Exposure to PCBs, even at everyday environmental levels, may affect women’s menstrual cycles, according to a new study.

The findings support animal studies suggesting that low-level exposure to PCBs (polychlorinated biphenyls) can alter menstrual function, lead investigator Dr. Glinda S. Cooper and colleagues report. Whether that translates into health effects, such as fertility problems, is unclear.

PCBs were once used in a wide range of industrial processes and consumer products, from plastics to household appliances to pesticides, but were banned in the U.S. in the late 1970s as a probable cancer risk.

However, PCBs linger in the environment and accumulate in the fatty tissue of animals, so exposure to the chemicals continues - mostly through diet, particularly consumption of contaminated fish.

Some PCBs are also believed to act as endocrine disrupters, meaning they affect the body’s hormonal system - though the possible health consequences to humans are not yet understood, Cooper explained to Reuter Health.

The new study, published in the journal Epidemiology, examined stored blood samples collected from more than 2,300 U.S. women in the 1960s.

Among the women in the study, who were all pregnant when their blood samples were drawn, those with higher blood PCB levels tended to have a history of slightly longer menstrual cycles - meaning more time between monthly periods. The difference in cycle length between women with the highest and lowest PCB levels amounted to less than one day.

Women with the highest PCB levels were also somewhat more likely to report having irregular periods.

The findings show that women’s menstrual cycles could serve as “sensitive markers” of the potential biological effects of endocrine disruptors, Cooper said.

Cooper, a researcher with the National Institute of Environmental Health Sciences in Durham, North Carolina, stressed that a “biological” effect is different from a “health” effect, such as infertility.

However, she added, “if we know something has the capability of influencing menstrual cycle characteristics, it provides a greater justification for examining that particular exposure in relation to specific health outcomes.”

PCBs have been shown to interfere with reproduction in animals, such as monkeys, leading to lower rates of conception and live births. Studies have also found lower birth weights among children born to women with high PCB exposure due to their jobs or heavy consumption of contaminated fish.

Research has pointed to several ways in which PCBs may disrupt the endocrine system, according to Cooper and her colleagues. Studies in animals and humans have suggested that PCBs may affect levels of thyroid hormone, which helps regulate metabolism. Excessively high or low thyroid levels are known to change women’s menstrual function.

There is also laboratory evidence that PCBs may increase levels of the reproductive hormone gonadotropin-releasing hormone, or be directly toxic to female egg cells.

However, Cooper and her colleagues write, “Which of these potential mechanisms, if any, is relevant to humans is unclear.”

SOURCE: Epidemiology, March 2005.