Cumulative concentrations of blood lead and postural stability

Relationship between Postural Stability, Lead Content, and Selected Parameters of Oxidative Stress

This study attempts to determine whether the increased blood lead concentration affects the posturographic test and to determine the relationship between the parameters of posture stability and selected parameters of oxidative stress. The study population consisted of 268 male employees and was divided into two equal subgroups, depending on the lead content in the blood. A posturographic examination was performed. Concentrations of lead, cadmium, zinc protoporphyrin, selected essential elements, and selected markers of oxidative stress in the blood were tested. Higher blood lead concentrations positively affected the values of the sway results: the field and the mean velocity of the center of the feet pressure in posturography. The absolute value of the proprioception ratio was similar in both subgroups. The content of malondialdehyde shows a statistically significantly higher value in a subgroup with high blood lead concentration and exhibits significant correlations only with some of the posturography parameters. The lipofuscin content in erythrocytes correlates with the results of the posturography test. Zinc protoporphyrin, total oxidant status, total antioxidant capacity, selected minerals, and metals did not correlate with the results of the posturography test. In conclusion, posturographic results correlate only with selected markers of oxidative stress, so it can be assumed that the effect on the body balance is only partial.

Lead and cadmium levels and balance and vestibular dysfunction among adult participants in the National Health and Nutrition Examination Survey (NHANES) 1999-2004

BACKGROUND

Few studies have been conducted to identify risk factors for balance and vestibular dysfunction in general populations, but previous studies have reported evidence of adverse effects of lead and cadmium on balance control in high-risk groups.

OBJECTIVE

We evaluated the relationship between blood lead and cadmium levels and balance and vestibular dysfunction in a general population study.

METHODS

We analyzed data from the 1999-2004 National Health and Nutrition Examination Survey (NHANES) of 5,574 adults ≥ 40 years of age. Balance dysfunction was evaluated by the Romberg Test of Standing Balance on Firm and Compliant Support Surfaces, which examines the ability to stand unassisted using four test conditions to evaluate vestibular system, vision, and proprioception inputs that contribute to balance. Blood levels of lead and cadmium were measured by atomic absorption spectrometry. Associations were estimated using logistic regression models adjusted for potential confounders. Associations with time to loss of balance were estimated using adjusted Cox proportional hazard models.

RESULTS

The adjusted odds ratio (OR) for balance dysfunction in association with the highest quintile (3.3-48 µg/dL) versus the lowest quintile (< 1.2 µg/dL) of lead was 1.42 [95% confidence interval (CI): 1.07, 1.89]. The corresponding OR for cadmium (0.9-7.4 µg/L vs. < 0.2 µg/L) was 1.27 (95% CI: 1.01, 1.60). The adjusted hazard ratio for time to failure for the most physiologically challenging balance test among subjects with the highest vs. lowest quintiles of blood lead was 1.24 (95% CI: 1.04, 1.48). Cadmium levels were not associated with time to failure.

CONCLUSIONS

Our findings suggest that blood lead and cadmium levels may be associated with balance and vestibular dysfunction in a general sample of U.S. adults.

Motor alterations induced by chronic lead exposure

Lead (Pb) as other environmental neurotoxicants substances has the capability to interfere with many biochemical events present in cells throughout the body and it can produce a wide spectrum of alterations in many organs and systems. Among that alterations induced by Pb exposure in adults and children those involving motor system dysfunction represent a common public health problem. The review summarizes the sources of lead exposures in both occupational and residential environments and motor deficits induced by chronic Pb exposure taking in account the last literature in the field. We wish to focus on the current state of knowledge concerning the long-lasting neurological effects of Pb in motor functions and to correlate the neurological deficits induced by Pb exposure in animal models with those reported in humans. The great interest in whether exposure to Pb can cause long-term, progressive declines in central nervous system (CNS) function have revealed that Pb exposure is involved in chronic CNS diseases such Parkinson's and poor motor coordination in children.

Relationship of blood lead levels to incident nonspine fractures and falls in older women: the study of osteoporotic fractures

Lead is stored in the skeleton and can serve as an endogenous source for many years. Lead may influence the risk of fracture, through direct effects on bone strength or indirectly by disturbing neuromuscular function and increasing the risk of falls. The objective of this analysis is to test the hypothesis that women with higher blood lead levels experience higher rates of falls and fracture. This was a prospective cohort study of 533 women 65-87 yr of age enrolled in the Study of Osteoporotic Fractures at two U.S. research centers (Baltimore, MD; Monongahela Valley, PA) from 1986 to 1988. Blood lead levels (in microg/dl) were measured in 1990-1991 by atomic absorption spectrophotometry and classified as "low" (<or=3; lower 15th percentile, referent); "medium" (4-7); or "high" (>or=8; upper 15th percentile). Total hip BMD was measured by DXA twice, 3.55 yr apart. Information on falls was collected every 4 mo for 4 yr. Incident nonspine fractures were identified and confirmed over 10 yr. Cox proportional hazards models were used to estimate the hazard ratio (HR) and 95% CI of fracture. Generalized estimating equations were used to calculate the incident rate ratio of falls (95% CI). The mean blood lead level was 5.3 +/- 2.3 (SD) microg/dl (range, 1-21 microg/dl). Baseline BMD was 7% lower in total hip and 5% lower in femoral neck in the highest compared with lowest blood lead group (p < 0.02). Hip bone loss tended to be greater in the high lead group, but differences were not significant. In multivariable adjusted models, women with high blood lead levels had an increased risk of nonspine fracture (HR = 2.50; 95% CI = 1.25, 5.03; p trend = 0.016) and higher risk of falls (incident rate ratio = 1.62; 95% CI = 1.07, 2.45; p trend = 0.014) compared with women with lowest lead level. Blood lead levels are associated with an increased risk of falls and fractures, extending the negative health consequences of lead to include osteoporotic fractures.

Critical dose of lead affecting postural balance in workers

BACKGROUND

The threshold blood lead (BPb) level for nervous system dysfunction in adults has been estimated to be 30-40 microg/dl. This study was carried out to estimate the critical dose of lead affecting the neuromotor function in workers by introducing the benchmark dose (BMD) approach, as well as to identify the specific postural sway to lead exposure.

METHODS

Postural sway parameters with spectral analysis were compared between 121 lead workers with BPb levels of 6-89 (mean 40) microg/dl and 60 unexposed controls.

RESULTS

All sway parameters, except for sagittal sways with eyes open, were significantly larger in the lead workers than in the controls; also, the Romberg quotient for sagittal sway was significantly higher in the lead workers. The BPb level in the lead workers was significantly related to sagittal sways at 1-2 Hz and 2-4 Hz with eyes open, and sagittal and transversal sways at 1-2 Hz and 2-4 Hz with eyes closed. The BMD levels of BPb (i.e., lower 95% confidence limits of BMD) were estimated to be 12.1-17.3 (mean 14.4) microg/dl for postural sway.

CONCLUSIONS

Neuromotor dysfunction in lead workers may be initiated at BPbs below the level previously accepted as effectless, and be characterized mainly by an increased sway of high frequency (1-4 Hz) in the sagittal direction with eyes closed (high Romberg quotient).

Estimating the global burden of disease of mild mental retardation and cardiovascular diseases from environmental lead exposure

The disease burden from exposure to lead resulting in mild mental retardation (due to IQ point decreases) and cardiovascular outcomes (due to increases in blood pressure) was estimated at a global level. Blood lead levels were compiled from the literature for 14 geographical regions defined by the World Health Organization according to location and adult and child mortality rates. Adjustments were applied to these levels, where appropriate, to account for recent changes relating to the implementation of lead-reduction programs and the lower levels seen in rural populations. It is estimated that mild mental retardation and cardiovascular outcomes resulting from exposure to lead amount to almost 1% of the global burden of disease, with the highest burden in developing regions. This estimate can be used to assess the magnitude of the benefits that could be accrued by increasing the global coverage of lead-reduction programs.

Effect of exposure to lead on postural control in workers

OBJECTIVES

To examine the effect of lead on postural control of workers who have been exposed to lead.

METHODS

63 Male, lead battery workers mean (SD) age 41.0 (7.4) were compared with 48 age matched male controls after excluding those with acute or chronic diseases. Exposed workers had mean (SD) past blood lead concentrations of 37.5 (9.2) micrograms/dl and 11.2 (5.7) years of employment. Postural control was measured with a computerised postural sway measurement system which measured both sway and total movements.

RESULTS

Workers standing straight with eyes open on the bare plates had sway and total movements which were not notably different from controls. On the other hand increased movements were needed in the exposed workers to maintain stability (the general stability quotient 18.2 (5.4) v 15.4 (4.4) in controls, p < 0.01) when standing directly on the foot-plates with closed eyes,, and with the head tilted (15.0 (3.8) v 11.5 (3.0) in controls, p < 0.001). Exposed workers also had a trend for less ability to synchronize anterior posterior and lateral sway in the stress positions (0.0625) than had non-exposed workers. Significant but low correlations were found between the estimate of the chronic internal dose of lead and three of 10 of the postural control measurements, and present lead blood concentrations and only one of the 10 measurements and (r values ranged from 0.21 to 0.31, p < or = 0.03).

CONCLUSIONS

These findings suggest that lead affects postural control in asymptomatic workers. Further studies are warranted to find whether workers with decreased postural control are at increased risk of accidents and the relation, if any, of these measurements with subsequent morbidity.

Bone lead as a biological marker in epidemiologic studies of chronic toxicity: conceptual paradigms

The skeleton contains the majority of the body's lead burden in both children and adults. The half-life of lead in bone is in the range of years to decades, depending on bone type, metabolic state, and subject age, among other things. Measurement of skeletal lead has benefited greatly from the recent development of X-ray fluorescence (XRF) instruments that can make rapid, safe, accurate, and relatively precise measurements of lead in bone. Two types of XRF technologies exist, LXRF and KXRF; this paper focuses on KXRF, which has been the most widely validated and used. KXRF is proving to be a powerful analytical methodology for evaluating bone lead levels as a measure of time-integrated (i.e., cumulative) lead dose in epidemiologic studies of the effects of chronic lead exposure. However, insufficient attention has been given to conceptualizing the paradigms by which bone lead levels reflect lead exposure and by which the skeleton serves as an endogenous source of lead. Consideration of these paradigms, which rely on bone lead kinetics, is necessary for the proper development of a priori hypotheses involving bone lead accumulation and release, the selection of bone sites for measurement by KXRF, and the design of epidemiologic studies involving bone lead dynamics. We discuss and present supporting evidence for a conceptual model that distinguishes two major paradigms of skeletal lead, including 1) bone lead as an indicator of cumulative lead exposure (bone lead as repository), and 2) bone lead as a source of body lead burden that is mobilizable into the circulation (bone lead as source). These two roles are not mutually exclusive. Instead, they are components of the processes controlling lead accumulation into and release from bone over time. Developing successful strategies for distinguishing these two processes in epidemiologic studies will require separate measurements of lead in cortical and trabecular bone and additional measurement of specific markers of bone mineral turnover and resorption. It may also involve developing accurate methods for evaluating lead in labile compartments of the circulation, such as plasma, as a potentially useful and responsive measure of bone lead release, of the partitioning of circulatory lead, and of the toxicological significance of lead released from bone to other target organs.

Postural sway frequency analysis in workers exposed to n-hexane, xylene, and toluene: assessment of subclinical cerebellar dysfunction

To clarify the effects of organic solvents on the postural balance system, 29 male sandal, shoe, and leather factory workers exposed to n-hexane, xylene, and toluene (solvent workers) were examined by computerized static posturography with sway frequency analysis. Concentrations of metabolites of solvents in urine samples taken from the workers in the morning before work ranged from 0.41 to 3.06 (mean, 1.20) mg/g creatinine (Cn) for 2,5-hexanedione, from 0.10 to 0.43 (mean, 0.19) g/g Cn for methylhippuric acid, and from 0.05 to 2.53 (mean, 0.37) g/g Cn for hippuric acid; estimated concentrations of n-hexane in workplace air ranged from 13 to 100 (mean, 40) ppm. Control subjects were 22 healthy males without exposure to solvents. With eyes open, postural sway with a frequency of 2-4 Hz in solvent workers was significantly larger than that in controls in the anteroposterior direction. With eyes closed, sway with a frequency of 0-1 Hz was significantly larger in solvent workers in the mediolateral and anteroposterior directions. Results of multiple regression analysis showed that with eyes open the 1- to 2-Hz and 2- to 4-Hz sways were related positively to 2,5-hexanedione and inversely with methylhippuric acid. The pattern of changes suggests that the vestibulocerebellar and spinocerebellar afferent systems are asymptomatically affected by n-hexane; the effect of n-hexane on the vestibulocerebellar system is possibly inhibited by xylene.