May 20, 2019

expert reaction to conference abstract looking at phthalate exposure and markers of impaired liver function

Research being presented at the European Congress of Endocrinology suggests that exposure to common every day chemicals may increase the risk of metabolic disorders such as obesity and diabetes.

Prof Richard Sharpe, member of the Society for Endocrinology and Honorary Professor at the MRC Centre for Reproductive Health, University of Edinburgh, said:

“Numerous epidemiological studies have investigated the association between various aspects of metabolic function/obesity/liver function and exposure to various phthalates.  The results have been inconsistent and nothing in this small new study alters this.

“Another factor to keep in mind is that, at least for MEHP and its parent phthalate DEHP, human exposure is predominantly via diet (especially a modern Western diet), which is a huge confounding factor in such studies.  Finally, association does not prove effect, contrary to what the abstract of this study implies.”

Prof Rob Chilcott, Professor of Toxicology, University of Hertfordshire, said:

“The abstract simply does not provide sufficient information to support its conclusions.”

Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“It’s much too early to be concerned about this piece of research.  There are just too many questions about it, to which we don’t yet have answers.  How were the participants chosen?  Beyond knowing that they were volunteers, we aren’t told.  Are they typical of any wider population?  Were appropriate statistical methods used?  It seems that many statistical tests were carried out, and we aren’t told whether statistical adjustments were made to allow for this, as they should have been.  How did the researchers deal with the problems arising from this being an observational study?  There are likely to be many differences between the people with different concentrations of phthalates in their urine, apart from the difference in phthalates.  It’s possible that one or more of these other differences is the cause of differences in liver function, cholesterol levels and so on, and not the phthalate levels at all.  Likewise, there are likely to be considerable differences between obese participants, those with diabetes, and healthy control participants apart from differences in their phthalate concentrations.  Statistical adjustments can be made to allow to some extent for these issues, but again we don’t yet know whether or how these adjustments were made.  Even if they were made, that can’t allow for everything relevant, so it’s impossible to know clearly what causes what.

“So far we have only a press release and a brief abstract.  Already the press release goes beyond the abstract in saying that phthalates “may increase the risk of metabolic disorders” – the abstract doesn’t go further than saying that “exposure to phthalates may be related to the impairment of normal liver function”, which (rightly) says nothing about what causes what.  The research hasn’t yet been peer reviewed, so other scientists haven’t had the chance to check out the details and possibly answer some of my questions.  People at the conference where this is presented are unlikely to find out all the important details either, since it’s a poster presentation and you cannot get much information on a conference poster.  Even if the research does eventually get through peer review, the observational nature of the research means that we still can’t be at all confident about whether the phthalate exposure is causing anything in people like these.”

Abstract title: ‘Can phthalates impair liver function?’ by Milica Medic-Stojanoska et al.  This is a conference abstract from the European Congress of Endocrinology in Lyon, and is under embargo until 23:01 UK time on Monday 20 May 2019.There is no paper as this is not published work.

Declared interests

Prof Rob Chilcott: “None.”

Prof Kevin McConway: “Prof McConway is a member of the SMC Advisory Committee, but his quote above is in his capacity as a professional statistician.”

None others received.