Lead in breast milk

Fact sheet for medical professionals

Brian L. Gulson, Graduate School of the Environment,
Macquarie University, Sydney NSW 2109

Owing to its unique nutritional and immunological characteristics, human milk is the most important food source for infants. Breast milk can, however, also be a pathway of maternal excretion of toxic elements such as lead.

These toxic substances impact most severely on the newly born at a time of rapid development of the central nervous system (Astrup-Jensen and Slorach, 1991). Apart from contributions from maternal sources during pregnancy such as from the skeleton (Gulson et al., 1997, 1998), other potential lead sources for the infant are mainly dietary, that is, from breast milk, infant formulae and baby foods.

Recently, Gulson et al. (1998) showed that there was an increased and sustained mobilization of maternal skeletal lead during lactation compared with during pregnancy, from which arises the question: Are the infants at more risk from breast feeding than from formula feeding? 

Table 1. Lead Concentrations in Breast Milk

How much lead is in breast milk?

The literature is rather cloudy on this issue partly due to the extremely large range in reported lead concentrations in breast milk.

Most of the data for the past 15 years are shown in Table 1. The very high levels reported in some papers are probably due to contamination of the milk during sampling and analysis (e.g. the Austrian and Italian studies). All units for breast milk are standardised to parts per billion (ppb). Note that in the United Arab Emirates, over 94% of the sample used Kohl (lead-bearing) cosmetics.

There is a linear relationship between lead in breast milk and in the mother’s blood so that, for example, in the 1993 Mexico study, the maximum blood lead was 99 µg/dL (compared with the U.S. Centers for Disease Control "Level of Concern" of 10 µg/dL) and for breast milk was 3.5 µg/dL or 35 parts per billion (mean 2.47 µg/dL) compared to the allowable level of lead in drinking water of 1 µg/dL in Australia.

When should a mother stop breastfeeding because of lead?

The answer is probably NEVER, unless she has severe lead poisoning. This could result from recent exposure to lead, for example, from:

• renovating a lead-contaminated house (paint/ceiling dust),
• diet with high lead (including beverages),
• traditional medicines containing lead, cosmetics containing lead (see Table 1),
• poorly manufactured pottery and/or crystal glassware, or
• from self or a partner working in a lead occupation, etc.

In all of the above cases, the most important step is to remove the mother from the source of lead, or remove the source from the mother; and to monitor the mother’s lead levels.

 Or: If she has been exposed to lead over a long period of time, such as in a smelter environment (e.g. Mexico, see Table 1), then there is opportunity for build-up of lead in bones. This lead can be released during pregnancy and breastfeeding, with a larger amount released during lactation (Gulson et al., 1998).

In some lead-rich environments, however, such as the Broken Hill mining community, the mothers have blood leads <10 µg/dL (Gulson et al., 1994).

If a pregnant woman is concerned that she may have suffered a high exposure from lead, either as an acute dose (short-term such as from renovating a lead-contaminated house), or from chronic exposure (long-term), it would be worthwhile to have her blood lead tested in the 3 trimesters when she is having other normal pregnancy tests performed and then speak to a specialist.

If the blood lead levels are <10 µg/dL then there should be no cause for concern as the amount of lead in breast milk should be only about 5% - or probably less - of that in her blood (Gulson et al., submitted). As an example, Baum and Shannon (1996) describe two subjects in the USA whose blood leads were 34 and 29 µg/dL. The breast milk contained <10 ppb (see Table 1). If a mother’s blood lead level is above 20 µg/dL, it is recommended that a test of the breast milk should be undertaken.

Even if wholly breast feeding, at these low levels, the impact on blood lead of the infant will be small (estimations based on the Physiologically based Pharmacokinetic Model of Ellen O'Flaherty of the University of Cincinnati Medical Centre 1995).

If a mother’s breast milk lead levels are in the hundreds of parts per billion range, it may be worth considering not breast feeding, in consultation with expert medical opinion.

What can be done to reduce lead moving from bones into breast milk?

It is well established that there is an inverse relationship between calcium intake and uptake of lead. Furthermore, the preliminary data obtained by us (Gulson et al., 1998) indicate that intake of calcium supplements can reduce the amount of lead mobilised from the mother's skeleton during pregnancy.

The U.S. National Institute of Health Consensus Conference on Optimal Calcium Intake (1994) recommended that for pregnant and lactating women the optimal daily intake of calcium should be 1200 mg/day.

References

1. Astrup-Jensen A, Slorach SA (Editors). Chemical contaminants in human breast milk. CRC Press Baton Rouge USA (1991).

2. Baum CR, Shannon MW. Lead in breast milk. Pediatrics 97: 932 (1996).

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5. Gulson BL, Mizon KJ, Law AJ, Korsch MJ, Davis JJ. Source and Pathways of Lead in Humans from Broken Hill Mining Community - an Alternative Use of Exploration Methods. Economic Geology, 89: 889-908 (1994).

6. Gulson BL, Jameson CW, Mahaffey KR, Mizon KJ, Korsch MJ, Vimpani G. Pregnancy increases mobilization of lead from maternal skeleton. J Lab Clin Med 130: 51-62(1997).

7. Gulson BL, Mahaffey KR, Jameson CW, Mizon KJ, Korsch MJ, Cameron MA, Eisman JA. Mobilization of lead from the skeleton during the post-natal period is larger than during pregnancy. J Lab Clin Med in press (1998).

8. Gulson BL, Jameson CW, Mahaffey KR, Mizon KJ, Patison N, Law AJ, Korsch MJ, Relationships of Lead in Breast Milk to Lead in Blood, Urine and Diet of the Infant and Mother. Submitted to Environ Health Perspectives.

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