Lead detoxifying effects of ascorbic acid among school going adolescents of Karachi: a cluster randomized control trail

Date of Award


Document Type


Degree Name

Master of Science in Epidemiology & Biostatistics (MSc Epidemiology & Biostats)


Community Health Sciences


Background Lead toxicity has been a major public health problem and public health concern globally. Once lead enters the body, it is excreted with difficulty. It deposits in bones, It slows down children physical, mental development and decreases hearing and vision, produces anemia and impairs heart, liver and kidney functions. The association of low blood lead levels (BLL) (<1011g/di) with many adverse outcomes shows that there are no safety margins for lead exposure and lead presence in human body. In spite of the elevated lead in blood among children in this part of the world (South Asia) i.e. > 70%, a few studies are conducted to explore the protective role of Vitamin C (Ascorbic acid) to reduce the elevated lead levels. Objectives The primary objective of this study was to assess the difference in the mean change in (BLL) before and after Ascorbic acid oral supplementation of 250 mg and 500 mg once a day, for 4 weeks, among the school going adolescent of Karachi. Methodology A cluster randomized control trial was conducted among school going adolescents (aged 13-18 years) in four towns of Karachi. Four clusters (schools) were selected randomly from commercial/industrial and residential areas of Karachi with two clusters within each area assigned randomly to either Ascorbic acid 250 mg or 500 mg group. A total of 8 clusters were randomized in the study. Blood lead levels were assessed at base line and then after four weeks of the intervention. Exposure assessment was done through a questionnaire at base line, whereas dietary intake of Vitamin C assessment was assessed through a Food Frequency Questionnaire (FFQ) at the end of the intervention. Results Ascorbic acid oral supplementation for four week resulted in significant decrease in BLL which was 3.2911g/di (p=0.001) in group A (500 mg), whereas, in group B (250 mg) this was 2.69 μg/dl (p= 0.002). However, the clustered adjusted difference between the two groups was 0.595 μg/dl that was not significant (p=0.81). However, in multiple linear regression after adjustment for clustering, baseline blood lead levels, chipping off of school paints and presence of garbage point near school were found significantly associated with decrease in blood lead levels. After controlling for these variables the mean decrease BLL among the group receiving 500 mg Ascorbic acid was 3.11 tg/dl (p=0.021) as compared to group B (250 mg) . It was found in the study that those who had higher baseline BLL achieved more decrease in BLL compared to those who had baseline BLL <10p g/dl. Conclusion Ascorbic acid oral supplementation in both doses is effective in decreasing BLL more than 2 μg/dl from the baseline. However, 500 mg is more effective in decreasing the BLL than 250 mg after controlling for factors affecting it. Use of 500 mg Vitamin C daily could be useful as convenient way of lowering blood lead levels in children and young adolescent living in urban settings. Funding This study was supported by The Pakistan Science Foundation (PSF) Project No. 51237 (PS) granted to Prof. Anwar-ul-Hassan Gilarii of Department of Biological Sciences, Aga Khan University and by the student grant from Department of Community Health Sciences, Aga Khan University Karachi. Trial Registration: Trial was registered with Australian New Zealand Clinical Trials Registry (ANZCTR).

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