Colder-to-warmer changes in children's blood lead concentrations are related to previous blood lead status: Results from a systematic review of prospective studies

ObjectiveTo estimate the extent of changes in mean BLLs from colder to warmer months, in children aged 1–5 years with different status of lead in colder months.MethodologyWe performed a systematic review using an in-house algorithm developed in MEDLINE, EMBASE, Web of Science, and CINHAL. Search was performed between November 2012 and July 2013, and data evaluation and extraction were subsequently conducted. The mean BLLs observed in the warmer months was divided by the one observed in the colder months to obtain the warmer-to-colder ratio (WCR). Study-specific WCRs were pooled using the fixed-effects method of Mantel–Haenszel to estimate the combined WCR.ResultsFrom 4040 papers initially identified, eight cohort studies were considered relevant for inclusion. The combined WCR was inversely related to the BLLs observed during colder months. The values were 1.25 (95% CI: 0.90–1.60), 1.06 (95% CI: 0.92–1.19), and 0.95 (95% CI: 0.51–1.39) for children showing baseline BLLs of <10 μg dL⁻¹, 10–20 μg dL⁻¹and ≥20 μg dL⁻¹, respectively. The combined WCR was influenced neither by children's age nor place/date of study.ConclusionThe extent of the summer increase in BLLs depends on the BLLs in the colder months.