EXPERT REACTION: Caffeine during pregnancy may not be a good idea

I have 6 points to make:

1. The press release is potentially alarmist as the study extrapolates beyond available data.
    
   The statement that there is “No lower threshold” is not the same as no evidence of harm.  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.
    
2. 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.
    
3. The results between coffee and tea are contradictory, indeed opposing, for leukaemia where tea consumption is protective. 
    
4. The author has previously acknowledged that coffee and tea drinkers have lower all-cause mortality, but they attributes this to the positive non-caffeine properties of coffee and tea.
    
5. Extreme levels of exposure to, or consumption of, any substance may well adversely alter fetal development. 
    
6. Please, moderation in all matters to protect the welfare of mother and child. 

This review of research on the relationship between pregnancy outcomes and total caffeine intake from tea, coffee, cola and energy drinks provides evidence that women should avoid caffeine in pregnancy. Results also warrant a review of guidelines on the amount of caffeine deemed safe for regular consumption by pregnant women. The author has summarised data from 37 separate observational studies and 17 meta-analyses published from 1998 to 2019. Overall results show substantial consistency across findings, with 32 studies reporting a higher risk for adverse pregnancy outcomes with higher caffeine intakes, while 10 studies reported equivocal results or no association. Of the meta-analyses, 14 found a risk of harm for higher maternal caffeine intakes, four meta-analyses reported greater risk of miscarriage, two meta-analyses reported higher risks for still-birth, five meta-analyses reported greater risk for low birth weight or small for gestational age and three meta-analyses reported greater risk for childhood leukaemia. The three meta-analyses conducted for pre-term birth did not consistently indicate higher risk. 

While you could discount these results because they are from observational studies and hence they cannot infer causation; or because of methodological weaknesses and limitations inherent in observational studies; or because case-control studies are more prone to recall bias, the finding of a dose-response relationship cannot be ignored. This means that the risk of adverse pregnancy outcomes increases in a stepwise manner as caffeine intakes increase and this should raise an alarm.

The reality is that it is not ethical to conduct randomised trials that administer caffeine in a double-blind manner to see whether caffeine causes harm in human pregnancy. Together with research from animal studies, which has shown that caffeine can disrupt embryo transport, development, implantation, placental function and increase pregnancy complications, this review should trigger greater caution in regard to caffeine in human pregnancy.

This review is also timely because intakes of barista-style coffee, which has a higher caffeine content compared to freeze-dried coffee powders, as well as energy drinks, have increased in many countries in recent decades. Women may be unaware of what their total caffeine intakes are relative to the 300 milligrams per day commonly recommended as an upper limit. Results from further research may help clarify whether small amounts of caffeine are associated with harm.

Caffeine is found in a number of food products that may be consumed by women in pregnancy such as coffee (both instant and espresso), tea, cola drinks, energy drinks and chocolate. Currently the Food Standards Australia and New Zealand recommend pregnant and breastfeeding women to consume no more than 200mg of caffeine each day from all sources (for example espresso on average contains 145mg caffeine per 50ml cup and milk chocolate 10mg caffeine per 50g bar).

The research presented here is observational in nature, so cannot establish causation. No study design can account for confounding factors (for example what the true intake of caffeine may be) in the way that a randomised control trial can. However, it would be unethical to conduct such a trial with caffeine in pregnancy as the exact level of intake to cause harm to the growing baby is still largely unknown. In addition, the level of intake to cause harm may be different from woman to woman as well as being dependent on the stage of pregnancy as well as health status.

Despite its observational design, the current study provides some compelling evidence to ponder. If pregnant women cut out caffeinated products from their diet would this compromise their nutritional status and the answer is a big no. Therefore, from my perspective the only benefit of consuming such products is perhaps the psychological pleasure they induce – 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.

Consumption of caffeine by pregnant women is exceptionally common with over 80 per cent of American women reporting daily caffeine use and over 90 per cent in some European centres. Therefore, any study  looking at adverse effects associated with consumption of caffeine during pregnancy is important and any potential new recommendations will affect a large number of women.

The significant limitations in the design of the paper, mean that while it is worthwhile discussing caffeine consumption with pregnant women, I’m not convinced that a total ban is warranted at this time.

This paper is a review of 48 previously published observational studies and meta-analyses. Its findings were not unanimous.

It is not a new piece of research specifically designed to answer the question of whether caffeine causes harm and what if any, level of consumption is safe.

Three quarters of the studies looked out, found caffeine exposure during pregnancy was associated with adverse outcomes while one quarter found no or inconclusive associations. 

The adverse events associated with caffeine consumption include miscarriage, stillbirth low birth weight and small the gestation will age as well as childhood acute leukaemia and childhood obesity. 

While three quarters of the included studies found support for association with low birth weight and childhood obesity, only  half of the four preterm birth studies found an association while another half showed no association.
The comments around leukaemia were based on six studies, only half of which reported association and another third reporting adverse effects when smoking was added to caffeine consumption. 

There was no association with preterm delivery and no study reported a threshold below which harm was absent.

The author's conclusion that all pregnant women and women contemplating pregnancy should avoid caffeine is overly alarmist and inconsistent with the evidence.

This report actually provides no new evidence on the topic, instead providing just one individual’s different perspective on existing evidence. It is true that previous studies have not confirmed a safe limit of caffeine intake during pregnancy, but this is very different to concluding that all levels of caffeine intake are harmful.

In fact, previous studies are relatively consistent in showing that small to moderate amounts of caffeine (< 200 – 300 mg day) are unlikely to harm the pregnancy. The main associations, and therefore concerns, with negative pregnancy outcomes relate to women consuming high amounts of caffeine each day.

Therefore, the current recommendations are and remain that women should limit caffeine intake where possible to less than 200-300 mg daily, but this is out of an abundance of caution rather than high-quality evidence.

There are so many dos and don'ts associated with pregnancy and the last thing we need is to cause unnecessary anxiety. At the end of the day, women should be reassured that caffeine can be consumed in moderation during pregnancy.