(Reuters Health) - The once-common pesticide DDT has long been linked to an increased risk of breast cancer. Now, research suggests that women’s age at first exposure to DDT may influence when in life the risk for breast malignancies is greatest.

Women exposed to DDT before age 14, particularly in infancy and early childhood, were most likely to develop breast cancer, before age 50 and before they went through menopause, researchers report in the Journal of the National Cancer Institute. However, women exposed to DDT after infancy had a greater risk of developing cancer later, at ages 50 to 54.

In both groups, there was roughly a 40-year lag between first exposure and the window for increased risk of a breast cancer diagnosis, the study team notes.

“All women, regardless of age at first exposure, show a DDT connection to risk of breast cancer when considering diagnoses through age 54,” said lead study author Barbara Cohn of the Public Health Institute’s Child Health and Development Studies in Berkeley, California.

“Nearly everyone alive has been exposed to this very persistent chemical, particularly women currently being diagnosed with breast cancer through early post-menopause who were alive in the 1950s and 1960s before DDT was banned in many countries,” Cohn said by email.

DDT was hard to avoid before it was banned because it was sprayed from trucks and airplanes, and women came in contact with it through dust and food. The chemical is still sprayed in Africa to control malaria, although it has been banned in the U.S. since the early 1970s.

The U.S. Environmental Protection Agency lists DDT as a probable carcinogen, but previous research has been mixed about the link to breast cancer.

In the current study, women exposed to DDT before age 3 had an elevated risk of premenopausal breast cancer.

Women exposed to DDT from ages 3 to 13, meanwhile, had an elevated risk of breast cancer both before and after menopause, although the risk was stronger for diagnoses before age 50.

And women exposed to DDT after age 13, and after puberty, had an elevated risk of breast cancer after age 50, but not earlier.

The study followed 15,528 women over nearly six decades, tracking age at first DDT exposure, DDT levels during pregnancy and age when any breast cancers were diagnosed.

To determine levels of DDT exposure, the researchers analyzed stored blood samples that had been collected from 1959 to 1967 during pregnancy at each trimester and again shortly after delivery.

Researchers then used state records to identify 153 cases of breast cancer diagnosed from 1970 to 2010 in women age 50-54. They matched each of these cases with a control group of similar women who did not develop cancer.

“We don’t know exactly how DDT can cause breast cancer, but we do know that it is an endocrine disruptor,” said Julia Brody of the Silent Spring Institute in Newton, Massachusetts, who wasn’t involved in the study.

“Endocrine disrupting compounds (EDCs) are chemicals that scramble the body’s hormone signaling system, which controls growth and many other processes,” and are linked to many cancers, Brody said by email.

While few women born before DDT was banned could have avoided exposure, they can still take steps to minimize their risk of breast cancer, said Steven Coughlin, a researcher at Augusta University in Georgia who wasn’t involved in the study.

“To reduce their risk of breast cancer, women should remain physically active (150 minutes per week of moderate intensity physical activity), avoid cigarette smoking and minimize their consumption of alcohol,” Coughlin said by email. “Eating a healthy diet with plenty of fruits and vegetables and whole grains is also recommended.”

SOURCE: bit.ly/2Cib0Tq Journal of the National Cancer Institute, online February 13, 2019.