Yale School of Medicine researchers reported today that the chemical bisphenol-A (BPA), a building block for polycarbonate plastics found in common household items, causes the loss of connections between brain cells. This synaptic loss may cause memory/learning impairments and depression, according to study results published in the Proceedings of the National Academy of Sciences (PNAS).
Unlike previous studies that looked at the effect of BPA on rodents, the team examined the effects in a primate model. They also used lower levels of the chemical than in past studies. “Our goal was to more closely mimic the slow and continuous conditions under which humans would normally be exposed to BPA,” said study author Csaba Leranth, M.D., professor in the Department of Obstetrics, Gynecology & Reproductive Sciences and in Neurobiology at Yale. “As a result, this study is more indicative than past research of how BPA may actually affect humans.”
Over a 28-day period, Leranth and his team gave each primate 50 micrograms/kg of BPA per day, adjusted for body weight, the amount considered safe for human consumption by the Environmental Protection Agency (EPA). The team also administered estradiol, the major form of hormonal estrogen that modulates nerve cell connections in the brain. Best known as one of the principal hormone products of the ovary, estrogen has also been shown in past studies to be synthesized in the brain, where it aids the development and function of the hippocampus and prefrontal cortex.
The team then used an electron microscope to count nerve cell connections in the brain. They found that BPA inhibits creation of the synaptic connections in the hippocampus and prefrontal cortex, areas of the brain involved with regulation of mood and formation of memory.
“Our primate model indicates that BPA could negatively affect brain function in humans,” said study co-author Tibor Hajszan, M.D., associate research scientist in Yale Ob/Gyn. “Based on these new findings, we think the EPA may wish to consider lowering its ‘safe daily limit’ for human BPA consumption.”
Hajszan said that although daily exposure of an average person to BPA usually does not reach the level that was applied in this study, human exposure to BPA is not limited to a single month, but rather is continuous over a lifetime. “The negative effect of BPA may also be amplified when estradiol levels are naturally lower than in healthy adults. That is why exposure to BPA may particularly be risky in the case of babies and the elderly.”
Other authors on the study included Klara Szigeti-Buck, Jeremy Bober and Neil J. MacLusky.
The study was supported by the National Institutes of Health and by a National Alliance for Research on Schizophrenia and Depression Young Investigator Award.
Citation: PNAS Online Early Edition, 10.1073/pnas.0806139105 (September 2, 2008)