Experts conflicted on controversial caffeine–pregnancy study

The research in question, published in BMJ Evidence Based Medicine, suggests ‘there is no safe level of consumption’ and as such women who are pregnant or trying to conceive should avoid caffeine.
 
This finding is based on a meta-analysis of observational studies which, according to author Professor Jack James, shows maternal caffeine consumption is associated with negative pregnancy outcomes.
 
The University of Reykjavik psychology professor has previously made headlines for stating caffeine’s lethality is ‘underestimated’ and that it should be regulated like alcohol and cigarettes.

Current Australian guidelines indicate pregnant or breastfeeding women can consume up to 200 mg of caffeine per day, or roughly two cups of moderate-strength coffee.
 
However, Professor James said ‘substantial cumulative evidence’ of an association between maternal caffeine consumption and diverse negative pregnancy outcomes means current health recommendations are in need of ‘radical revision’.
 
‘Specifically, the cumulative scientific evidence supports pregnant women and women contemplating pregnancy being advised to avoid caffeine,’ he said.
 
Professor James delivered his recommendation despite conceding that the observational nature of the study means it cannot establish causation, and may be affected by other confounding factors, such as recollection of caffeine consumption, maternal cigarette smoking and pregnancy symptoms.
 
This conclusion has drawn a strong rebuke from a number of other researchers, including University of Adelaide reproductive epidemiologist Professor Michael Davies, who said it is ‘potentially alarmist’ as ‘the study extrapolates beyond available data’.
 
‘There is no clear evidence of harm at low levels of tea and coffee consumption, as there are no reliable data due to low observed risks,’ he said.
 
‘Maternal genes that control the metabolism of caffeine should be associated with adverse outcomes as they alter maternal and fetal exposure, but they are not. This implies a different unmeasured factor is involved.
 
‘Extreme levels of exposure to, or consumption of, any substance may well adversely alter fetal development. Please, moderation in all matters to protect the welfare of mother and child.’
 
Dr Alex Polyakov, a Senior Lecturer in the Department of Obstetrics and Gynaecology at the University of Melbourne, is also critical of the study’s findings and said there are ‘significant shortcomings’ involved in the analysis.
 
‘The article by Professor Jack James is not what one would call “original” or “primary” research ... all the studies included in the current analysis, with very few exceptions, were retrospective in nature,’ he said.
 
‘This means that in the majority of studies women were asked to recall their caffeine consumption before and during their pregnancy, often quite a long time after they have given birth or had an adverse outcome, such as miscarriage.
 
‘Such studies and the conclusions that they reach often suffer from what statisticians call “biases” … [and] there are numerous biases that make retrospective studies included in this review less accurate and their conclusions more suspect.’
 
Dr Polyakov added that confounding factors are another source of uncertainty, while the reliance on meta-analyses is ‘flawed’, as observational studies often focus on drastically different populations, interventions and outcomes, and are therefore are not ideal for this type of research.
 
However, he also stated that the study shows there is a ‘weak association’ between caffeine consumption and some adverse pregnancy outcomes.
 
‘The clinical significance of this association is unclear and, indeed, the causative link between the two has not been established,’ he said.
 
‘Nevertheless, the preponderance of evidence point towards caffeine consumption being a risk factor for miscarriage, low birth weight, and to a lesser extent stillbirth and childhood leukaemia.
 
‘The magnitude of this risk remains unclear, but is likely to be small and of questionable clinical significance.
 
‘It is worth noting that these risks appear to increase in a dose-dependent fashion, implying that higher caffeine consumption resulting in a higher risk. Therefore, the sensible approach would be to discourage women who are trying to conceive and those who are already pregnant from excessive and regular caffeine consumption.
 
‘It may be prudent to revise down [the] recommended amount [of 200 mg per day], to discourage pregnant women from daily caffeine consumption and to extend this revised advice to women who are trying to conceive.’
 
More researchers, including National Association of Specialist Obstetricians and Gynaecologists (NASOG) President, Associate Professor Gino Pecoraro, also questioned Professor James’ call to revise guidelines.
 
But others had less definitive responses.
 
The University of Newcastle’s Professor Clare Collins said the review is ‘timely’ and ‘should trigger greater caution [with regards] to caffeine in human pregnancy’, while Dr Cathy Knight-Agarwal from the University of Canberra’s School of Clinical Sciences believes the study provides some ‘compelling evidence to ponder’ despite its flaws.
 
‘From my perspective the only benefit of consuming such products is perhaps the psychological pleasure they induce,’ Dr Knight-Argawal said. ‘Which is all very well and good, but is this enough of a reason not to cease consumption during pregnancy?
 
‘The Australian and New Zealand governments advise women not to consume alcohol during pregnancy, as there is no established level of safety.
 
‘Perhaps caffeine intake advice during pregnancy should mirror that of alcohol? This is a topic for further debate.’
 
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