A small US study of humans appears to reinforce animal results that suggest bisphenol A (BPA) may affect the body's insulin response to glucose, paving a possible route to type II diabetes.
Although epidemiological studies have suggested a correlation between BPA exposure and insulin resistance/type II diabetes, the effects have not been studied in a controlled way in humans.
An 'exploratory' study, led by Frederick vom Saal from the University of Missouri-Columbia, exposed healthy men and women to a single BPA dose at the reference or 'safe' level defined by the US EPA (50 micrograms BPA per kg body weight per day).
The test subjects avoided canned food and drink and minimised handling of cash till receipts for 48 hours before tests to reduce background BPA levels. On two separate testing days, they downed a drink containing ethanol and tonic water, one of which was laced with BPA.
After giving the participants a glucose tolerance test drink, the research team monitored blood samples for insulin and proteins. They also measured levels of glycated haemoglobin or HbA1c, which is created when glucose sticks to red blood cells. Medics use high levels as an indicator of high blood sugar levels and a risk of developing type II diabetes.
The researchers found a positive correlation between glycated haemoglobin levels and changes in the so-called insulinogenic index, which indicates insulin response, for BPA compared with controls. They suggest that BPA exposure at the selected dose may alter glucose-stimulated insulin response in humans.
They are clear that the results do not show that the effects of BPA are related to metabolic disease. Instead, the study is an "initial step" towards investigating whether exposure to oestrogen-like chemicals, including other bisphenols, could contribute to insulin resistance by triggering an innate insulin-resistance mechanism.
"From a regulatory perspective, identifying any physiological response in humans to BPA at the presumed 'safe' daily BPA dose would indicate that key assumptions in the regulatory process are incorrect," the researchers write in the Journal of the Endocrine Society.
In its BPA risk assessment published in 2015, the European Food Safety Authority's Panel on food contact materials, enzymes, flavourings and processing aids (CEF) reduced the tolerable daily intake (TDI) for BPA to a temporary level of 4 micrograms/kg body weight/day. Efsa is stil collecting information for re-evauation of BPA and its TDI.