Drinking from glass bottles rather than cans may be better for your blood pressure, according to Korean researchers, although not everyone is convinced. The trial, which looked at whether bisphenol A (BPA) present in cans raises blood pressure, was performed by Dr Sanghyuk Bae and Professor Yun-Chul Hong of Seoul National University. Previous studies have found that BPA in the epoxy lining of cans may leach into foods in contact with it, the authors write in Hypertension. In this study the authors used a soy drink popular in Korea and available in cans or glass bottles, to test whether BPA affected blood pressure. “The reason we used the soy milk was that it has no known ingredients that elevate blood pressure,” says Hong. “Actually soy milk is known to reduce blood pressure,” he adds. Bae and Hong deliberately chose the soy drink for their clinical trial, involving 60 elderly people, because they expected BPA would raise blood pressure and they did not want to expose elderly participants to the risk of high blood pressure in the trial. “We chose elderly people because they are more susceptible to environmental exposure,” they said. The participants had to visit a community centre at 9am, after fasting for the preceding 8 hours. Their blood pressure was taken and then they were given two glasses of soy drink. The soy drinks were identical, but there were three ways the drink could have been packaged prior to serving: in two glass bottles; in two cans; or in one can and one bottle. Two hours later the participants’ blood pressure was measured again and a urine sample was taken. Each participant visited the community centre on three occasions, and so everyone consumed the soy drink from all three combinations of containers – a rigorous technique known as a ‘cross-over’ trial. The levels of BPA in the urine were 16 times higher when participants consumed soy drink from cans, compared to when they had the drink from glass bottles. It seemed BPA was indeed leaching into the soy. As expected, the participants’ blood pressure was lower after the soy drinks, presumably because of their blood pressure-lowering effect. The fall in blood pressure was 7.9 millimetres of mercury (mm Hg) after having the soy drink bought in glass bottles, but there was only a 2.9 mm Hg fall when the drink from two cans was consumed. Bae and Hong concluded that the BPA from the cans had caused a rise in blood pressure of about 5 mm Hg, partially counteracting the effect of the soy drink. But Professor Mark Nelson of Australia’s High Blood Pressure Research Council, who was not involved in the research, thinks that it is too big a leap to say that BPA causes a rise in blood pressure, when in fact measurements showed that blood pressure had declined. “Consuming these soy products reduces blood pressure. You saw that in all the groups. You saw less of it in the ones who consumed it from cans. The correct interpretation would be that consuming it out of cans, you don’t get all the benefit,” says Nelson. “I think they have shown that drinking from cans attenuates the blood pressure-lowering effect of the soy drink.” Professor Hong agrees that the experiments have not demonstrated that BPA is capable of pushing blood pressure above normal levels, but feels that this is a consequence of his ethical experimental design. So the jury is still out for drinks other than soy, but both Nelson and Hong agree that for soy drinks at least, it is better to drink from glass bottles than cans.
ABC Health News, 9 December 2014 ;http://www.abc.net.au/news/ ;