Differential association of lead on length by zinc status in two-year old Mexican children

BACKGROUND Blood lead levels have decreased in Mexico since leaded fuel was banned in 1997, but other sources remain, including the use of lead-glazed ceramics for food storage and preparation. Zinc deficiency is present in almost 30% of children aged 1-2 years. Previous studies have documented negative associations of both lead exposure and zinc deficiency with stature, but have not considered the joint effects. Given that the prevalence of stunting in pre-school aged children was 13.6% in 2012, the aim of this study was to evaluate if the relationship between blood lead and child stature was modified by zinc status. METHODS Anthropometry, dietary energy intake, serum zinc and blood lead were measured in 291 children aged 24 months from an ongoing birth cohort study in Mexico City. Child stature was represented by recumbent length as appropriate for this age group. The association between blood lead (BPb) and length-for-age Z score (LAZ) was evaluated using a model stratified by zinc status measured by standard criteria and adjusted for: birth length, breastfeeding practices, energy intake, maternal height and education. RESULTS Median (IQR) BPb was: 0.17 (0.12-0.26) μmol/L and 17% of the sample had zinc deficiency (<9.9 μmol/L). BPb was inversely associated with LAZ in the overall sample (β = -0.19, p = 0.02). In stratified models, this negative association was more than three times higher and statistically significant only in the zinc deficient group (β = -0.43, p = 0.04) compared to the zinc replete group (β = -0.12, p = 0.22) (BPb*zinc status, p-for-interaction = 0.04). CONCLUSIONS Zinc adequacy is a key factor that may attenuate the negative association of lead on stature in young children.