Season modifies the relationship between bone and blood lead levels: the Normative Aging Study

Association of environmental tobacco smoke (ETS) with lead and cadmium concentrations in biological samples of children and women: systematic review and meta-analysis

OBJECTIVES

Previous literature has shown that heavy metals (HMs) in cigarette smoke have been overestimated, and second-hand smoke (SHS) has recently raised public concern. This study aimed to review the effects of passive tobacco exposure on lead (Pb) and cadmium (Cd) concentrations of children and women in different biological samples.

CONTENT

In this systematic review, two independent researchers assessed different databases/search engines including PubMed, Web of Science, Scopus, and Google Scholar using Mesh terms and Text Words. Studies between January 2000 and May 2022 were included. After quality assessment, studies with sufficient data were included in the meta-analysis. A fixed or random model was used to pool the results in a meta-analysis. Heterogeneity between the studies was assessed by using I-square and Q tests. Forest plots demonstrating the point and pooled estimates were provided.

SUMMARY

A total of 976 studies were obtained from different databases and finally 17 studies meet our criteria and were included in our systematic review. Out of 17 studies, six studies had sufficient data for analysis and were included in the meta-analysis. The results of the meta-analysis showed a significant difference in blood lead concentrations (BLC) between the children with SHS exposure and the control group (Hedges' g: 2.44, 95% CI: 1.01-3.86, p<0.05). Also, there were significant differences in hair levels of Cd (Hedges' g: 0.66, 95% CI: 0.04, 1.28, p<0.05) and Pb (Hedges' g: 0.94, 95% CI: 0.05, 1.83, p<0.05) between children with SHS exposure compared to the control group.

OUTLOOK

The results of the present meta-analysis showed that passive smokers had higher Pb and Cd concentrations than those who were not exposed to cigarette smoke.

Blood pressure and renal function responses in workers exposed to lead for up to six years

The Study for Promotion of Health in Recycling Lead (SPHERL) assessed the blood pressure (BP) and renal function (RF) responses for up to 6 years in the workers without previous occupational lead exposure. BP was the average of five consecutive readings and the estimated glomerular filtration rate was derived from serum creatinine (eGFRcrt) and cystatin C (eGFRcys). Blood lead (BL) was measured by inductively coupled plasma mass spectrometry (detection limit 0.5 μg/dL). The statistical methods included multivariable-adjusted mixed models and interval-censored Cox regression analysis. The 234 workers analyzed were on average 28.5 years old and included 91.9% men. The baseline BL concentration was 4.35 μg/dL and increased 3.17-fold over follow-up (median: 2.03 years; range: 0.92-6.45 years). The changes in BP and RF were not significantly correlated with the follow-up-to-baseline BL ratio (p ≥ .51 and p ≥ .18, respectively). The fully-adjusted changes in systolic/diastolic BP associated with a doubling of BL were -0.25/-0.12 mm Hg (CI: -0.94 to 0.44/-0.66 to 0.42 mm Hg). Accordingly, the incidence of stage-1 or -2 hypertension was not associated with the BL change (p ≥ .063). Similarly, the changes in eGFRcrt and eGFRcys associated with a 3-fold BL increment were not significant, amounting to -0.70 mL/min/1.73 m2 (CI: -1.70 to 0.30 mL/min/1.73 m2 ) and -1.06 mL/min/1.73 m2 (-2.16 to 0.03 mL/min/1.73 m2 ). In conclusion, the BP and RF responses to an over 3-fold BL increment were small and not significant confirming the safety of modern lead-handing facilities operating under current safety rules.

Public and occupational health risks related to lead exposure updated according to present-day blood lead levels

Lead is an environmental hazard that should be addressed worldwide. Over time, human lead exposure in the western world has decreased drastically to levels comparable to those among humans living in the preindustrial era, who were mainly exposed to natural sources of lead. To re-evaluate the potential health risks associated with present-day lead exposure, a two-pronged approach was applied. First, recently published population metrics describing the adverse health effects associated with lead exposure at the population level were critically assessed. Next, the key results of the Study for Promotion of Health in Recycling Lead (SPHERL; NCT02243904) were summarized and put in perspective with those of the published population metrics. To our knowledge, SPHERL is the first prospective study that accounted for interindividual variability between people with respect to their vulnerability to the toxic effects of lead exposure by assessing the participants' health status before and after occupational lead exposure. The overall conclusion of this comprehensive review is that mainstream ideas about the public and occupational health risks related to lead exposure urgently need to be updated because a large portion of the available literature became obsolete given the sharp decrease in exposure levels over the past 40 years.

Early childhood lead exposure and adolescent heart rate variability: A longitudinal cohort study

Lead is a known neurotoxicant with many detrimental health effects, including neurocognitive deficits and cardiovascular and metabolic disorders. However, few studies have tested the association between lead exposure and the physiological stress response, which in and of itself may act as a precursor to and/or underlying mechanism of detrimental health outcomes. The purpose of this study was to examine the influence of early childhood and early adolescent low-level lead exposure on early adolescent heart rate variability, a widely-used measure of physiological stress. Participants were 408 children from Jintan, China for whom blood lead levels were measured between 3 and 5 years (early childhood) and again at 12 years (early adolescence). Heart rate variability was assessed at 12 years while participants underwent an induced stress task utilizing the ratio of low to high frequency (LF/HF) ECG measures. Mean blood lead levels in the cohort were 6.63 mcg/dl and 3.10 mcg/dl at 3-5 years and 12 years, respectively. Blood lead levels at 3-5 years of age (β 0.06, p = 0.027), but not at age 12 (β -0.05, p = 0.465), were significantly associated with LF/HF measures while controlling for multiple sociodemographic variables, potentially reflecting a dysregulated stress response with a shift towards sympathetic dominance. These findings suggest that early childhood lead exposure may have a detrimental influence on early adolescent autonomic responses to acute stress, which holds implications for cardiovascular health and overall growth and development.

Two-year responses of renal function to first occupational lead exposure

Introduction

Whether in advanced countries lead exposure still contributes to renal impairment is debated, because blood lead (BL) level is declining toward preindustrial levels and because longitudinal studies correlating renal function and BL changes over time are scarce.

Methods

The Study for Promotion of Health in Recycling Lead (SPHERL) evaluated the 2-year renal function responses in 251 workers (mean age, 29.7 years) transiting from environmental to occupational exposure. Main study end point was the estimated glomerular filtration rate (eGFR) derived from serum creatinine (eGFRcrt), cystatin C (eGFRcys), or both (eGFRcc). BL level was measured by inductively coupled plasma mass spectrometry (detection limit 0.5 μg/dl).

Results

In the follow-up, mean baseline BL level of 4.13 μg/dl increased 3.30-fold. In fully adjusted mixed models, additionally accounting for the within-participant clustering of the 1- and 2-year follow-up data, a 3-fold BL level increment was not significantly correlated with changes in eGFR with estimates amounting to −0.86 (95% CI: −2.39 to 0.67), −1.58 (−3.34 to 0.18), and −1.32 (−2.66 to 0.03) ml/min per 1.73 m² for eGFRcrt, eGFRcys, or eGFRcc, respectively. Baseline BL level and the cumulative lead burden did not materially modify these estimates, but baseline eGFR was a major determinant of eGFR changes showing regression to the mean during follow-up. Responses of serum osmolarity, urinary gravity, or the urinary albumin-to-creatinine ratio (ACR) were also unrelated to the BL level increment. The age-related decreases in eGFRcrt, eGFRcys, and eGFRcc were −1.41, −0.96, and −1.10 ml/min per 1.73 m², respectively.

Conclusion

In the current study, the 2-year changes in renal function were unrelated to the increase in BL level. However, given the CIs around the point estimates of the changes in eGFRcc and eGFRcys, a larger study with longer follow-up is being planned.

Two-year neurocognitive responses to first occupational lead exposure

Objectives Lead exposure causes neurocognitive dysfunction in children, but its association with neurocognition in adults at current occupational exposure levels is uncertain mainly due to the lack of longitudinal studies. In the Study for Promotion of Health in Recycling Lead (NCT02243904), we assessed the two-year responses of neurocognitive function among workers without previous known occupational exposure newly hired at lead recycling plants. Methods Workers completed the digit-symbol test (DST) and Stroop test (ST) at baseline and annual follow-up visits. Blood lead (BL) was measured by inductively coupled plasma mass spectrometry (detection limit 0.5 µg/dL). Statistical methods included multivariable-adjusted mixed models with participants modelled as random effect. Results DST was administered to 260 participants (11.9% women; 46.9%/45.0% whites/Hispanics; mean age 29.4 years) and ST to 168 participants. Geometric means were 3.97 and 4.13 µg/dL for baseline BL, and 3.30 and 3.44 for the last-follow-up-to-baseline BL ratio in DST and ST cohorts, respectively. In partially adjusted models, a doubling of the BL ratio was associated with a 0.66% [95% confidence interval (CI) 0.03-1.30; P=0.040] increase in latency time (DST) and a 0.35% (95% CI ‑1.63-1.63; P=0.59) decrease in the inference effect (ST). In fully adjusted models, none of the associations of the changes in the DST and ST test results with the blood lead changes reached statistical significance (P≥0.12). Conclusions An over 3-fold increase in blood lead over two years of occupational exposure was not associated with a relevant decline in cognitive performance.

Two-Year Responses of Heart Rate and Heart Rate Variability to First Occupational Lead Exposure

[Figure: see text].

Two-Year Responses of Office and Ambulatory Blood Pressure to First Occupational Lead Exposure

Supplemental Digital Content is available in the text.

Lead exposure causing hypertension is the mechanism commonly assumed to set off premature death and cardiovascular complications. However, at current exposure levels in the developed world, the link between hypertension and lead remains unproven. In the Study for Promotion of Health in Recycling Lead (URL: https://www.clinicaltrials.gov; Unique identifier: NCT02243904), we recorded the 2-year responses of office blood pressure (average of 5 consecutive readings) and 24-hour ambulatory blood pressure to first occupational lead exposure in workers newly employed at lead recycling plants. Blood lead (BL) was measured by inductively coupled plasma mass spectrometry (detection limit 0.5 µg/dL). Hypertension was defined according to the 2017 American College of Cardiology/American Heart Association guideline. Statistical methods included multivariable-adjusted mixed models with participants modeled as a random effect and interval-censored Cox regression. Office blood pressure was measured in 267 participants (11.6% women, mean age at enrollment, 28.6 years) and ambulatory blood pressure in 137 at 2 follow-up visits. Geometric means were 4.09 µg/dL for baseline BL and 3.30 for the last-follow-up-to-baseline BL ratio. Fully adjusted changes in systolic/diastolic blood pressure associated with a doubling of the BL ratio were 0.36/0.28 mm Hg (95% CI, −0.55 to 1.27/−0.48 to 1.04 mm Hg) for office blood pressure and −0.18/0.11 mm Hg (−2.09 to 1.74/−1.05 to 1.27 mm Hg) for 24-hour ambulatory blood pressure. The adjusted hazard ratios of moving up across hypertension categories for a doubling in BL were 1.13 (0.93–1.38) and 0.84 (0.57–1.22) for office blood pressure and ambulatory blood pressure, respectively. In conclusion, the 2-year blood pressure responses and incident hypertension were not associated with the BL increase on first occupational exposure.

Interpretation of Population Health Metrics: Environmental Lead Exposure as Exemplary Case

Our objective was to gain insight in the calculation and interpretation of population health metrics that inform disease prevention. Using as model environmental exposure to lead (ELE), a global pollutant, we assessed population health metrics derived from the Third National Health and Nutrition Examination Survey (1988 to 1994), the GBD (Global Burden of Disease Study 2010), and the Organization for Economic Co-operation and Development. In the National Health and Nutrition Examination Survey, the hazard ratio relating mortality over 19.3 years of follow-up to a blood lead increase at baseline from 1.0 to 6.7 µg/dL (10th–90th percentile interval) was 1.37 (95% CI, 1.17–1.60). The population-attributable fraction of blood lead was 18.0% (10.9%–26.1%). The number of preventable ELE-related deaths in the United States would be 412 000 per year (250 000–598 000). In GBD 2010, deaths and disability-adjusted life-years globally lost due to ELE were 0.67 million (0.58–0.78 million) and 0.56% (0.47%–0.66%), respectively. According to the 2017 Organization for Economic Co-operation and Development statistics, ELE-related welfare costs were $1 676 224 million worldwide. Extrapolations from the foregoing metrics assumed causality and reversibility of the association between mortality and blood lead, which at present-day ELE levels in developed nations is not established. Other issues limiting the interpretation of ELE-related population health metrics are the inflation of relative risk based on outdated blood lead levels, not differentiating relative from absolute risk, clustering of risk factors and exposures within individuals, residual confounding, and disregarding noncardiovascular disease and immigration in national ELE-associated welfare estimates. In conclusion, this review highlights the importance of critical thinking in translating population health metrics into cost-effective preventive strategies.

Blood Lead Concentrations of Children in the United States: A Comparison of States Using Two Very Large Databases

OBJECTIVES

To determine whether there are substantial differences by state between 2 large datasets in the proportion of children with elevated blood lead levels (BLLs); to identify states in which the percentage of elevated BLLs is high in either or both datasets; and to compare the percentage of elevated BLLs in individual states with those of children living in Flint, Michigan, during the months when these children were exposed to lead-contaminated drinking water.

STUDY DESIGN

Tables of BLLs for individual states from the Quest Diagnostics and the Centers for Disease Control and Prevention datasets for 2014-2015, containing more than 3 million BLLs of young children?<?6 years old, were constructed to compare the Quest Diagnostics and Centers for Disease Control and Prevention data with one another and with BLLs available for Flint children for 2014-2015.

RESULTS

For some states, the percentages of BLLs ?5.0?µg/dL are similar in the 2 datasets, whereas for other states, the datasets differ substantially in the percentage of BLLs ?5.0?µg/dL. The percentage of BLLs ?5.0?µg/dL is greater in some states in both datasets than observed in Flint when children were exposed to contaminated water.

CONCLUSION

The data presented in this study can be a resource for pediatricians and public health professionals involved in the design of state programs to reduce lead exposure (primary prevention) and identify children with elevated BLLs (secondary prevention).

Vincent van Gogh (1853-90): the plumbic artist

Following Vincent van Gogh's death in 1890, numerous physicians have offered diagnostic opinions regarding his still unverified illness. The discovery that he had ingested leaded oil paints prompted research that revealed his exposure to additional sources of lead and other toxic substances for 13 years before death. His complaints, derived from poignant letters to his brother, added compelling evidence that he had suffered neurotoxicity, encephalopathy and other consequences of lead. Vincent's suicide may have been precipitated by plumbism. Mankind has endured lead's presence for millennia, yet its destructive effects have been recognized sporadically. That symptoms of plumbism mimic other illnesses should prod a heightened index of suspicion. Had it not been for the financial and emotional support of Vincent by his brother, Theo, and the dedication of the latter's wife, Johanna, the artist's genius might never have been recognized. Widowed by the death of her husband six months after Vincent's demise, Johanna(1) remained the guardian of the painter's extraordinary artistic and literary output until critical acclaim established him as one of Europe's greatest artists. Her efforts, assisted by her son, in framing and exhibiting van Gogh's works, were crucial. She then translated and systematized his more than 750 letters to Theo, their sister, Willemien, their mother, fellow artists and others.(2).

Elevated blood lead concentrations and vitamin D deficiency in winter and summer in young urban children

BACKGROUND

It is widely recognized that blood lead concentrations are higher in the summer than in winter. Although the effects of some environmental factors such as lead in dust on this phenomenon have been studied, relationships to sunlight-induced vitamin D synthesis have not been adequately investigated. Vitamin D status is influenced by the diet, sunlight exposure, age, skin pigmentation, and other factors, and may modify gastrointestinal lead absorption or release of lead stored in bones into the bloodstream.

OBJECTIVE AND METHODS

We collected paired blood samples from 142 young, urban African-American and Hispanic children in the winter and summer to study the seasonal increase in blood lead and its relationships to vitamin D nutrition, age, and race.

RESULTS

A winter/summer (W/S) increase in blood lead concentrations of 32.4% was found for children 1-3 years of age. There was a smaller W/S increase of 13.0% in children 4-8 years of age. None of the 51 Hispanic children had an elevated blood lead concentration (> or = 10 microg/dL) during the winter, and only one had an elevated summertime concentration. In contrast, elevated blood lead concentrations were frequent in the 91 African-American children, especially those 1-3 years of age. For the latter, the percentage with elevated blood lead levels increased from 12.2% in winter to 22.5% in summer. A 1.2% W/S increase in serum 25-hydroxy-vitamin D (serum 25-OH-D) concentrations was found for children 1-3 years of age. However, in children 4-8 years of age the W/S increase in serum 25-OH-D was much larger-33.6%. The percentages of children with low (< 16 microg/L) serum 25-OH-D concentrations were 12.0% in winter and 0.7% in summer and were consistently greater in African-American than in Hispanic children. The seasonal increases in blood lead and serum 25-OH-D in children 4-8 years of age were significantly associated.

CONCLUSION

The higher summertime serum 25-OH-D concentrations for the 4- to 8-year-old children are likely caused by increased sunlight-induced vitamin D synthesis and may contribute to the seasonal increase in blood lead. Age and race are key factors that affect blood lead and vitamin D nutrition, as well as their interactions, in young urban children.

Mercury and lead during breast-feeding

Hg and Pb are of public health concern due to their toxic effects on vulnerable fetuses, persistence in pregnant and breast-feeding mothers, and widespread occurrence in the environment. To diminish maternal and infant exposure to Hg and Pb, it is necessary to establish guidelines based on an understanding of the environmental occurrence of these metals and the manner in which they reach the developing human organism. In the present review, environmental exposure, acquisition and storage of these metals via maternal–infant interaction are systematically presented. Though Hg and Pb are dispersed throughout the environment, the risk of exposure to infants is primarily influenced by maternal dietary habits, metal speciation and interaction with nutritional status. Hg and Pb possess similar adverse effects on the central nervous system, but they have environmental and metabolic differences that modulate their toxicity and neurobehavioural outcome in infant exposure during fetal development. Hg is mainly found in protein matrices of animal flesh (especially fish and shellfish), whereas Pb is mainly found in osseous structures. The potential of maternal acquisition is higher and lasts longer for Pb than for Hg. Pb stored in bone has a longer half-life than monomethyl-mercury acquired from fish. Both metals appear in breast milk as a fraction of the levels found in maternal blood supplied to the fetus during gestation. Habitual diets consumed by lactating mothers pose no health hazard to breast-fed infants. Instead, cows' milk-based formulas pose a greater risk of infant exposure to neurotoxic substances.

Comparison of lead residues among avian bones

To determine if significant differences exist in lead (Pb) accumulation in different bones, especially those most often used for bone-Pb studies in wildlife, we compared Pb concentrations in radius, ulna, humerus, femur, and tibia of Common Eider (Somateria mollissima); and radius/ulna (combined), femur, and tibia of American Woodcock (Scolopax minor). There were no significant differences in bone-Pb concentrations among woodcock bones over a wide range of Pb concentrations (3-311 microg/g). In eider, where bone-Pb concentrations were low (<10 microg/g), leg bones had significantly higher Pb concentrations (approximately 30-40%) than wing bones from the same individuals. The variation among individual birds was greater than the variation among different bones within a bird. Based on our findings, we conclude that one type of bone may be substituted for another in bone-Pb studies although the same bone type should be analyzed for all birds within a study, whenever possible.

Active and passive smoking and blood lead levels in U.S. adults: data from the Third National Health and Nutrition Examination Survey

Lead is a component of tobacco and tobacco smoke. We examined the relationship between current, former, and passive smoking and blood lead levels in a nationally representative sample of 16,458 U.S. adults, aged 17 years or older, who participated in the Third National Health and Nutrition Examination Survey (1988-1994). We used linear and logistic regression modeling, adjusting for known covariates, to determine the relationship between smoking and blood lead levels. Geometric mean blood lead levels were 1.8 microg/dl, 2.1 microg/dl, and 2.3 microg/dl in never-smokers with no, low, and high cotinine levels, respectively. Levels were 2.9 microg/dl in former smokers and 3.5 microg/dl in current smokers. The adjusted linear regression model showed that geometric mean blood lead levels were 30% higher (95% CI = 24%-36%) in adults with high cotinine levels than they were in those with no detectable cotinine. Active and passive smoking is associated with increased blood lead levels in U.S. adults.

Vitamin D is associated with improved survival in early-stage non-small cell lung cancer patients

Vitamin D may inhibit the development and progression of a wide spectrum of cancers. We investigated the associations of surgery season and vitamin D intake with recurrence-free survival (RFS) and overall survival in 456 early-stage non-small cell lung cancer patients. The data were analyzed using log-rank test and Cox proportional hazards models. The median (range) follow-up time was 71 (0.1-140) months, with 161 recurrence and 231 deaths. Patients who had surgery in summer had a better RFS than those who had surgery in winter (adjusted hazard ratio, 0.75; 95% confidence interval, 0.56-1.01), with 5-year RFS rates of 53% (45-61%) and 40% (32-49%), respectively (P = 0.10, log-rank test). Similar association between surgery season and RFS was found among the 321 patients with dietary information (P = 0.33, log-rank test). There was no statistically significant association between vitamin D intake and RFS. Because both season and vitamin D intake are important predictors for vitamin D levels, we investigated the joint effects of surgery season and vitamin D intake. Patients who had surgery during summer with the highest vitamin D intake had better RFS (adjusted hazard ratio, 0.33; 95% confidence interval, 0.15-0.74) than patients who had surgery during winter with the lowest vitamin D intake, with the 5-year RFS rates of 56% (34-78%) and 23% (4-42%), respectively. Similar associations of surgery season and vitamin D intake with overall survival were also observed. In conclusion, the joint effects of surgery season and recent vitamin D intake seem to be associated with the survival of early-stage non-small cell lung cancer patients.

A noninvasive isotopic approach to estimate the bone lead contribution to blood in children: implications for assessing the efficacy of lead abatement

Lead hazard control measures to reduce children's exposure to household lead sources often result in only limited reductions in blood lead levels. This may be due to incomplete remediation of lead sources and/or to the remobilization of lead stores from bone, which may act as an endogenous lead source that buffers reductions in blood lead levels. Here we present a noninvasive isotopic approach to estimate the magnitude of the bone lead contribution to blood in children following household lead remediation. In this approach, lead isotopic ratios of a child's blood and 5-day fecal samples are determined before and after a household intervention aimed at reducing the child's lead intake. The bone lead contribution to blood is estimated from a system of mass balance equations of lead concentrations and isotopic compositions in blood at the different times of sample collection. The utility of this method is illustrated with three cases of children with blood lead levels in the range of 18-29 microg/dL. In all three cases, the release of lead from bone supported a substantial fraction of the measured blood lead level postintervention, up to 96% in one case. In general, the lead isotopic compositions of feces matched or were within the range of the lead isotopic compositions of the household dusts with lead loadings exceeding U.S. Environmental Protection Agency action levels. This isotopic agreement underscores the utility of lead isotopic measurements of feces to identify household sources of lead exposure. Results from this limited number of cases support the hypothesis that the release of bone lead into blood may substantially buffer the decrease in blood lead levels expected from the reduction in lead intake.

Blood lead changes during pregnancy and postpartum with calcium supplementation

Pregnancy and lactation are times of physiologic stress during which bone turnover is accelerated. Previous studies have demonstrated that there is increased mobilization of lead from the maternal skeleton at this time and that calcium supplementation may have a protective effect. Ten immigrants to Australia were provided with either calcium carbonate or a complex calcium supplement (approximately 1 g/day) during pregnancy and for 6 months postpartum. Two immigrant subjects who did not conceive acted as controls. Sampling involved monthly venous blood samples throughout pregnancy and every 2 months postpartum, and quarterly environmental samples and 6-day duplicate diets. The geometric mean blood lead at the time of first sampling was 2.4 microg/dL (range, 1.4-6.5). Increases in blood lead during the third trimester, corrected for hematocrit, compared with the minimum value observed, varied from 10 to 50%, with a geometric mean of 25%. The increases generally occurred at 6-8 months gestation, in contrast with that found for a previous cohort, characterized by very low calcium intakes, where the increases occurred at 3-6 months. Large increases in blood lead concentration were found during the postpartum period compared with those during pregnancy; blood lead concentrations increased by between 30 and 95% (geometric mean 65%; n = 8) from the minimum value observed during late pregnancy. From late pregnancy through postpartum, there were significant increases in the lead isotopic ratios from the minimum value observed during late pregnancy for 3 of 8 subjects (p < 0.01). The observed changes are considered to reflect increases in mobilization of lead from the skeleton despite calcium supplementation. The identical isotopic ratios in maternal and cord blood provide further confirmation of placental transfer of lead. The extra flux released from bone during late pregnancy and postpartum varies from 50 to 380 microg lead (geometric mean, 145 microg lead) compared with 330 microg lead in the previous cohort. For subjects replete in calcium, the delay in increase in blood lead and halving of the extra flux released from bone during late pregnancy and postpartum may provide less lead exposure to the developing fetus and newly born infant. Nevertheless, as shown in several other studies on calcium relationships with bone turnover, calcium supplementation appears to provide limited benefit for lead toxicity during lactation.