Peripheral iron levels in autism: "available evidence is inconsistent"

Another blogging day, another meta-analysis; this time on the topic of peripheral iron levels and autism (in children) as per the paper published by Ping-Tao Tseng and colleagues [1]. Similar to another recent post on research published by this group (see here), I declare some personal interest in this paper in my role as part of the authorship group. But yet again, I want to reassure readers that this won't influence my hopefully critical musings on the paper and topic.

So, peripheral iron levels in autism was the name of the meta-analysis game "including iron, ferritin, or transferrin." This on the basis that iron is "an essential element in child development" and, at the time of submission, "no meta-analysis has evaluated peripheral iron levels in children with ASD [autism spectrum disorder]." I might add that iron and autism has been a topic previously covered on this blog from various perspectives (see here and see here).

From a starting number of publications in the hundreds, some 25 articles were eventually included in the meta-analysis. The cumulative number of participants - those diagnosed with autism vs. those not diagnosed with autism - were in the hundreds (~1700 vs. ~1800 respectively) bearing in mind important factors such as different measures related to iron were being assessed and different 'sample sources' (serum, plasma, hair, etc) were noted in the various studies included.

Results: "Our meta-analysis suggested that levels of serum ferritin in the children diagnosed with ASD (n = 391, mean age = 5.4, mean female proportion = 32.6%) did not differ significantly compared with the children without ASD." A similar trend was also observed when it came to hair levels of iron and food iron intake. Other measures - serum iron, plasma iron, blood transferrin - saw too few publications to make any valued judgements but were generally indicative of no significant differences between autism and not-autism groupings.

Of course such analyses are based on the available evidence at the time of meta-analysis so one has to be a little cautious not to assume that such findings are gospel. I might also add that our results say nothing about the possibility of critical periods (during pregnancy for example) where there may be a higher requirement for suitable iron levels when it comes to brain development or other important biological processes. To once again quote: "Further studies are needed to investigate iron storage during fetal development in ASD to elucidate more about the role of iron in the pathogenesis of ASD."

But as things currently stand, there is little to say that iron is a really, really important variable when it comes to childhood autism...

And whilst we're on the topic of iron and meta-analyses, another paper from Tseng and colleagues [2] has also been published with ADHD (attention-deficit hyperactivity disorder) in mind (with another small contribution from yours truly). The conclusion: "Our results suggest that ADHD [attention-deficit hyperactivity disorder] is associated with lower serum ferritin levels and ID [iron deficiency]." Perhaps I'll come back to this other study some other time, and how ADHD overlapping in a not insignificant number of people with autism (see here) might be something important to consider.

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[1] Tseng P-T. et al. Peripheral iron levels in children with autism spectrum disorders vs controls: a systematic review and meta-analysis. Nutrition Research. 2018; 50: 44-52.

[2] Tseng P-T. et al. Peripheral iron levels in children with attention-deficit hyperactivity disorder: a systematic review and meta-analysis. Sci Reports. 2018; 8: 788.

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