher levels of the pesticide DDT while in utero face increased risk of breast cancer later in life than those exposed to lower levels, according to new research published in the US Journal of Clinical Endocrinology & Metabolism.

Researchers evaluated 54 years of data from women, including 9,300 tracked from even before birth. Of the number, the study’s authors identified 118 women who had been diagnosed with breast cancer. Those whose mothers had been exposed to significant levels of DDT in pregnancy were found four times more likely to contract breast cancer than those  exposed to a small quantity.

Study author Dr. Barbara Cohn, a researcher at the Public Health Institute in Berkeley, California, said the research found “direct evidence” that higher DDT exposure in utero places women at increased risk of breast cancer.

“Environmental chemicals have long been suspected causes of breast cancer, but until now, there have been few human studies to support this idea,” Cohn said.

DDT, one of the first known endocrine disruptors, has been banned in most Western countries since the 1970s. Still, the study’s authors point out that many potentially affected women born in that era are just reaching the age when they are at increased risk for breast cancer.

Despite this and other health risks linked to DDT, including Alzheimer’s disease, obesity, and kidney and ovarian diseases, some countries still use the chemical to fight malaria, the study points out.