In a letter to be published in this week's Journal of the American Medical Association (JAMA), Dr Stanley Young, assistant director of bioinformatics at the US National Institute of Statistical Sciences, and Ming Yu from the University of British Columbia, highlight the statistical limitations of the study from UK researchers.
The study, also published in JAMA last September by Dr Ian Lang and his colleagues, concluded that the 25 per cent of people with the highest levels of BPA in their bodies were more than twice as likely to have heart disease and, or diabetes compared to the 25 per cent of the people with the lowest levels.
However, Young and Yu maintain that Lang et al’s research did not adequately address the potential for multiple testing to result in a false positive result.
They claim that the CDC National Health and Nutrition Examination Survey 2003-2004 that was used in Lang et al's study measured 275 environmental chemicals and a wide range of health outcomes.
Young and Yu point out that with 32 possible health outcomes, including combinations, potentially associated with any of the 275 chemicals, along with confounders and statistical models, there could be as many as nine million statistical models available to analyze the data so the conclusions of the UK researchers on BPA can only be arbitrary.
In reaction to the Lang study last autumn, the European Food Safety Authority (EFSA) said that the research included no information on long term exposure to BPA which it said would be important “in order to establish a correlation between BPA and the development of the chronic medical conditions in question.”
BPA is used in certain packaging materials such as polycarbonates for baby food bottles. It is also used in epoxy resins for internal protective linings for canned food and metal lids.
Meanwhile, another study, published in this month’s issue of the Environmental Health Perspectives, claims the chemical can permanently affect reproductive hormones, resulting in early puberty and odd ovulation patterns.
Hormones vital for controlling reproduction were permanently changed in female rats exposed to BPA early in life, report the researchers based in Argentina.
The study claims to be the first to find long lasting hormonal changes when exposure to the chemical occurs after birth, during critical times of development.
The researchers said that two levels of BPA were tested, with female rats injected for 10 days starting from birth with either a high dose (10 micrograms per microlitre) or a low dose (1 microgram per microlitre).
They concluded that exposed rats at both doses showed earlier signs of puberty and abnormal pattern of ovulation cycle (or menstrual cycle in humans), with the animals showing decreased production of luteinizing hormone (LH), which is needed for both rats and women to ovulate.
The Food and Drug Administration (FDA) is set to update its Science Board in a public meeting next week regarding its continued assessment of BPA in FDA-regulated products, including food contact applications.
The FDA's handling of BPA has been criticised by scientists and US lawmakers.
Last year, the agency claimed the packaging chemical was safe at current levels in consumer products but it used industry-funded reports to support this assessment.
The scientific community argued that the FDA, in its review of the chemical, should have also included independent studies that have raised uncertainties regarding the potential effects of low dose exposure to BPA in humans, in particular infants.
In December, the agency said it was undertaking further research on BPA, which would include consideration of some of those studies.