Previous studies showed that an empty stomach increases the absorption of lead and thus elevates B-Pb in adults, but it not clear if this effect exists in children as well. There have been no other studies directly quantifying the impact of regular breakfast consumption on lead absorption in children. In this analysis, we found that median B-Pb in those children who eat breakfast regularly was about 15% lower than that in children who do not eat breakfast regularly. This study provides important early evidence supporting the hypothesis that eating regular meals such as breakfast is associated with lower B-Pb in children. To our knowledge, this is the first human study exploring the association between breakfast frequency and B-Pb in young children. Eating frequent and regular meals (including breakfast) and snacks have been recommended by many health organizations for preventing and reducing lead poisoning in children, and these data concur. For example, the U.S. Advisory Committee on Childhood Lead Poisoning Prevention recommends that caregivers provide regular meals and snacks to young children [14
A number of studies have shown that food in the gastrointestinal tract reduces the absorption of ingested lead in adults [7
]. Experimental studies showed that the bioavailability of ingested lead in adults when taken with a meal was about 10 times lower than that when ingested after fasting [7
]. The smaller magnitude of the influence in children (15% change) may due to relatively lower lead exposure dose in children, observational study design, and the difference in the kinetics of lead between children and adults.
The mechanisms behind the impact of fasting on gastrointestinal tract absorption of lead are not well understood. Mineral micronutrients, especially the presence of calcium and phosphate in the intestinal lumen, may play a role by competing with lead for absorption [7
]. Epidemiologic studies have shown increasing dietary calcium intake is inversely associated with B-Pb in children [15
]. Higher dietary iron intake is also associated with lower B-Pb in the U.S. children[17
]. In the present study, however, we did not find significant associations between blood levels of these mineral micronutrients and B-Pb. We did find significantly higher blood levels of zinc in children who ate breakfast regularly, which may suggest that their dietary zinc intake was greater and perhaps competed with lead for absorption. Our analysis of dietary micronutrient intake in a subgroup of 270 children, however, did not suggest higher zinc intake in regular breakfast eaters. In previous studies, while some studies observed associations between dietary intake/supplementation (Ca, Fe, and Zn) and B-Pb [8
]others did not [11
]. In a study in the US, Gallicchio et al. did not found associations between B-Pb and daily micronutrient intakes (iron, calcium, vitamin C, or vitamin D) after controlling lead exposure and child's age [11
]. A clinical trial showed that Ca supplementation did not statistically significantly change B-Pb among children 1 to 6 years of age when B-Pb were 10- 45 μg/dL [24
]. There are two possible explanations for the inconsistency with this study. First, B-Pb are lower than those in previous studies. Second, children in this study are younger than the ones in previous studies.
The associations between socio-demographic factors and B-Pb found in previous studies were also observed in the present study [19
]. Some of these factors including age and gender are strongly associated with B-Pb, but not modifiable. Other factors including living area and parental education and occupation might not be possible to improve solely through public health intervention. Targeting children's breakfast consumption habits is relatively more feasible at both the family and community levels.
Several limitations must be considered when interpreting the findings from the present study. We have no data on the key variable of environmental lead exposure, a factor that might explain the higher B-Pb and greater risk of toxicity in older children if cumulative lead exposure increases over time. Clearly, our findings regarding increased B-Pb with increasing age merit repeated measures over time together with measures of environmental lead. We have information of dietary intake of micronutrients on only 270 of the larger sample of 1344 children, and thus cannot be certain that these micronutrient intake levels are representative of the entire group. Parental report of regular breakfast consumption in their children may lead to bias and misclassification. A guide was provided to parents to answer this question. However, for those children primarily living with their grandparents, the information may be less accurate. We did not ask parents the number of days the child ate breakfast during the week but instead used an arbitrary definition of "at least 5 days per week" as an indication of regular breakfast consumption. This was suggested by our local partners who believed that this would reasonably distinguish children. Second, the association observed in this cross-sectional study may not represent a causal relationship. There may be a tendency for higher B-Pb's to be associated with a decreased appetite for eating breakfast. Given the data collected from this study, we cannot determine to what extent appetite affected the reported breakfast consumption. Third, the lack of association in the multivariate logistic regression analysis on lead poisoning is likely due to the limited magnitude of nutritional influence at relative low exposure level [24
] and the small number of children with elevated B-Pb (7.9% for children with regular breakfast and 10.4% for children with irregular breakfast). Fourth, other potential confounders (e.g., household income and drinking water source) which were not assessed or included in the multiple regression models might contribute to the lower B-Pb observed among children who ate breakfast regularly. Finally, given the impact of fasting on lead absorption, regular breakfast is expected to modify the associations between external exposure levels and B-Pb which we cannot examine in this study due to lack of external exposure data.
Our findings, if replicated in future studies, have three practical implications. First, the importance of breakfast consumption as a strategy to increase meal frequency is suggested. Second, our data suggest that the risk of lead toxicity and higher B-Pb increases over time, a finding that suggests consideration of environmental routes of lead exposure. Third, we found that parental characteristics are major determinants of children's breakfast frequency. Children from families with higher parental education levels and technicians/professional workers are more likely to have regular breakfast. This indicates that parents play important role in increasing children's breakfast frequency which may in turn reduce B-Pb. Promotion of parents' and child care givers' awareness of the importance of breakfast as a proactive protective factor in reducing childhood B-Pb should become a part of all lead prevention programs. Because both lead exposure[1
] and malnutrition[34
]are related to children's negative cognitive and behavioral outcomes, promotion of regular breakfast in children can potentially enhance both physical and mental health well-being.