Thursday, 17 July 2014

Blood lead levels and childhood behaviour

"Blood lead concentrations, even at a mean concentration of 6.4 µg/dL, were associated with increased risk of behavioral problems in Chinese preschool children, including internalizing and pervasive developmental problems". That was the conclusion of the study by Jianghong Liu and colleagues [1] looking at blood lead levels in preschoolers aged 3-5 years resident in Jiangsu province in China. Some associated media accompanying this study can be viewed here including the text: "This research focused on lower blood lead levels than most other studies and adds more evidence that there is no safe lead level".
You lead... @ Wikipedia 

Lead (Pb) is a metal which has appeared before on this blog - quite a few times in fact (see here and see here for example) - all for the wrong reasons. Outside of it's many and varied industrial uses, including helping many of us get from A to B, lead is pretty dangerous stuff if it manages to find itself into the human and animal body in any amount particularly with its neurotoxic effects [2] in mind.

For quite a few years, much of the guidance on exposure to lead had suggested that blood lead levels above 10 μg/dL "should prompt public health actions" [3] albeit not defining "a threshold for the harmful effects of lead". As per that CDC report [3] there has been an increasing realisation that even blood lead levels below 10 microg/dL may have some undesirable effects particularly on infants and young children. Indeed the revised CDC guidance now lists "5 micrograms per deciliter of lead in blood" as the point where concerns should be raised about blood lead levels and action taken.

Back to the Liu paper...

  • Looking at spot blood lead levels (BLLs) or even blood lead concentrations for over 1300 youngsters, researchers administered the "Chinese versions of the Child Behavior Checklist and Caregiver-Teacher Report Form" to parents and teachers of participants when children were aged 6 years old.
  • Results: the mean (average) BLL for participants was 6.4 µg/dL, although a range of results were reported. Incremental increases in BLLs correlated with an "increase of teacher-reported behavior scores on emotional reactivity, anxiety problems, and pervasive developmental problems". Also: "mean teacher-reported behavior scores increased with blood lead concentrations, particularly for older girls".
  • The authors conclude: "continued monitoring of blood lead concentrations, as well as clinical assessments of mental behavior during regular pediatric visits, may be warranted".

Bearing in mind this was a study looking at parent and teacher scoring of Chinese children and not more formal assessment of behavioural (or cognitive) issues, also focused on spot samples rather than multiple samples to assess BLLs, there are some important lessons to be learned from these results. Not least is the continued undesirability of contact with lead and it's potential effects on behaviour. I think back to some of the chatter on lead exposure and crime (see here) taking into account the old 'correlation is not the same as causation' mantra as one potential societal effect.

Reading through some of the other literature in this area, it's not difficult to find supporting information about the detrimental effects of lead exposure particularly in children. The paper by Hou and colleagues [4] (open-access here) pretty much sums it up: "Compared with healthy children, more children with lead poisoning had abnormal behaviors, especially social withdrawal, depression, and atypical body movements, aggressions and destruction". They conclude: "Lead is a neurotoxin with no physiological functions in the human body, the ideal concentration of which in the blood is zero".

Whilst exposure to lead through older formulations of petrol or house paint or plumbing is a declining issue in many areas of the world, I don't think we can be complacent about our situation. Roberts and colleagues [5] commented on this issue in their study (bearing in mind their use of the 10 microg/dL cutoff level). They noted: "Despite a low prevalence of children with EBLL [elevated blood lead levels], parental report suggested that approximately 29% of children had lead-based paint in their home environment". Similar analyses of other areas of lead exposure risk such as dust, soil and water suggest continued monitoring is required as per the study results from Oulhote and colleagues [6].

If there is a take-home message from this post and the Liu results it is that lead exposure can have often pronounced developmental effects on behaviour (and cognition) in infants and children and that even markers of low levels of exposure should be examined with much greater assiduity. Without trying to brush everyone with autism as lead poisoned, such results might also direct much greater research attention when findings of EBLL are noted in cases of autism (see here). Indeed, papers like the one from El-Ansary and colleagues [7] might offer much more information than they have hitherto been given credit for...

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[1] Liu J. et al. Blood Lead Concentrations and Children’s Behavioral and Emotional Problems. JAMA Pediatrics. 2014. June 30.

[2] Lidsky TI. & Schneider JS. Lead neurotoxicity in children: basic mechanisms and clinical correlates. Brain. 2003; 126: 5-19.

[3] CDC. nterpreting and managing blood lead levels < 10 microg/dL in children and reducing childhood exposures to lead: recommendations of CDC's Advisory Committee on Childhood Lead Poisoning Prevention. MMWR Recomm Rep. 2007 Nov 2;56(RR-8):1-16.

[4] Hou S. et al. A clinical study of the effects of lead poisoning on the intelligence and neurobehavioral abilities of children. Theor Biol Med Model. 2013 Feb 18;10:13.

[5] Roberts JR. et al. Are children still at risk for lead poisoning? Clin Pediatr (Phila). 2013 Feb;52(2):125-30.

[6] Oulhote Y. et al. mplications of different residential lead standards on children's blood lead levels in France: predictions based on a national cross-sectional survey. Int J Hyg Environ Health. 2013 Nov;216(6):743-50.

[7] El-Ansary AK. et al. Relationship between chronic lead toxicity and plasma neurotransmitters in autistic patients from Saudi Arabia. Clin Biochem. 2011 Sep;44(13):1116-20.

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ResearchBlogging.org Liu, J., Liu, X., Wang, W., McCauley, L., Pinto-Martin, J., Wang, Y., Li, L., Yan, C., & Rogan, W. (2014). Blood Lead Concentrations and Children’s Behavioral and Emotional Problems JAMA Pediatrics DOI: 10.1001/jamapediatrics.2014.332