People who regularly drink from cans and plastic bottles may want to reconsider: A new study shows that a common chemical in the containers can seep into beverages and raise blood pressure within a few hours.
The research raises new concerns about the chemical bisphenol A, or BPA, which is widely found in plastic bottles, plastic packaging and the linings of food and beverage cans. Chronic exposure to BPA, as it is commonly known, has been associated with heart disease, cancer and other health problems. But the new study is among the first to show that a single exposure to the chemical can have a direct and fairly immediate impact on cardiovascular health.
The study found that when people drank soy milk from a can, the levels of BPA in their urine rose dramatically within two hours — and so did their blood pressure. But on days when they drank the same beverage from glass bottles, which don’t use BPA linings, there was no significant change in their BPA levels or blood pressure.
The findings suggest that for people who drink from multiple cans or plastic bottles every day, the repeated exposure over time could contribute to hypertension, said Dr Karin B Michels, an expert on BPA.
Dr Michels said the design of the new study was impressive and its findings “concerning”. “I think this is a very interesting and important study that adds to the concern about bisphenol A,” said Dr Michels, an associate professor at Harvard Medical School and Brigham and Women’s Hospital. “It raises a lot of questions. We have such a high rate of hypertension in this country, which has risen, and we haven’t really thought of bisphenol A and its use in cans as one of the causes of that. “
The chemical is an endocrine disrupter that can mimic estrogen. In 2012, the Food and Drug Administration said BPA could no longer be used in baby bottles and children’s drinking cups. Canadian regulators formally declared BPA a toxic substance in 2010 and banned it from all children’s products.
Not everyone is convinced that BPA poses a risk to consumers. The American Chemistry Council, an industry trade group, has said BPA is safe and has opposed federal and state legislative proposals to ban it.
Much of the evidence against BPA comes from large population studies rather than controlled clinical trials. A number have linked high urinary levels of BPA to a greater risk of hypertension and heart and peripheral artery disease. But those studies simply show correlations, and do not provide evidence that BPA is the cause.
The latest study, published in Hypertension, a journal of the American Heart Association, was a randomised controlled trial. The authors, a team from Seoul National University’s department of preventive medicine in Korea, recruited 60 older subjects, most of whom were women, and assigned them to drink soy milk from cans or glass bottles on three separate occasions, weeks apart. A majority had no history of high blood pressure, though some did.
The researchers chose soy milk because it does not have any properties that are known to increase blood pressure. And unlike soda, fruit juice and other acidic beverages, which are more likely to leach BPA from containers, soy milk is considered fairly neutral.
When the subjects drank from glass bottles, the study found, their urinary BPA levels remained fairly low. But within two hours of drinking from a can, their levels of BPA were about 16 times higher. As BPA levels rose, so too did systolic blood pressure readings — on average by about five millimetre of mercury. In general, every 20 millimetre increase in systolic blood pressure doubles the risk of cardiovascular disease.
BPA is known to block certain estrogen receptors that are thought responsible for repairing blood vessels and controlling blood pressure. It may also affect blood pressure indirectly by disrupting thyroid hormone.
“Clinicians and patients — particularly hypertension or cardiovascular disease patients – should be aware of the potential clinical problems for blood pressure elevation when consuming canned food and beverages,” said Dr Yun-Chul Hong, an author of the study and director of Institute of Environmental Medicine at Seoul National University.