Lead is a ubiquitous metal and its blood concentrations are considered the best indicator of human exposure. No BLLs are considered safe in children, who are particularly susceptible to lead poisoning [11, 12] because their organ systems are still developing. Lead exposure is often unrecognized because it typically occurs without obvious symptoms. BLLs in children aged ≤10 years ranged from 10.98 to 511.2 µg/L (mean: 135.59 µg/L) in Shenyang in the year 2000 [13]. In the present study, we found lower BLLs, perhaps as a result of the implementation of unleaded gasoline policies and relocation of heavy industries. However, child BLLs in China are still higher than in developed countries. The median BLLs in Korean children aged 3–5 years was reported as 13.4 µg/L in 2014 [14]. In Japan, the geometric mean of BLLs in 12-year-old children was 7.0 µg/L [15]. In New Zealand and Canada, the geometric means of BLLs were reported as 8.6 µg/L [16] and 9.7 µg/L [17], respectively.
Recent studies have shown that low-concentration lead exposure can also exert adverse effects on children [4, 6], but as lead exposure levels have declined, research into lead sources has tapered off. In the present study, we found that frequent hand washing was inversely associated with BLLs, perhaps indicating that dust was a source of lead and that washing it off hands prevented exposure by inhalation or ingestion [18]. Therefore, children should wash their hands frequently, especially before eating, to reduce absorption of substances such as metals and bacteria. Furthermore, we found that BLLs exceeding 50 µg/L were more common in younger children (aged 1–3 years), perhaps because they have not yet developed good hygiene habits and because they are more likely to put their hands into their mouths.
Food consumption is currently considered a major source of lead [7], but data on specific dietary sources of lead are inconsistent. We found that consumption of puffed grains was a risk factor for BLLs exceeding 20 µg/L, which was consistent with a previous report [19]. The main ingredients in puffed grain foods are starch, oil, and flavor additives, posing a further risk of overweight and obesity.
We also found an association between consumption of eggs and BLLs exceeding 20 µg/L, perhaps because environmental pollution increases lead content in eggs and lead absorption through the intestines increases with the number of eggs ingested. However, we did not found literature to support this view. Eggs contain a rich content of protein, and protein intake was reported to be a positive modulator of BLLs in humans [20]. Moreover, high-protein diets have been shown to increase lead absorption in rats [21]. Nonetheless, eggs are nutrient-rich foods that are easily accessible in low- and middle-income countries [22].
Previous studies have shown positive associations between consumption of grains and vegetables and BLLs, supporting the hypothesis that these foods are sources of lead [23–25]. Whole grains contain more dietary fiber than refined grains or vegetables, and dietary fiber can bind to lead and inhibit its gastrointestinal absorption [9, 26]. Other studies have reported that consumption of milk may also reduce lead uptake [27, 28], but we found associations with BLLs for only puffed grains and eggs, possibly reflecting geographic variations in dietary habits.
Our study had several limitations. First, this was a single-center study and some selection bias may be present; most data were collected by questionnaire and recall bias may be possible. Second, our study was cross-sectional and cannot infer a causal relationship. Third, the cohort was relatively small.
In conclusion, we found that BLLs of young children in Shenyang, China is gradually decreasing and that consumption of puffed grains and eggs is a source of lead. Frequent hand washing may be protective against high BLLs.