Effect of the mother's consumption of traditional Chinese herbs on estimated infant daily intake of lead from breast milk

Abstract

Infant exposure to lead through breast milk is of special concern because breast milk is considered the best food source for infants under 6 months. In this study, a total of the mothers provided colostrum samples once in the early postpartum period, but only 16 of them provided breast milk weekly at 1–60 days postpartum. The geometric mean of lead concentrations in all colostrum samples (n=72) was 7.68±8.24 μg/L. The concentration of lead in the breast milk of the consumption group (the mothers who consumed traditional Chinese herbs) was 8.59±10.95 μg/L, a level significantly higher than the level of 6.84±2.68 μg/L found in the control group (mothers who did not consume traditional Chinese herbs). In the consumption group (n=9), the mean concentration of lead in the breast milk decreased with days postpartum, from 9.94 μg/L in colostrum to 2.34 μg/L in mature milk. We found the highest daily lead intake in infants at birth, and the level gradually decreased after the first month. We used an estimation of the hazard index (HI) to analyze the health risk of infants. In total, 5.7% (2 out of 35) of the HI estimates exceed 1.0 for the consumption group. In conclusion, the consumptions of traditional Chinese herbs by the mothers in this study significantly affected the body burden of lead in their infants.

Introduction

Traditional Chinese herbs have been used in Chinese society for thousands of years, and consequently many husbands and family members would like to use herbal remedies to keep pregnant women in good health. However, increasing numbers of cases of heavy metal (such as lead (Pb), arsenic (As), and mercury (Hg)) intoxication caused by traditional Chinese herbs have been reported (Chan et al., 1977, Lightfoote et al., 1977, Baker et al., 1985, Huxtable, 1990, Chan et al., 1993, Markowitz et al., 1994). For example, in Taiwan, a 5-month-old baby girl died due to long-term consumption of traditional Chinese herbs, Ba-Pao-NeHwang-San, with a lead level of 44,000 ppm (Chi et al., 1993). There also have been reports of Ayurvedic medications causing lead poisoning in children because of their contamination with lead. Traditional Chinese herbs may be harvested from contaminated soil, so contaminants of herbs can be responsible for unexpected toxicity (But, 1994). These cases have drawn public attention to the regulation and safety of traditional Chinese herbs. However, according to our best knowledge, there are only a few officially recommended upper limits to the levels of heavy metals in traditional Chinese herbs in the world (Uen, 1999).

Lead is neurotoxic and may cause mental deficiency, movement disorders, kidney dysfunction, and abnormal perception, especially during fetal growth and development. Recent studies indicate that lead exposure during the first 3 years of life has the most long-lasting and damaging effects (Pueschel et al., 1996). At this stage, children's developing brains are most vulnerable to lead exposure because children of this age have a less well developed barrier between the blood and the brain, allowing relatively more lead to pass into their developing brains. Also, studies have suggested that lead itself acts to disrupt this barrier (Finkelstein et al., 1998).

Women are chronically exposed to environmental lead since infancy, and they accumulate a significant bone lead burden into the child-bearing age. Maternal body burden and current exposure are major lead sources for the fetus, because lead can pass through the placenta (Ellenhorn, 1997). Breast milk is the first food for infants and it serves as the major nutrient source for biological functions and growth during the early stages of life. There are some data on infant blood lead levels in relation to breast milk lead. Ryu et al. (1985) found a strong correlation between lead concentrations in the breast milk and the corresponding blood lead concentrations of infants until 6 months of age (r=0.42, p<0.0003), before infants begin to crawl and walk. In rats, Bogden et al. (1991) found that lead exposure during pregnancy could retard fetal growth and development, especially if the maternal diet during pregnancy was low in calcium. Gulson et al. (1998) assumed that there was no contribution from environmental samples such as house dust and ambient air. The contribution of lead in the breast milk as the only dietary source to the blood lead level of newborns was estimated from lead isotopic measurements to be in the range of 40–65% (Gulson et al., 1998). Therefore breast-feeding constitutes a major source of exposure to bioaccumulated contaminants for infants.

In Taiwan, little information is available on the association between consumption of traditional Chinese herbs and lead concentrations of breast milk. In this study, we examined the relationship between lead concentrations in breast milk and the consumption of traditional Chinese herbs commonly used during pregnancy and lactation. In order to assess the lead exposure in breastfeeding infants, we calculated and validated a hazard index to evaluate the impact of consumption of traditional Chinese herbs in infants in Taiwan.