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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
Pb Milk (ppb) |
no. |
Country |
Date |
Reference |
| 0.7 ± 0.7 |
9 |
Australia |
1998 |
Gulson et al. (submitted) |
| 0.7 ± 0.4 |
75 |
Sweden |
1995 |
Palminger Hallen et al. |
| 1.04
mean / 0.55 median |
210 |
Canada |
1986 |
Dabeka
et al. |
| 1.7 |
72 |
Czech’ia |
1989 |
Zahradnicek et al. |
| 2.6 ± 1.6 |
27 |
Germany |
1988 |
Schramel et al. |
| 2.8 ± 1.6 |
39 |
U.S.A. |
1984 |
Rockway et al. |
| <10 |
2 |
U.S.A. |
1996 |
Baum et al. |
| 13.3
(urban), 9.1 (rural) |
20 20 |
Germany |
1985 |
Sternowsky
& Wesselowski |
| 17 ± 2 |
100 |
U.S.A. |
1985 |
Rabinowitz et al. |
| 21 |
97 |
Scotland |
1982 |
Moore et al. |
| 25 |
35 |
Mexico |
1993 |
Namihara et al. |
25
(urban),
21 (rural) |
89 91 |
Malaysia |
1983 |
Huat
et al. |
| 30 |
39 |
U.K. |
1993 |
Richmond et al. |
| 36 ± 15 |
51 |
Austria |
1993 |
Plockinger et al. |
| 48 ± 12 |
114 |
Malaysia |
1985 |
Ong et al. |
| 70 ± 17 |
25 |
UA Emirates |
1994 |
Sokas et al. |
127
(urban),
46 (rural) |
20 34 |
Italy |
1992 |
Guidi
et al. |
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
-
Astrup-Jensen A, Slorach SA
(Editors). Chemical contaminants in human breast milk. CRC Press Baton Rouge USA (1991).
-
Baum CR, Shannon MW. Lead in breast
milk. Pediatrics 97: 932 (1996).
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Dabeka RW, Karpinski KF, McKenzie
AD, Bajdik CD. Survey of lead, cadmium and fluoride in human milk and correlation of
levels with environmental and food factors. Fd Chem Toxic 24: 913-921 (1986).
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Guidi B, Ronchi S, Ori E, Varni PF,
Cassindri TT, Tripodi A, Borghi A, Mattei F, Demaria F, Galavotti E, et al. Concentrazione
del piombo nel latte materno di donne residenti in aree urbane rispetto a donne residenti
in aree rurali. Pediaitr Med Chir 14 611-616 (1992).
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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).
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Gulson BL, Jameson CW, Mahaffey KR,
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skeleton. J Lab Clin Med 130: 51-62(1997).
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Huat LH, Zakariya D, Hoon K. Lead
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Occup Environ Health 53: 181-187 (1984).
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blood, and the blood of the newborn. Biol Trace Element Res 16: 67-75 (1988).
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