Autism and excessive folate use in pregnancy
Within the last week there has been considerable media coverage of a study which potentially suggests there may be a link between excessive folic acid use in pregnancy and autism. Folic acid supplementation has of course long been recommended for use in pregnancy in the prevention of spina bifida (a condition where the spine does not develop properly) and other birth defects. Headlines have included ‘too much supplements during pregnancy may raise autism risk’ and ‘excessive folate use by pregnant women can increase risk for autism in children, study says’. These headlines will be nothing short of alarming for every prospective parent who reads them. But what is the science behind these headlines?
Well this is where it becomes a bit tricky. The study conducted at the John Hopkins Bloomberg School of Public Health has not actually been published yet. The researchers presented the findings of the study at the International Meeting for Autism Research on Friday last in Baltimore. The presentation was press released and this is the only available information on which to appraise the claims. This is not an unusual process of course in most disciplines. Researchers typically present their findings at conferences before submitting/completing the publication process. We have to be more careful though in interpreting findings at this stage – not only have they not been peer reviewed by other expert academics in the field but the information provided in a press release or conference abstract is scant in comparison to a full published journal article on the study.
Fortunately there has been some very sensible reporting about this study, particularly focusing on the stage of pre-publication and the information that is available to appraise the findings. The Independent ran coverage of the study with the headline ‘Scientists urge caution over alarmist claim of link between pregnancy folate and autism’. Even better still in their sub-headline they include the direct quote from an independent expert: ‘Without details of the analysis, or any theory of action this looks like low-grade evidence and, if not peer-reviewed, seems irresponsible’. The newspaper had sought out the opinion of two well established experts in the area of developmental disorders, both of whom had urged caution about the interpretation of the findings. This practice of including the opinions of independent experts in discussion of research findings has been something we have strongly advocated.
Looking at the press release it is very difficult to extract enough information to be satisfied about interpreting the study findings on face value. For example, the press release states that “The researchers found that if a new mother has a very high level of folate right after giving birth – more than four times what is considered adequate – the risk that her child will develop an autism spectrum disorder doubles”. The risk of something ‘doubling’ depends on what ‘doubling’ means. When there is a relatively low risk of something then the risk is still low after it ‘doubling’. In a post in our ‘top tips’ series on appraising risk we discussed a few examples of what this language actually means. One example was imagining that eating too many cupcakes increased the chance of someone suffering a certain type of cancer by 50%. This of course sounds like cupcake consumption is a major risk factor without the context to judge that properly. But if the risk of developing the cancer (without eating cupcakes) is only 0.2% for example, that means the increased risk is now 0.3% (a 50% increase on the no-cupcake 0.2% risk). In the case of this autism study, the authors refer to a baseline incidence of 1 in 68 births – 1.5%.
It is important to also note that the researchers are reporting a correlation or association between folate supplementation and autism, and not a causal link. Two variables may of course be related but the cause may be down to a completely independent third factor. The potential causes of autism are frequently discussed in the media. We have covered explanations from maternal anti-depressant use, C-Section birth, and siblings being born too close together. It is still worrying to see a lot of sensationalist headlines around an issue that could have serious negative effects on health outcomes, for example if a woman decided not to supplement with folate after reading these headlines. Fortunately most of the reporting was sensible urging caution about the findings and emphasising the importance of folate use for reducing neural tube defects.