Relation of Iron and Zinc to Child Cognition and Behavior Problems:

Moderation by Permissive Parenting and Lead Concentration

Laura Hubbs-Tait, Afework Mulugeta, Alemtsehay Bogale, D’Lee Babb, Tay S.

Kennedy, Tesfaye Wogene, Eric R. Baker, Barbara J. Stoecker

Rationale• Iron and zinc are linked to child cognition and

behavior. • Some studies report stronger associations

than others of these metals with child cognitive and behavioral functioning.

• One hypothesis for the inconsistencies is that effects of micronutrient deficiencies may be exacerbated or mitigated by parenting practices and neurotoxicant exposures (Hubbs-Tait, Nation, Krebs, & Bellinger, 2005).

Placing research on iron and zinc in context of risk

Micronutrients

Neurotoxicants

Social Environments

Child Cognition and Behavior

Hubbs-Tait, L., Nation, J. R., Krebs, N. F., & Bellinger, D. C. (2005). Neurotoxicants, micronutrients, and social environments: individual and combined effects on children's development. Psychological Science in the Public Interest, 6, 57-121.

Background - Iron• Circulating iron - hemoglobin (hgb)

– Hgb < age-appropriate value is indicative of iron deficiency• Preschool children: hemoglobin <111 grams per liter

[g/L] (CDC, 1998).

• Tissue iron– Measured by soluble transferrin receptors in

serum • increase with decreasing tissue iron • less affected by infection than ferritin • > 8.4 mg/L is cutoff for tissue iron deficiency

(Schneider et al., 2008)

Background - Zinc

• Less agreement on what constitutes zinc deficiency

• Previously (Droke et al., 2006) we used a nonfasting low zinc cutoff of 71.2 μg/dL for 3- to 5-year-old children

Neurotransmitters as conceptual framework

• Lower iron or zinc and higher lead affect glutamatergic functioning. – Lead causes changes in glutamate receptor, N-methyl-

D-aspartate (NMDA), in hippocampus • ↓ licking and grooming by rat dams causes

– Impaired rat pup learning and memory– ↓ NMDA receptor mRNA expression and synaptogenesis

• Zinc = essential ion for zinc finger protein (ZFP) structure found in neuronal receptors like NMDA and functions as an NMDA inhibitor.

• In vitro and in vivo research (Basha et al., 2003) shows zinc supplementation provided some protection against changes induced by lead in DNA binding of ZFP

Parenting Moderates Effects of Iron

• Cognitive hypothesisLevitsky and Barnes (1972) confirmed a hypothesis proposed by Frankova that environmental isolation exacerbated the effects of early malnutrition in rats. Rats were randomly assigned to both nutritional (malnutrition versus control) and environmental (isolation versus stimulation versus control) conditions.

Permissive parenting would exacerbate lower iron or zinc

• Behavior problems hypothesis

Zinc would be inversely related to behavior problems for children with lead levels > 2.5 μg/dL

Lead Moderates Effects of Iron and Zinc

Hubbs-Tait et al (2009) found that children with lead levels > 2.5 μg/dL had significantly lower perceptual subscale scores on the McCarthy Scales of Children’s Abilities than children with lead levels < 2.5 μg/dL. Thus, lead level > 2.5 μg/dL constitutes the additional risk.

Zinc has previously been reported to be inversely correlated with anxiety or other behavior problems, but usually under circumstances of greater micronutrient deprivation or other risk factors.

• PARTICIPANTS– 112 children (mean age = 4.15 ± .55 yr) in Head

Start – Exclusion criteria reduced total sample of 131

children who provided assent• blood lead level above 10 μg/dL (n =1)• insufficient blood sampled to measure lead or

transferrin receptors (n =5)• or C-reactive protein > 10 mg/L indicating

infection rendering measurement of nutritional biomarkers questionable or inaccurate (n = 13) (Thurnham et al., 2005; Droke, Kennedy, Hubbs-Tait, 2006).

METHOD

METHOD• Procedure

– Blood sampling – during a 3-week period in November 2006.

– Children completed the McCarthy Scales of Children’s Abilities (MSCA) and Peabody Picture Vocabulary Test – III (PPVT-III) prior to blood sampling.

– Parents completed questionnaires at Head Start centers or home.

– Teachers completed rating scales at Head Start centers.

METHOD• Measures

– Peabody Picture Vocabulary Test – III (PPVT-III)– McCarthy Scales of Children’s Abilities (MSCA)– Passive-permissive parenting: Parent Behavior

Questionnaire-Head Start (PBQ-HS, Coolahan, McWayne, Fantuzzo, & Grim, 2002)

– “I find it difficult to discipline my child” – “I have a hard time saying "no" to my child” – “My family says I spoil my child” – “When my child doesn't do what I ask, I let it go or do it myself”– “I tell my child I'll punish them but don't do it” – “If my child resists going to bed, I let them stay up” – “When I want my child to stop doing something, I ask many

times.”

– Cronbach’s α for original 11-item scale = .77; for our reduced permissive parenting scale in the current sample, α = .76.

METHOD• Measures (cont’d)

– Home literacy items by Senchal et al. (1996)• “Please estimate the number of children’s

books in your home” – response choices: 0 (none), 1 (1-5), 2 (2-10), 3

(11-15), 4 (16-20), 5 (21-25), and 6 (more than 25)• “How often does your child go to the library?”

– response choices of 1 (never), 2 (not often), 3 (sometimes), 4 (often), and 5 (very often)

– Teacher ratings• Preschool Behavior Questionnaire (PBQ,

Behar, 1977): anxious, aggressive, hyperactive• Sociable subscale of Howes (1988) teacher

rating scale

RESULTSHemoglobin: 8 children <111 g/LTransferrin receptors: 57 children > 8.4 mg/LFerritin: 38 < 15 ng/mLZinc: 6 < 71.2 μg/dL

1 child with low levels of all iron measures: Hgb < 111 g/L + ferritin < 15 and sTfR > 8.4 21 children with low ferritin and sTfR: ferritin < 15 and sTfR > 8.4

Permissive parenting scores of 22 Fe deficient children versus 79 sufficient children:

Low Fe 1.73 (.45)

Normal Fe 1.72 (.47) F (1, 99) = .016, p = .899

COGNITIVE RESULTS

T receptors Zinc Books Library Permissiv HS grad Income PPVT M Verbal

Transferrin receptors

Zinc .081

Books in the home -.083 .047

Child goes to library .124 .010 .203*Permissive parenting -.216* -.212* .013 -.053High school graduate -.071 .003 .197* .021 -.103

Household income .013 .041 .258** -.086 -.089 .040

PPVT-III -.320*** .044 .321*** .268** .086 .101 .161

MSCA Verbal -.210* -.119 368*** .213* -.044 .182 .122 .710***

MSCA Perceptual -.029 -.044 .239* .294** -.159 .040 .148 .330*** .445***

Relation of iron and zinc to child cognitive outcomes

Outcome Model Summary Coefficientsa

Block and Predictors R2 df p b SE p

MSCA Verbal

Home Environment .170 3, 95 .000

High school graduate .117 2.691 2.194 .223

Children’s books in home .315 1.954 .604 .002

Child library visits .150 1.498 .951 .119

Transferrin Receptors .048 1, 94 .018 -.224 -.129 .053 .018

PPVT-III

Home Environment .146 2, 96 .001

Children’s books in home .279 2.415 .835 .005

Child library visits .210 2.926 1.339 .031

Transferrin Receptors .097 1, 95 .001 -.316 -.254 .073 .001

COGNITIVE: Hierarchical regressions

COGNITIVE RESULTSHypothesis 1: permissive parenting would exacerbate lower iron

PPVT-III

Transferrin receptors

Low Permissive, b = -.766

High Permissive, b = - 4.427**

** p < .01

BEHAVIOR PROBLEMS

n = 77n = 28

Lead > 2.5 μg/dL Lead < 2.5 μg/dL

Hypothesis 2: Inverse relation for iron and zinc to behavior problems above lead threshold of 2.5 μg/dL

BEHAVIOR PROBLEMS

Lead > 2.5 μg/dL Lead < 2.5 μg/dL

n = 28 n = 77

CONCLUSIONS

Permissive parenting exacerbated the negative effects of lower iron.

Limitations include correlational design and reliance on parental self-report of styles and behaviors.

Lead level of 2.5 μg/dL did differentiate relations between micronutrients and teacher reports of behavior problems or social behavior.

Significant interactions involving micronutrients were found among relatively well-nourished US preschool children emphasizing importance of interdisciplinary designs.

Acknowledgements and Funding

ACKNOWLEDGMENT• I thank Brandy Simmons, Michelle Dickerson,

Katey Masri, Rachel Bonnett, Nicole Moore, Beatrice Okwonga, Emily McKenzie, Stephanie Chrisman, Brittany Overstreet, Amber Shelledy, Kelly Shipman, and Allison Fallis for assistance; and the parents and children for their involvement.

FUNDING: • United States Department of Agriculture-CREES,

Oklahoma Agriculture Experiment Station. USDA-CREES Number OKL0 2605.

THANK YOU!You may access these slides at the following address:

http://ches.okstate.edu/facultystaff/faculty-documents.php?FacID=24

RESULTS

Measure Total Sample (n=112)

Questionnaire Data (n=102)

No Questionnaire Data (n=10)

CRP elevation (n=13)

Mean (SD) Mean (SD) Mean (SD) Mean (SD)

PPVT-III 87.01 (13.86) 87.24 (14.06) 84.70 (12.00) 90.54 ( 8.80)

MSCA-Verbal 43.39 (10.32) 43.63 (10.25) 41.00 (11.23) 49.38 (11.24)

MSCA-Perceptual 44.88 (9.15) 45.47 (9.08) 38.90 ( 7.96) 48.15 (11.88)

Books in home 4.46 (1.62) 4.46 (1.62) missing 5.22 (1.39)

Library visits 2.28 (1.00) 2.28 (1.00) missing 2.60 (1.17)

Permissive parenting

1.72 (.47) 1.72 (.47) missing 1.54 (.41)

Lead μg/dL 2.10 (1.16) 2.09 (1.15) 2.22 (1.32) 2.35 (1.09)

Transferrin receptors mg/L

8.71 (1.71) 8.70 (1.77) 8.77 (1.02) 8.98 (2.78)

Zincb μg/dL 95.39 (15.52) 95.11 (15.91) 98.30(10.90) 94.15 (21.93)