Bone Resorption and Environmental Exposure to Cadmium in Women: A Population Study

Abstract

Environmental exposure to cadmium decreases bone density indirectly through hypercalciuria resulting from renal tubular dysfunction.
We sought evidence for a direct osteotoxic effect of cadmium in women.
We randomly recruited 294 women (mean age, 49.2 years) from a Flemish population with environmental cadmium exposure. We measured 24-hr urinary cadmium and blood cadmium as indexes of lifetime and recent exposure, respectively. We assessed the multivariate-adjusted association of exposure with specific markers of bone resorption, urinary hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP), as well as with calcium excretion, various calciotropic hormones, and forearm bone density.
In all women, the effect sizes associated with a doubling of lifetime exposure were 8.4% (p=0.009) for HP, 6.9% (p=0.10) for LP, 0.77 mmol/day (p=0.003) for urinary calcium, -0.009 g/cm(2) (p=0.055) for proximal forearm bone density, and -16.8% (p=0.065) for serum parathyroid hormone. In 144 postmenopausal women, the corresponding effect sizes were -0.01223 g/cm(2) (p=0.008) for distal forearm bone density, 4.7% (p=0.064) for serum calcitonin, and 10.2% for bone-specific alkaline phosphatase. In all women, the effect sizes associated with a doubling of recent exposure were 7.2% (p=0.001) for urinary HP, 7.2% (p=0.021) for urinary LP, -9.0% (p=0.097) for serum parathyroid hormone, and 5.5% (p=0.008) for serum calcitonin. Only one woman had renal tubular dysfunction (urinary retinol-binding protein >338 microg/day).
In the absence of renal tubular dysfunction, environmental exposure to cadmium increases bone resorption in women, suggesting a direct osteotoxic effect with increased calciuria and reactive changes in calciotropic hormones.

Full text

Cadmium is a persistent environmental
toxicant (Hogervorst et al. 2007; Lauwerys
and Hoet 2001). Sources of cadmium pollu-
tion are past and present emissions from non-
ferrous industries, waste incineration, use of
cadmium-containing phosphate fertilizers and
sewage sludge, and the burning of fossil fuels
(Lauwerys and Hoet 2001). Human exposure
to cadmium occurs through consumption of
contaminated food or water (Hogervorst et al.
2007; Watanabe et al. 2004) or by inhalation
of tobacco smoke or polluted air (Hogervorst
et al. 2007). Cadmium accumulates in the
human body, in particular in the liver and
kidneys, and has an elimination half-life of
10–30 years (Järup et al. 1998). The urinary
excretion of cadmium over 24 hr is a bio-
marker of lifetime exposure (Järup et al.
1998). Cadmium causes glomerular and tubu-
lar renal dysfunction (Staessen et al. 1994)
and increases calciuria (Staessen et al. 1991).
Current estimates suggest that > 200 mil-
lion people worldwide have osteoporosis and
that the prevalence of this disease is escalating
(Reginster and Burlet 2006). Staessen et al.
(1999) showed that low-level environmental
cadmium exposure promotes osteoporosis and
leads to a higher risk of fractures, especially in
postmenopausal women. Women are at greater
risk of developing cadmium toxicity than are
men (Choudhury et al. 2001). Animal (Wang
et al. 1994) and in vitro (Regunathan et al.
2003) studies suggest that cadmium might
have direct toxic effects on bone, but convinc-
ing evidence for such an effect in humans does
not exist. The development of biochemical
assays that measure pyridinium crosslinks of
collagen, which are specific markers of bone
resorption (McLaren et al. 1992), greatly facili-
tates the exploration of cadmium’s osteotoxic-
ity. In view of the epidemic of osteoporosis
(Reginster and Burlet 2006) and the ubiquitous
distribution of cadmium pollution (Lauwerys
and Hoet 2001), we used urinary crosslinks as a
marker to investigate the possible direct
osteotoxicity of cadmium (over and beyond its
indirect effects on bone via increased calciuria)
(Staessen et al. 1991) in Flemish women living
in districts with low to moderate environmental
cadmium pollution.
Methods
Fieldwork. The Cadmium in Belgium study
(CadmiBel, 1985–1989) (Lauwerys et al.
1990) included 1,107 Flemish participants
randomly recruited from 10 districts in
northeastern Belgium (Staessen et al. 1994).
The participation rate was 78% (Staessen
et al. 1994). The geometric mean cadmium
concentration in the soil sampled from 85
kitchen gardens was 5.3 mg/kg (5th–95th
percentile interval, 1.4–18.9) in six districts,
which bordered on three zinc/cadmium
smelters, and 0.9 mg/kg (0.4–1.6) in four dis-
tricts, which were > 10 km away from the
smelters (Hogervorst et al. 2007). The partic-
ipants of the 10 districts had similar charac-
teristics apart from exposure to cadmium
(Staessen et al. 1994, 1999). We complied
with all applicable requirements of U.S. and
international regulations, in particular the
Helsinki declaration for investigation of
human subjects. The Ethics Review Board of
the Medical Faculty of the University of
Environmental Health Perspectives
•
VOLUME 116 |NUMBER 6 |June 2008
777
Research
Address correspondence to J.A. Staessen, Studie-
coördinatiecentrum, Laboratorium Hypertensie,
Campus Gasthuisberg, Herestraat 49, Box 702,
B-3000 Leuven, Belgium. Telephone: 32-16-34-7104.
Fax: 32-16-34-7106. E-mail: jan.staessen@med.
kuleuven.ac.be
This study would not have been possible without the
voluntary collaboration of participants and their general
practitioners. The municipality of Hechtel-Eksel,
Belgium, gave logistic support. We gratefully acknowl-
edge the expert technical assistance of S. Covens, L.
Custers, M.-J. Jehoul, H. Truyens, and Y. Zhu (Studies
Coordinating Centre, University of Leuven, Belgium).
The International Lead Zinc Research Organization
(ILZRO) supported the study from 25 January 1990
to 24 February 1994. The European Union (grant
LSHM-CT-2006–037093 InGenious HyperCare),
the Fonds voor Wetenschappelijk Onderzoek
Vlaanderen, Ministry of the Flemish Community,
Brussels, Belgium (grants G.0424.03 and G.0575.06),
and the Katholieke Universiteit Leuven, Belgium
(grants OT/99/28, OT/00/25 and OT/05/49) gave
support to the Studies Coordinating Centre.
H.A. Roels was a member of the scientific review
panel (health) for the Voluntary Risk Assessment
Report on Lead and Lead Compounds drafted by
ILZRO (Research Triangle Park, NC, USA), the
European Bio-Research Consultants (EBRC
Consulting GmbH, Hannover, Germany), and the
Lead Development Association International
(LDAint, London, UK) in the framework of the EC
Chemical Bureau Existing Substances Programme.
All other authors declare they have no competing
financial interests.
Received 13 December 2007; accepted 25 February
2008.
Bone Resorption and Environmental Exposure to Cadmium in Women:
A Population Study
Rudolph Schutte,
1,2
Tim S. Nawrot,
1
Tom Richart,
1
Lutgarde Thijs,
1
Dirk Vanderschueren,
3
Tatiana Kuznetsova,
1
Etienne Van Hecke,
4
Harry A. Roels,
5
and Jan A. Staessen
1
1Studies Coordinating Centre, Division of Hypertension and Cardiovascular Rehabilitation Unit, Department of Molecular and
Cardiovascular Research, University of Leuven, Leuven, Belgium; 2Department of Physiology, School for Physiology, Nutrition and
Consumer Sciences, North-West University, Potchefstroom, South Africa; 3Section of Experimental Medicine and Endocrinology,
Department of Experimental Medicine, University of Leuven, Leuven, Belgium; 4Section of Social and Economic Geography, Department
of Geography and Geology, University of Leuven, Leuven, Belgium; 5Industrial Toxicology and Occupational Medicine Unit, Department
of Public Health, Université catholique de Louvain, Brussels, Belgium
BACKGROUND:Environmental exposure to cadmium decreases bone density indirectly through
hypercalciuria resulting from renal tubular dysfunction.
OBJECTIVE:We sought evidence for a direct osteotoxic effect of cadmium in women.
METHODS:We randomly recruited 294 women (mean age, 49.2 years) from a Flemish population
with environmental cadmium exposure. We measured 24-hr urinary cadmium and blood cadmium
as indexes of lifetime and recent exposure, respectively. We assessed the multivariate-adjusted asso-
ciation of exposure with specific markers of bone resorption, urinary hydroxylysylpyridinoline (HP)
and lysylpyridinoline (LP), as well as with calcium excretion, various calciotropic hormones, and
forearm bone density.
RESULTS:In all women, the effect sizes associated with a doubling of lifetime exposure were 8.4%
(p = 0.009) for HP, 6.9% (p = 0.10) for LP, 0.77 mmol/day (p = 0.003) for urinary calcium,
–0.009 g/cm2(p = 0.055) for proximal forearm bone density, and –16.8% (p = 0.065) for serum
parathyroid hormone. In 144 postmenopausal women, the corresponding effect sizes were
–0.01223 g/cm2(p = 0.008) for distal forearm bone density, 4.7% (p = 0.064) for serum calcitonin,
and 10.2% for bone-specific alkaline phosphatase. In all women, the effect sizes associated with a
doubling of recent exposure were 7.2% (p = 0.001) for urinary HP, 7.2% (p = 0.021) for urinary
LP, –9.0% (p = 0.097) for serum parathyroid hormone, and 5.5% (p = 0.008) for serum calcitonin.
Only one woman had renal tubular dysfunction (urinary retinol-binding protein > 338 µg/day).
CONCLUSIONS:In the absence of renal tubular dysfunction, environmental exposure to cadmium
increases bone resorption in women, suggesting a direct osteotoxic effect with increased calciuria
and reactive changes in calciotropic hormones.
KEY WORDS:bone, cadmium, pyridinium crosslinks. Environ Health Perspect 116:777–783 (2008).
doi:10.1289/ehp.11167 available via http://dx.doi.org/ [Online 25 February 2008]

Leuven approved the study. Participants gave
informed consent at recruitment.
From 1991 to 1996, in the framework of
the Public Health and Environmental
Exposure to Cadmium study (PheeCad), we
invited 823 former CadmiBel participants,
who had renewed their informed consent, for
a measurement of bone density, of whom
614 (74.6%) responded. This cohort included
307 women, whose exposure to cadmium was
exclusively environmental. Because of missing
information, we excluded 13 women. Thus,
the study population for the present analysis
consisted of 294 women.
Clinical measurements. As described else-
where (Staessen et al. 1999), from 1991 to
1996 we measured bone density at the fore-
arm just above the wrist by single photon
absorptiometry (ND1100 bone density scan-
ner; Nuclear Data Inc, Schaumburg, IL,
USA). Distal scans of adult forearms traverse
a mean of 35% trabecular bone, whereas in
proximal scans this proportion declines to
nearly 5%. Trained nurses measured the
anthropometric characteristics of the women.
They administered a questionnaire to collect
information about the participants’ lifestyle
and medication intake. Socioeconomic status
was coded and condensed into a scale with
scores ranging from 1 to 3. Using published
tables, we computed the energy spent in phys-
ical activity from body weight, time devoted
to work and sports, and type of physical activ-
ity. Premenopause was defined as an active
menstrual cycle throughout follow-up.
Menopause was defined as the absence or ces-
sation of periods during follow-up, confirmed
by measurement of the serum concentration
of follicle-stimulating hormone (FSH).
Biochemical measurements. At baseline
(1985–1989) and follow-up (1991–1996), the
participants collected a 24-hr urine sample in
a wide-neck polyethylene container for the
measurement of cadmium, calcium, retinol-
binding protein, and creatinine. For these
measurements, we applied the same analyti-
cal methods throughout the study. We meas-
ured serum and urinary creatinine (Bartels
and Böhmer 1971) using an automated enzy-
matic technique (Technicon Autoanalyzer,
Technicon Instruments, Tarrytown, NY,
USA). At follow-up (1991–1996), the nurses
obtained a venous blood sample from the par-
ticipants within 2 weeks of the bone density
measurement. We measured the serum
concentration of FSH (AR FSH Reagent
Kit, Abbott 6C24-20; Louvain-la-Neuve,
Belgium), calcitonin (CT-U.S.-IRMA Kit,
BioSource Europe, Nivelles, Belgium ), and
γ-glutamyltransferase, an index of alcohol
intake, using commercially available kits. We
determined bone-specific serum alkaline phos-
phatase activity on a COBAS-BIO centrifugal
analyzer (Roche Diagnostics, Vilvoorde,
Belgium), serum parathyroid hormone (PTH)
by a two-site immunometric assay (Bouillon
et al. 1990), serum and urinary calcium by
compleximetry, and urinary retinol-binding
protein, a biomarker of renal tubular dysfunc-
tion, by an automated nonisotopic immuno-
assay based on latex particle agglutination
(Lauwerys et al. 1990).
To measure blood and urinary cadmium,
we applied electrothermal atomic absorption
spectrometry with a stabilized-temperature
platform furnace and Zeeman background
correction (Lauwerys et al. 1990). The exter-
nal quality-control program did not show any
time trend in the accuracy of the cadmium
measurements. In the context of this article,
Schutte et al.
778
VOLUME 116 |NUMBER 6 |June 2008
•
Environmental Health Perspectives
Table 1. Characteristics of 294 women.
Characteristic Premenopausal (
n
= 150) Menopausal (
n
= 144)
p
-Value
Anthropometrics
Age (years) 39.1 ± 6.9 59.8 ± 8.8 < 0.0001
Body mass index (kg/m2) 24.9 ± 5.1 27.5 ± 5.8 < 0.0001
Follicle-stimulating hormone (U/L) 3.3 (0.1–18.5) 65.4 (30.0–137.6) < 0.0001
Urinary creatinine (mmol/day) 10.0 ± 2.0 9.0 ± 2.2 < 0.0001
Biomarkers of exposure
Blood cadmium at baseline (nmol/L) 10.2 (2.7–27.6) 11.7 (4.4–32.9) 0.085
Blood cadmium (nmol/L) 6.9 (1.8–23.1) 8.5 (3.6–24.9) < 0.0001
Urinary cadmium at baseline (nmol/day) 6.3 (2.6–18.9) 11.8 (5.0–29.8) < 0.0001
Urinary cadmium (nmol/day) 5.7 (2.0–17.5) 9.8 (4.0–25.1) < 0.0001
Biomarkers of effect
Proximal forearm density (g/cm2) 0.479 ± 0.052 0.405 ± 0.079 < 0.0001
Distal forearm density (g/cm2) 0.363 ± 0.057 0.308 ± 0.067 < 0.0001
HP (nmol/mmol creatinine) 37.9 (21.0–68.1) 46.8 (22.3–91.9) < 0.0001
LP (nmol/mmol creatinine) 7.4 (3.6–17.6) 9.3 (2.6–20.5) 0.0004
Urinary calcium (mmol/day) 3.87 ± 2.03 4.31 ± 2.67 0.29
Serum total calcium (mmol/L) 2.31 ± 0.09 2.35 ± 0.11 0.058
Parathyroid hormone (pmol/L) 0.69 (0.07–2.70) 0.97 (0.07–3.14) 0.005
Calcitonin (nmol/L) 4.53 (2.67–7.96) 6.31 (3.71–10.5) < 0.0001
Bone-alkaline phosphatase (U/L) 25.7 (10.0–64.0) 42.3 (18.0–103.0) < 0.0001
Urinary retinol-binding protein (µg/day) 61.3 (24.9–143.1) 54.9 (24.2–164.8) 0.16
Lifestyle
Physical activity (kcal/day) 562 (1–2,606) 345 (1–2,426) 0.12
Smoking (0, 1) 63 (42.0) 23 (16.0) < 0.0001
Drinking (0, 1) 15 (10.0) 7 (4.9) 0.094
Middle or high socioeconomic status (0, 1) 46 (30.7) 5 (3.5) < 0.0001
Intake of medications
Diuretics (0, 1) 4 (2.7) 30 (20.8) < 0.0001
Oral contraceptives (0, 1) 42 (28.0 ) NA —
Hormonal substitution (0, 1) NA 7 (4.9) —
NA, not applicable. Values are arithmetic mean ± SD, geometric mean (5th–95th percentile interval), or number of women
(%). Unless indicated otherwise, characteristics were measured at the time of the urine collection for crosslinks. To con-
vert nanomoles of cadmium to micrograms, multiply by 0.11241; to convert millimoles of calcium to milligrams, multiply by
40.08; to convert picomoles of parathyroid hormone to nanograms, multiply by 9.428; to convert nanomoles calcitonin to
micrograms, multiply by 3.4176.
Figure 1. The urinary excretion of pyridinium crosslinks as a function of the 24-hr urinary cadmium excre-
tion in 294 women in single regression analysis for (
A
) HP (
r
= 0.23;
p
< 0.0001) and (
B
) LP (
r
= 0.17;
p
=
0.003). The 24-hr urinary cadmium excretion was the average of two urine collections at a median interval
of 6.6 years and reflects lifetime exposure. Solid and dashed lines represent the regression line and the
95% CI boundaries, respectively.
145
74
38
19
10
32.4
13.5
5.8
2.4
0.1
1 3 10 32 100 1 3 10 32 100
Urinary cadmium (nmol/day) Urinary cadmium (nmol/day)
HP (nmol/mmol creatinine)
LP (nmol/mmol creatinine)
AB

we used the average of the 24-hr urinary cad-
mium excretion at baseline (1985–1989) and
follow-up (1991–1996) as a measure of life-
time exposure and the blood cadmium con-
centration at the time of the urine collection
for crosslinks (1991–1996) as a biomarker of
recent exposure.
On the day of the bone density measure-
ment (1991–1996), the participants collected
an exactly timed 4-hr urine sample for the
measurement of the collagen pyridinium
crosslinks, hydroxylysylpyridinoline (HP) and
lysylpyridinoline (LP), and creatinine. We
measured HP and LP by high-performance
liquid chromatography, using a slight modifi-
cation of the methods described by Black
et al. (1998) and Uebelhart et al. (1990). The
intra- and interassay precision was 5.9% and
7.0% for HP, and 9.5% and 10.2% for LP.
The sensitivity of the assay was 1 pmol.
Statistical analyses. For database manage-
ment and statistical analysis, we used SAS soft-
ware (version 9.1; SAS Institute Inc., Cary,
NC, USA). We logarithmically transformed
variables with a non-Gaussian distribution.
We represented the central tendency and
spread of transformed variables by the geomet-
ric mean and the 5th to 95th percentile inter-
val. We compared means and proportions by
use of the large sample z-test and the chi-
square statistic, respectively. We assessed lon-
gitudinal changes in proportions by
McNemar’s test. We compared parity across
subgroups of women by Kruskall–Wallis test.
All p-values refer to two-sided hypotheses.
We plotted mean values of the biomarkers
of effect by quartiles of the exposure measures
to ensure that there was no threshold phe-
nomenon and that linear correlation tech-
niques were appropriate. We investigated
associations between biomarkers of effect and
exposure using single and multiple linear
regressions. We identified covariates by a
stepwise regression procedure with the p-val-
ues for variables to enter and to stay in the
model set at 0.15. Covariates considered for
entry in the model were age, age squared,
body mass index, smoking, γ-glutamyl-
transferase activity in serum, intake of diuret-
ics, use of supplements of calcium and/or
vitamin D, menopausal status, hormone
replacement therapy and/or oral contracep-
tion, parity, energy spent in physical activity,
socioeconomic status, and urinary retinol-
binding protein.
The 5th–95th percentile interval of the
blood cadmium concentration and the 24-hr
urinary cadmium excretion spanned approxi-
mately a 10-fold increase. Because we had
normalized the distributions of blood and uri-
nary cadmium by a logarithmic transforma-
tion, we expressed changes in the biomarkers
of effect as the effect sizes related to a dou-
bling of blood or urinary cadmium. We esti-
mated these responses and their 95%
confidence interval (CI) by multiplying
regression coefficients (± 1.96 ×SE) by 0.3
(the logarithm of 2).
Results
Characteristics of women. The median interval
between baseline and the follow-up examina-
tion was 6.6 years (range, 5.3–10.5 years).
Based on the questionnaires administered at
baseline and follow-up and the measurement
of FSH in serum at follow-up, the study pop-
ulation included 150 premenopausal and 144
menopausal women. Table 1 lists the women’s
characteristics by menopausal status. Age at
enrollment ranged from 20.4 to 73.6 years. As
expected, bone density was lower in
menopausal than in premenopausal women,
whereas the opposite was true for the urinary
excretion of crosslinks. The median time at
which the participants started collecting urine
for the measurement of crosslinks was 1000
hours (interquartile range, 0700–1200 hours).
From baseline to follow-up, blood cad-
mium decreased by 29.5% (95% CI, 24.5 to
34.2%; p < 0.0001), and 24-hr urinary cad-
mium declined by 12.7% (95% CI, 8.0 to
17.2%; p < 0.0001). During follow-up, the
number of women who smoked decreased
(p= 0.003) from 103 (35.0%) to 86 (29.2%).
In smokers, the median daily tobacco use was
15 cigarettes (5th–95th percentile interval,
4–30 cigarettes). During follow-up, no signifi-
cant changes occurred in the prevalence of
alcohol consumption [15 (5.1%) vs. 22 (7.5%)
women; p = 0.13], the energy spent in physical
activity (454 vs. 442 kcal/day; p= 0.90), the
intake of oral contraceptives [43 (14.6%) vs.
42 (14.3%); p= 0.87] or hormone replacement
therapy [3 (1.0%) vs. 7 (2.4%); p= 0.16].
More women used diuretics at the follow-up
examination than at baseline [34 (11.6%)] vs.
25 (8.5%); p= 0.029].
Unadjusted analyses. In single regression
analysis, we noticed positive correlations of
the urinary excretion of HP (r = 0.23;
p< 0.0001) and LP (r= 0.17; p= 0.003) with
the 24-hr excretion of cadmium (Figure 1),
which was mirrored by inverse associations of
proximal (–0.32; p< 0.0001) and distal
(–0.22; p= 0.0001) forearm bone density
with the biomarker of lifetime exposure. In
addition, there was a positive correlation
between the 24-hr urinary excretion of cal-
cium and cadmium (r= 0.19, p= 0.0009).
Adjusted analyses. In exploratory analyses,
we studied the associations of biomarkers of
effect with the 24-hr cadmium excretion across
quartiles with adjustments applied for age, age
squared, and menopausal status (Table 2).
Urinary HP excretion increased significantly
with higher 24-hr cadmium excretion (pfor
trend, 0.028). LP showed the same tendency
(pfor difference between the lowest and high-
est quartile, 0.095). The 24-hr calciuria
increased significantly with higher 24-hr uri-
nary cadmium (pfor trend, 0.0002), with an
opposite trend for PTH (pfor difference
between the lowest and highest quartile, 0.046)
(Table 2). In the minimally adjusted analyses
across quartiles of 24-hr urinary cadmium
excretion, the trends in the serum levels of total
calcium, bone-specific alkaline phosphatase,
and calcitonin did not reach significance.
Bone resorption and cadmium
Environmental Health Perspectives
•
VOLUME 116 |NUMBER 6 |June 2008
779
Table 2. Characteristics of women across quartiles of the 24-hr urinary cadmium excretion
.
Quartiles of the distribution of 24-hr urinary cadmium
p
-Value
Characteristic Low Medium-low Medium-high High For trend For low vs. high
Limits of quartiles (nmol/day) < 5.5 ≥ 5.5– < 8.2 ≥ 8.2– < 11.9 ≥ 11.9
No. 74 73 74 73
Age (years) 37.4 ± 9.8 50.4 ± 12.3 52.0 ± 11.2 57.2 ± 10.0 < 0.0001 < 0.0001
Menopausal 9 (12.2) 36 (49.3) 41 (55.4) 58 (79.5) < 0.0001 < 0.0001
Parity [no. (range)] 2 (0–5) 2 (0–12) 2 (0–8) 2 (0–11) 0.47 0.19
Used food supplements
a
8 (10.8) 11 (15.1) 8 (10.8) 7 (9.6) 0.74 0.24
HP (nmol/mmol creatinine ) 37.6 (22.6–73.4) 41.6 (20.7–74.2) 42.3 (22.8–86.0) 47.5 (23.6–89.5) 0.028 0.003
LP (nmol/mmol creatinine) 7.5 (4.0–15.9) 8.6 (3.5–16.3) 8.2 (2.5–20.0) 9.1 (2.2–19.8) 0.37 0.095
Urinary calcium (mmol/day) 3.09 ± 4.18 3.76 ± 3.47 3.70 ± 3.53 5.83 ± 3.74 0.0002 0.0002
Serum calcium (mmol/L) 2.32 ± 0.12 2.35 ± 0.10 2.33 ± 0.10 2.32 ± 0.11 0.30 0.79
Bone-alkaline phosphatase (U/L) 33.0 (16.4–74.1) 29.7 (9.5–65.8) 35.1 (14.9–87.1) 33.9 (13.5–94.6) 0.32 0.81
Parathyroid hormone (pmol/L) 0.96 (0.11–2.52) 0.91 (0.07–3.49) 0.81 (0.07–3.33) 0.63 (0.07–2.35) 0.13 0.046
Calcitonin (nmol/L) 5.15 (2.82–8.61) 5.22 (2.74–9.17) 5.39 (2.98–9.12) 5.56 (3.28–10.4) 0.64 0.26
Values are arithmetic mean ± SD, geometric mean (5th–95th percentile interval), or number of women (%).
a
Calcium and/or vitamin D.

The independent associations between the
effect biomarkers and the index of lifetime
exposure are shown in Tables 3 and 4. With
adjustments applied for the significant covari-
ates, which were identified by stepwise regres-
sion, a doubling of the urinary cadmium
excretion was associated with increases in the
urinary excretion of HP and LP, and in 24-hr
urinary calcium amounting to 8.4% (95% CI,
2.1 to 15.0%; p = 0.009), 6.9% (95% CI, –1.9
to 16.4%; p= 0.10), and 0.77 mmol/day (95%
CI, 0.27 to 1.27 mmol/day; p= 0.003), respec-
tively. In all women, doubling of urinary cad-
mium excretion was associated with small
decreases in the proximal bone density
(–0.00903 g/cm
2
; 95% CI, –0.00014 to
0.01819 g/cm
2
; p= 0.055) and in the serum
concentration of PTH (–16.8%; 95% CI,
–37.5 to 0.9%; p= 0.065). In menopausal
women, the effect sizes associated with a dou-
bling of 24-hr urinary cadmium were –0.01223
g/cm
2
(95% CI, –0.00322 to –0.02123 g/cm
2
;
p= 0.008) for the distal forearm bone density,
4.7% (95% CI, –0.3 to 9.9%; p= 0.064) for
serum calcitonin, and 10.2% (95% CI, 1.4 to
19.7%; p= 0.023) for the activity in serum of
bone-specific alkaline phosphatase.
The independent associations between the
effect biomarkers and the index of current
exposure appear in Tables 5 and 6. For each
effect biomarker, we adjusted these relations
for the same covariates as in Tables 3 and 4.
In all women, the effect sizes associated with a
doubling of blood cadmium concentration
were 7.2% (95% CI, 2.9 to 11.6%; p=
0.001) for urinary HP, 7.2% (95% CI, 1.1 to
13.7%; p= 0.021) for urinary LP, –9.0%
(95% CI, –18.5 to 1.7%; p = 0.097) for
serum PTH, and 5.5% (95% CI, 1.5 to
9.8%; p= 0.008) for serum calcitonin. In
postmenopausal women, doubling of the
blood cadmium concentration was associated
with a decrease in distal forearm bone density
and an increase in bone-specific alkaline phos-
phatase activity. The effect sizes were
–0.00870 g/cm
2
(95% CI, –0.01693 to
–0.00047 g/cm
2
; p= 0.038) and 7.0% (95%
CI, –1.1 to 15.7%; p= 0.091).
Sensitivity analyses. In all women but
one, the urinary excretion of retinol-binding
protein was below the cut-off value for early
renal tubular dysfunction (≥338 µg/day)
(Buchet et al. 1990). The urinary excretion of
retinol-binding protein, socioeconomic status,
the use of food supplements containing cal-
cium and/or vitamin D, and parity did not
enter any regression model. After forcing
these four additional independent variables
into our regression models, our findings
remained consistent. In all women, the effect
sizes associated with a doubling of 24-hr uri-
nary cadmium were 8.2% (95% CI, 1.7 to
15.1%; p= 0.013) for HP, 6.5% (95% CI,
–2.5 to 16.3%; p= 0.16) for urinary LP, 0.87
mmol/day (95% CI, 0.35 to 1.38 mmol/day;
p= 0.001) for 24-hr urinary calcium, and
–19.7% (95% CI, –41.5 to –1.3%; p=
0.035) for serum PTH. In all women, the
estimates associated with a doubling of blood
cadmium were 7.3% (95% CI, 2.9 to 11.9%;
p= 0.001) for HP, 7.6% (95% CI, 1.2 to
14.3%; p= 0.019) for LP, –0.3% (95% CI,
–7.1 to 7.4%; p= 0.96) for serum PTH, and
5.9% (95% CI, 1.7 to 10.2%; p= 0.006) for
serum calcitonin. With these additional
adjustments applied, in menopausal women,
distal forearm bone density decreased by
0.01241 g/cm
2
(95% CI, 0.00335 to 0.02147
g/cm
2
; p= 0.008) and by 0.00902 g/cm
2
(95% CI, 0.00053 to 0.01752 g/cm
2
; p=
0.038) for a doubling in urinary and blood
cadmium, respectively.
Our findings also remained consistent
when we separately used the 24-hr urinary
excretion of cadmium either at baseline or at
follow-up as index of lifetime exposure and
when we additionally adjusted for the time of
day, at which participants collected urine for
the measurement of HP and LP (data not
shown).
Schutte et al.
780
VOLUME 116 |NUMBER 6 |June 2008
•
Environmental Health Perspectives
Table 3. Independent associations of forearm bone density and effect biomarkers in urine with lifetime exposure as reflected by 24-hr cadmium excretion.
Forearm bone density Biomarkers in urine
Proximal (g/cm2) Distal (g/cm2) HP (log nmol/mmol creatinine) LP (log nmol/mmol creatinine) Calcium (mmol/day)
R
2 0.454 0.371 0.206 0.128 0.066
Intercept 0.278 0.161 1.990 1.253 0.399
Partial regression coefficients (± SE)
Urinary cadmium (log nmol/day) –0.030 ± 0.016* NS 0.116 ± 0.044#0.096 ± 0.063* 2.568 ± 0.846#
Menopause (0, 1) NS NS NS NS NS
Urinary cadmium ×menopause NS –0.041 ± 0.015#NS NS NS
Age (years ×10–1) 0.087 ± 0.012## 0.070 ± 0.020## –0.267 ± 0.059## –0.267 ± 0.084#NS
Age squared (years2×10–3) –0.115 ± 0.019## 0.091 ± 0.19## 0.286 ± 0.055## 0.298 ± 0.078#NS
Body mass index (kg/m2×10–1) NS NS 0.069 ± 0.019## 0.048 ± 0.026* NS
γ-glutamyltransferase (log U/L) 0.041 ± 0.013#0.054 ± 0.013## –0.064 ± 0.038* NS NS
Use of diuretics (0, 1) NS NS NS –0.143 ± 0.047#–1.798 ± 0.669#
Physical activity (log kcal/day ×10–1) 0.050 ± 0.029* NS NS NS NS
Significance of the partial regression coefficients: NS, not significant; *0.1 <
p
< 0.05; ##
p
≤0.001. Socioeconomic position and the 24-hr excretion of retinol-binding protein did not enter
any model.
Table 4. Independent associations of effect biomarkers in serum with lifetime exposure as reflected by 24-hr cadmium excretion.
Calcium (mmol/L) Parathyroid hormone (log pmol/L) Calcitonin (log nmol/L) Bone-specific alkaline phosphatase (log U/L)
R
20.045 0.083 0.388 0.301
Intercept 2.376 –0.814 1.226 1.921
Partial regression coefficients (± SE)
Urinary cadmium (log nmol/day) NS –0.224 ± 0.121* NS NS
Menopause (0, 1) 0.035 ± 0.014** NS 0.096 ± 0.039** 1.151 ± 0.061**
Urinary cadmium ×menopause NS NS 0.066 ± 0.036* 0.140 ± 0.061**
Age (years ×10–1) NS NS –0.119 ± 0.047** NS
Age squared (years2×10–3) NS NS 0.120 ± 0.044#NS
Body mass index (kg/m2×10–1) –0.0239 ± 0.011** 0.086 ± 0.048* –0.033 ± 0.015** NS
γ-glutamyltransferase (log U/L) NS NS –0.179 ± 0.030## –0.312 ± 0.052##
Smoking (0, 1) NS –0.104 ± 0.061* NS NS
Physical activity (log kcal/day ×10–1) NS NS NS –0.308 ± 0.011#
Use of diuretics (0, 1) NS NS –0.067 ± 0.026** –0.119 ± 0.044#
Intake of female hormones (0,1) NS NS –0.074 ± 0.021## NS
Significance of the partial regression coefficients: NS, not significant; *0.1 <
p
< 0.05; **
p
≤0.05; #
p
≤0.01; ##
p
≤0.001. Socioeconomic position and the 24-hr excretion of retinol-binding
protein did not enter any model.

Discussion
Population-based studies from Belgium
(Staessen et al. 1999), Sweden (Åkesson et al.
2006; Alfvén et al. 2000; Järup and Alfvén
2004), Japan (Honda et al. 2003), and China
(Zhu et al. 2004) showed an association
between osteoporosis and low-level environ-
mental cadmium exposure. The interpretation
of these findings was that cadmium-induced
renal tubular damage (Buchet et al. 1990;
Staessen et al. 1994) attenuated the calcium
reabsorption in the nephron, resulting in
hypercalciuria (Staessen et al. 1994) and dem-
ineralization of bones (Järup and Alfvén
2004; Staessen et al. 1999), particularly in
menopausal women (Staessen et al. 1999). In
keeping with experimental studies, the present
study supports the interpretation that, in
women, cadmium decreases bone density
through a direct osteotoxic effect. Indeed, we
found consistent associations between bio-
markers of bone resorption, the urinary pyri-
dinium crosslinks HP and LP, and biomarkers
of lifetime and recent exposure to cadmium.
In addition, serum PTH levels decreased with
higher cadmium exposure, as might be
expected when a toxic substance induces
release of calcium from bone tissue. If the
hypercalciuria in cadmium-exposed subjects
were attributed entirely to excessive calcium
loss in the renal tubules, one would expect
instead an increase in PTH with higher expo-
sure to compensate for the urinary calcium
loss. A possible adaptive response favoring
bone formation might occur, especially in
postmenopausal women, with serum levels of
bone-specific alkaline phosphatase activity and
calcitonin correlating positively with cadmium
exposure, as observed in the present study.
To our knowledge, only one previous
population study has addressed the possible
association between bone resorption and low-
level cadmium exposure. In 820 Swedish
women 53–64 years of age, Åkesson and col-
leagues (2006) measured forearm bone min-
eral density, calciotropic hormones, and the
urinary LP concentration not standardized for
creatinine. They assessed exposure to cad-
mium, not from the 24-hr urinary excretion,
but from the concentration in fresh urine
samples and blood. The median values were
4.6 nmol/L (0.52 µg/L) and 3.4 nmol/L
(0.38 µg/L), respectively. In our current
study, the corresponding concentrations in
urine and blood were 5.2 nmol/L (0.58 µg/L)
and 8.0 nmol/L (0.90 µg/L). In multivariate-
adjusted analyses, Åkesson et al. (2006)
reported inverse associations (p< 0.05) of
bone density and serum PTH with the uri-
nary cadmium concentration and a positive
relation between urinary LP and cadmium.
These associations persisted in never-smokers,
who had the lowest, mainly dietary, cadmium
exposure. For LP, there was a significant
interaction between menopause and urinary
cadmium. The associations with blood cad-
mium were not significant in the Åkesson
et al. study, except for PTH.
Laboratory studies strongly support the
epidemiologic evidence for a direct osteotoxic
effect of cadmium. In experimental animals
exposed to cadmium, bone demineralization
begins early after the start of cadmium expo-
sure, well before the onset of kidney damage
(Wilson and Bhattacharyya 1997). In cultures
of bone marrow cells, cadmium accelerated the
differentiation of new osteoclasts from their
progenitor cells and enhanced the activity of
mature osteoclasts (Wilson et al. 1996). In
female mice, bilateral ovariectomy enhanced
the osteotoxicity of cadmium (Comelekoglu
et al. 2007). However, at the molecular level,
the effects of cadmium on bone tissue need
further clarification. Cadmium stimulated
bone resorption by the up-regulation of the
production of prostaglandin E
2
in osteoblasts
through enhanced expression of phospholipase
A
2
and cyclooxygenase (Miyahara et al. 1992).
Exposure of human osteoblast-like cells to
cadmium also produced an increase in cas-
pase-3 activity and nuclear changes character-
istic of apoptosis, including marginalization
and condensing of chromatin and DNA frag-
mentation (Coonse et al. 2007). Experiments
in genetically engineered mice suggested that
the effects of cadmium on bone tissue require
c-Src (Regunathan et al. 2002) and might be
mediated via a p38 mitogen-activated phos-
phokinase pathway (Regunathan et al. 2003),
but are independent from c-Fos expression
(Regunathan et al. 2002).
Our findings might have important impli-
cations for environmental policies, especially
those designed to protect women’s health.
Roughly, 200 million people worldwide suffer
from osteoporosis (Reginster and Burlet
2006). In the United States, there are an esti-
mated 44 million osteoporosis patients, of
whom 30 million are women (Reginster and
Burlet 2006). After menopause, osteoporosis
occurs at an accelerated rate. The studies in
Belgium (Staessen et al. 1999) and China
(Zhu et al. 2004) demonstrated loss of bone
mineral density in relation to cadmium expo-
sure, which was more severe in women
(Staessen et al. 1999; Zhu et al. 2004), partic-
ularly after the onset of menopause (Staessen
et al. 1999). Itai-Itai disease in Japan, an
advanced stage of cadmium-induced osteoma-
lacia and osteoporosis combined with kidney
disease, occurs almost exclusively in older
women (Vahter et al. 2007). Women have a
higher body burden of cadmium than men
(Vahter et al. 2007). Low iron stores that are
common during pregnancy and before
menopause lead to an upregulation of the
duodenal metal transporter, which has a high
affinity for cadmium (Tallkvist et al. 2000;
Vahter et al. 2007). In twin studies, the
Bone resorption and cadmium
Environmental Health Perspectives
•
VOLUME 116 |NUMBER 6 |June 2008
781
Table 5. Independent associations of forearm bone density and effect biomarkers in urine with current exposure as reflected by blood cadmium.
Forearm bone density Biomarkers in urine
Proximal (g/cm2) Distal (g/cm2) HP (log nmol/mmol creatinine) LP (log nmol/mmol creatinine) Calcium (mmol/day)
R
2 0.446 0.358 0.216 0.139 0.042
Intercept 0.300 0.168 1.847 1.193 1.411
Partial regression coefficients (± SE)
Blood cadmium (log nmol/L) NS NS 0.100 ± 0.030## 0.100 ± 0.043** NS
Menopause (0, 1) NS NS NS NS NS
Blood cadmium ×menopause NS –0.029 ± 0.014** NS NS NS
Significance of the partial regression coefficients: NS, not significant; **
p
< 0.05; ##
p
< 0.001. All models were adjusted for the same covariates as in Table 3.
Table 6. Independent associations of effect biomarkers in serum with current exposure as reflected by blood cadmium.
Calcium (mmol/L) Parathyroid hormone (log pmol/L) Calcitonin (log nmol/L) Bone-specific alkaline phosphatase (log U/L)
R
20.046 0.068 0.397 0.300
Intercept 2.383 –0.756 1.186 1.933
Partial regression coefficients (± SE)
Blood cadmium (log nmol/L) NS –0.136 ± 0.082* 0.078 ± 0.029#NS
Menopause (0, 1) 0.034 ± 0.013#NS 0.152 ± 0.025#0.187 ± 0.056##
Blood cadmium ×menopause NS NS NS 0.098 ± 0.058*
Significance of the partial regression coefficients: NS, not significant; *0.1 <
p
< 0.05; #
p
≤0.01; ##
p
≤0.001. All models were adjusted for the same covariates as in Table 4.

heritability of the blood cadmium concentra-
tion was 65% in nonsmoking women, but
only 13% in nonsmoking men (Björkman
et al. 2000). Finally, experimental studies
showed stronger effects of cadmium on cal-
ciotropic hormones and on the metabolism of
calcium and phosphate in female than in male
rats (Brzóka and Moniuszko-Jakoniuk 2005).
The present study has limitations and
strengths. Although our results were consistent
after multiple adjustments and in sensitivity
analyses, we cannot exclude residual con-
founding. We replicated the findings of
Åkesson et al. (2006), albeit at higher exposure
levels. However, the Swedish investigators
measured LP and cadmium in concentration
units on the same spot urine sample. We
measured the crosslinks standardized to crea-
tinine and 24-hr cadmium excretion on dif-
ferent samples, and we therefore excluded the
possibility of a spurious association due to
varying degrees of the concentration of urine
in individual samples. Moreover, we also
found significant dose–effect associations with
blood cadmium, which with the exception of
PTH was not the case in the Swedish study
(Åkesson et al. 2006). Some experts consider
LP as a more specific marker of bone resorp-
tion than HP (Robins 1983). However, both
LP and HP originate from mature collagen.
In most circumstances, bone collagen degra-
dation is the major contributor to both
crosslink compounds in urine, due to the low
turnover rate of other tissues (McLaren et al.
1992). The urinary excretion of pyridinium
crosslinks has a diurnal variation, with levels
peaking in the morning (Schlemmer et al.
1992). Our results were consistent when we
accounted for the starting time of the urine
collection.
Cadmium is a ubiquitous and persistent
environmental contaminant. In our study,
zinc smelters began to emit cadmium into the
atmosphere in 1888. The last zinc smelter
shut down in 2002. Even though annual
emissions dropped from 125,000 kg in 1950
to 130 kg in 1989, the historical pollution of
the soil remains a source of exposure via food
contamination and the inhalation of house
dust (Hogervorst et al. 2007). In the United
States, ecologic studies demonstrated cad-
mium pollution, not only close to industrial
(Gale et al. 2004) or mining (Peplow and
Edmonds 2004) settlements, but in agricul-
tural (Schmitt et al. 2006) and coastal
(Karouna-Renier et al. 2007) areas as well.
Japanese women remain currently more
exposed to cadmium than other rice-depen-
dent populations in Asia and other parts of the
world (Watanabe et al. 2004). Satarug and
Moore (2004) predicted that the continuing
mobilization of cadmium from once non-
bioavailable geologic matrices into biologically
accessible materials could gradually increase
over the next 10–20 years and amplify the
upward trend in osteoporosis in aging popula-
tions worldwide. Globally, in 2000, there were
an estimated 9.0 million osteoporotic fractures
(Johnell and Kanis 2006). These fractures
caused the loss of 5.8 million disability-
adjusted life-years, of which 51% occurred in
Europe and the Americas (Johnell and Kanis
2006). Cadmium is also nephrotoxic (Staessen
et al. 1994) and increases the risk of lung can-
cer (Nawrot et al. 2006). Regulators must real-
ize that because of these health effects and the
very long biological half-life of cadmium
(Järup et al. 1998), exposure due to human
activities is unacceptable.
In conclusion, cadmium is an osteotoxic
pollutant that increases bone resorption. Even
in the absence of cadmium-induced renal
tubular dysfunction, low-level environmental
exposure to cadmium increases calciuria with
reactive changes in calciotropic hormones.
The provisional tolerable daily intake of cad-
mium via food is currently 1 µg/kg per day
(Nordberg 2004). The question arises
whether, in the light of the present findings
and the disability associated with osteoporotic
fractures in aging populations (Johnell and
Kanis 2006), regulators should not lower this
threshold, particularly for women.
REFERENCES
Åkesson A, Bjellerup P, Lundh T, Lidfeldt J, Nerbrand C,
Samsioe G, et al. 2006. Cadmium-induced effects on bone
in a population-based study of women. Environ Health
Perspect 114:830–834.
Alfvén T, Elinder CG, Carlsson MD, Grubb A, Hellström L,
Presson B, et al. 2000. Low level cadmium exposure and
osteoporosis. J Bone Miner Res 15:1579–1586.
Bartels H, Böhmer M. 1971. Ein Mikromethode zur Kreatinin
Bestimmung [in German]. Clin Chem Acta 32:81–85.
Björkman L, Vahter M, Pedersen NL. 2000. Both the environ-
ment and genes are important for concentrations of cad-
mium and lead in blood. Environ Health Perspect
108:719–722.
Black D, Duncan A, Robins SP. 1998. Quantitative analysis of
the pyridinium crosslinks of collagen in urine using ion-
paired reversed-phase high-performance liquid chro-
matography. Anal Biochem 169:197–203.
Bouillon R, Coopmans W, Degroote DEH, Radoux D, Eliard PH.
1990. Immunoradiometric assay of parathyrin with poly-
clonal and monoclonal region specific antibodies. Clin
Chem 36:271–276.
Brzóka MM, Moniuszko-Jakoniuk J. 2005. Effect of low-level
lifetime exposure to cadmium on calciotropic hormones in
aged femal rats. Arch Toxicol 79:636–646.
Buchet JP, Lauwerys R, Roels H, Bernard A, Bruaux P, Claeys
F, et al. 1990. Renal effects of cadmium body burden of the
general population. Lancet 336:699–702.
Choudhury H, Harvey T, Thayer WC, Lockwood TF, Stiteler
WM, Goodrum PE, et al. 2001. Urinary cadmium elevation
as a biomarker of exposure for evaluating a cadmium
dietary exposure biokinetic model. J Toxicol Environ
Health Part A 63:321–350.
Comelekoglu U, Yalin S, Bagis S, Ogenler O, Sahin NO, Yildir A,
et al. 2007. Low-exposure cadmium is more toxic on osteo-
porotic rat femoral bone: mechanical, biochemical, and
histopathological evaluation. Ecotoxicol Environ Saf
66:267–271.
Coonse KG, Coonts AJ, Morrison EV, Heggland SJ. 2007.
Cadmium induces apoptosis in the human osteoblast-like
cell line Saos-2. J Toxicol Environ Health 70:575–581.
Gale NL, Adams CD, Wixson BG, Loftin KA, Huang YW. 2004.
Lead, zinc, copper, and cadmium in fish and sediments
from the Big River and Flat River Creek of Missouri’s old
lead belt. Environ Geochem Health 26:37–49.
Hogervorst J, Plusquin M, Vangronsveld J, Nawrot T, Cuypers
A, Van Hecke E, et al. 2007. House dust as possible route
of environmental exposure to cadmium and lead in the
adult general population. Environ Res 103:30–37.
Honda R, Tsuritani I, Noborisaka Y, Suzuki H, Ishizaki M,
Yamada Y. 2003. Urinary cadmium excretion is correlated
with calcaneal bone mass in Japanese women living in an
urban area. Environ Res 91:63–70.
Järup L, Alfvén T. 2004. Low level cadmium exposure, renal and
bone effects—the OSCAR study. Biometals 17:505–509.
Järup L, Berglund M, Elinder CG, Nordberg G, Vahter M. 1998.
Health effects of cadmium exposure–a review of the
literature and a risk estimate. Scand J Work Environ
Health 24(suppl 1):1–51.
Johnell O, Kanis JA. 2006. An estimate of the worldwide preva-
lence and disability associated with osteoporotic frac-
tures. Osteoporosis Int 17:1726–1733.
Karouna-Renier NK, Snyder RA, Allison JG, Wagner MG,
Ranga RK. 2007. Accumulation of organic and inorganic
contaminants in shellfish collected in estuarine waters
near Pensacola, Florida: contamination profiles and risks
to human consumers. Environ Pollution 145:474–488.
Lauwerys R, Amery A, Bernard A, Bruaux P, Buchet JP, Claeys
F, et al. 1990. Health effects of environmental exposure to
cadmium: objectives, design and organization of the
Cadmibel study: a cross-sectional morbidity study carried
out in Belgium from 1985 to 1989. Environ Health Perspect
87:283–289.
Lauwerys RR, Hoet P. 2001. Biological monitoring of exposure
to inorganic and organometallic substances. Cadmium. In:
Industrial Chemical Exposure. Guidelines for Biochemical
Monitoring. 3rd ed. Washinghton, DC:Lewis Publishers,
54–68.
McLaren AM, Hordon LD, Bird HA, Robins SP. 1992. Urinary
excretion of pyridinium crosslinks of collagen in patients
with osteoporosis and the effects of bone fracture. Ann
Rheum Dis 51:648–651.
Miyahara T, Takata M, Mori-Uchi S, Miyata M, Nagai M,
Sugure A, et al. 1992. Stimulative effects of cadmium on
bone resorption in neonatal parietal bone resorption.
Toxicology 73:93–99.
Nawrot T, Plusquin M, Hogervorst J, Roels HA, Celis H, Thijs L,
et al. 2006. Environmental exposure to cadmium and risk of
cancer: a prospective population-based study. Lancet
Oncol 7:119–126.
Nordberg M. 2004. Environmental exposure and preventive
measures in Sweden and EU. Biometals 17:589–592.
Peplow D, Edmonds R. 2004. Health risks associated with cont-
amination of groundwater by abandoned mines near
Twisp in Okanogan County, Washington, USA. Environ
Geochem Health 26:69–79.
Reginster JY, Burlet N. 2006. Osteoporosis: a still increasing
prevalence. Bone 38:S4–S9.
Regunathan A, Cerny EA, Villarreal J, Bhattacharyya MH. 2002.
Role of
fos
and
src
in cadmium-induced decreases in
bone mineral content in mice. Toxicol Appl Pharmacol
185:25–40.
Regunathan A, Glesne DA, Wilson AK, Song J, Nicolae D,
Flores T, et al. 2003. Microarray analysis of changes in
bone cell gene expression early after cadmium gavage in
mice. Toxicol Appl Pharmacol 191:272–293.
Robins SP. 1983. Cross-linking of collagen. Isolation, structural
characterization and glycosylation of pyridinoline.
Biochem J 215:167–173.
Satarug S, Moore MR. 2004. Adverse health effects of chronic
exposure to low-level cadmium in foodstuffs and cigarette
smoke. Environ Health Perspect 112:1099–1103.
Schlemmer A, Hassager C, Jensen SB, Christiansen C. 1992.
Marked diurnal variation in urinary excretion of pyridinium
cross-links in premenopausal women. J Clin Endocrinol
Metab 74:476–480.
Schmitt CJ, Brumbaugh WG, Linder GL, Hinck JE. 2006. A
screening-level assessment of lead, cadmium, and zinc in
fish and crayfish from Northeastern Oklahoma, USA.
Environ Geochem Health 28:445–471.
Staessen J, Amery A, Bernard A, Bruaux P, Buchet JP, Claeys
F, et al. 1991. Effects of exposure to cadmium on calcium
metabolism: a population study. Br J Ind Med 45:710–714.
Staessen JA, Lauwerys RR, Ide G, Roels HA, Vyncke G, Amery
A. 1994. Renal function and historical environmental cad-
mium pollution from zinc smelters. Lancet 343:1523–1527.
Schutte et al.
782
VOLUME 116 |NUMBER 6 |June 2008
•
Environmental Health Perspectives

Staessen JA, Roels HA, Emelianov D, Kuznetsova T, Thijs L,
Vangronsveld J , et al. 1999. Environmental exposure to
cadmium, forearm bone density, and risk of fractures:
prospective population study. Lancet 353:1140–1144.
Tallkvist J, Bowlus CL, Lönnerdal B. 2000.
DMT1
gene expres-
sion and cadmium absorption in human absorptive entero-
cytes. Toxicol Lett 122:171–177.
Uebelhart D, Gineyts E, Chaouy MC, Delmas PD. 1990. Urinary
excretion of pyridinium crosslinks: a new marker of bone
resorption in metabolic bone disease. Bone Miner 8:87–96.
Vahter M, Åkesson A, Lidén C, Ceccatelli S, Berglund M. 2007.
Gender differences in the disposition and toxicity of
metals. Environ Res 104:85–95.
Wang C, Brown S, Bhattacharyya MH. 1994. Effect of cadmium
on bone calcium and 45Ca in mouse dams on a calcium-
deficient diet: evidence of Itai-Itai-like syndrome. Toxicol
Appl Pharmacol 127:320–330.
Watanabe T, Zhang ZW, Moon CS, Shimbo S, Nakatsuka H,
Matsuda-Inoguchi N, et al. 2004. Cadmium exposure of
women in general populations in Japan during 1991–1997
compared with 1977–1981. Int Arch Occup Environ Health
73:26–34.
Wilson AK, Bhattacharyya MH. 1997. Effects of cadmium on
bone: an in vivo model for the early response. Toxicol Appl
Pharmacol 145:68–73.
Wilson AK, Cerny EA, Smith BD, Wagh A, Bhattacharyya MH.
1996. Effects of cadmium on osteoclast formation and
activity
in vitro
. Toxicol Appl Pharm 140:451–460.
Zhu G, Wang H, Shi Y, Weng S, Jin T, Kong Q, et al. 2004.
Environmental cadmium exposure and forearm bone den-
sity. Biometals 17:499–503.
Bone resorption and cadmium
Environmental Health Perspectives
•
VOLUME 116 |NUMBER 6 |June 2008
783