The health impacts of environmental pollutants may vary depending on the timing of exposure, according to scientists speaking Dec. 7 at the NIEHS Environmental Health Sciences (EHS) FEST in Durham, North Carolina. In a plenary session titled “Exposures Across the Lifespan,” researchers explained that periods of rapid cell division and processes that are carefully controlled by hormones, such as those during pregnancy, are especially sensitive to external stressors.
Ami Zota, Sc.D., from George Washington University, described the Dutch winter famine of 1945 as a classic example of environmental sensitivity during the prenatal period, varying even by trimester of development. Fetuses in the first trimester during the famine grew into adults more likely to be obese, with a three-fold increase in risk of coronary heart disease. Fetuses in the second trimester had an increased risk of obstructive airway disease as adults, and those in the third trimester were more likely to have impaired glucose tolerance later in life. The concept that environmental conditions early in life can have lifelong health effects is known as the developmental origins of health and disease.
Puberty as a sensitive period
Karin Michels, Sc.D., Ph.D., of the University of California, Los Angeles, said puberty, a period of rapid growth of reproductive organs, is a very important time of sensitivity to environmental factors. Along with growth of tissues comes rapid cell divisions and the potential for DNA replication errors. The profound hormonal changes that occur during this time can be sensitive to interruption.
There is relatively little human data on health effects of environmental exposures during puberty, according to Michels. Her current studies include exposures during puberty to environmental pollutants such as butyl perfluorooctanoic acid (PFOA) and benzyl butyl phthalate (BBP), and their effects on breast composition and later risk of breast cancer. PFOA and BBP are considered endocrine disrupting chemicals (EDCs) because of their ability to mimic or interfere with hormones, which are part of the endocrine system.
Conceptual shift for environmental health science
The endocrine system is particularly sensitive to environmental chemicals for several reasons, said NIEHS Clinical Director Janet Hall, M.D. The endocrine system is extremely complex, with many interacting parts, multiple points of regulation, and sensitivity to low levels of hormones. Environmental pollutants are also often present at low levels, which were previously assumed to be safe.
“We used to think chemicals acted by overwhelming the body’s defenses,” Hall said. “But now we are seeing that chemicals can act like hormones and drugs to disrupt the control of development and function at very low doses. And these chemicals can have effects not only now, but also in the future.”
According to Hall, cancer, metabolic disorders, obesity, diabetes, and cardiovascular disease are all influenced by chemicals in the environment. She said that some of these chemicals are particularly bad actors, including phthalates used in plastics and fragrances, polychlorinated biphenyls used as electrical coolants, and polybrominated diphenyl ethers used as flame retardants.
Interventions to limit EDC exposures
An understanding of the long-term health effects of these exposures motivates prevention efforts, said Michels. She is currently working with the Silent Spring Institute on websites and blogs to educate adolescent girls about ways they can avoid EDCs.
During the discussion, Jose Cordero, M.D., of the University of Georgia, raised the issue of starting to address lifelong health disparities by reducing exposure to harmful chemicals before conception. Zota agreed that reducing preconception exposures is an important step, and she challenged scientists to think more about effective interventions.
“We devote a lot of resources to understanding the scope and precision of the problem, but don’t have a parallel effort to prevent exposures. Right now there are very few evidence-bases tips or strategies to offer,” said Zota.
(Virginia Guidry, Ph.D., is a technical writer and public information specialist in the NIEHS Office of Communications and Public Liaison, and a regular contributor to the Environmental Factor.)