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Polyfluoroalkyl Chemicals and Menopause among Women 20–65 Years of Age (NHANES)

Office of Health Assessment and Translation, Division of the National Toxicology Program, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, North Carolina, USA
Environmental Health Perspectives (Impact Factor: 7.98). 11/2013; 122(2). DOI: 10.1289/ehp.1306707
Source: PubMed

ABSTRACT

Polyfluoroalkyl chemicals (PFCs) such as perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) have been associated with early menopause. However, previous cross sectional studies have lacked adequate data to investigate possible reverse causality, i.e., higher serum concentrations due to decreased excretion after menopause.
We investigate the association between PFOS, PFOA, perfluorononanoate (PFNA), and perfluorohexane sulfonate (PFHxS) and age at natural menopause among women ages 20-65 in NHANES.
We used proportional hazard models to estimate hazard ratios (HR) for the onset of natural menopause as a function of age and serum PFC levels, and to investigate reverse causation by estimating associations between PFC levels and rate of hysterectomy. We also used multivariable linear regression to determine whether time since menopause predicted serum PFC levels.
After adjusting for age at survey, race/ethnicity, education, ever smoking, and parity, women with higher levels of PFCs had earlier menopause compared to women with the lowest levels. We observed a monotonic association with PFHxS: the HR was 1.42 (95% CI: 1.08, 1.87) for serum concentrations in the 2(nd) vs. 1(st) tertile, and 1.70 (95% CI: 1.36, 2.12) for the 3(rd) vs. 1(st) tertile. We also found evidence of reverse causation: PFCs were positively associated with rate of hysterectomy, and time since natural menopause was positively associated with serum PFCs.
Our findings suggest a positive association between PFCs and menopause; however, at least part of the association may be due to reverse causation. Regardless of underlying cause, women appear to have higher PFC concentrations after menopause.

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Research
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Polyfluoroalkyl Chemicals and Menopause among Women 20–65 Years of Age
(NHANES)
Kyla W. Taylor,
1
Kate Hoffman,
2
Kristina A. Thayer,
1
and Julie L. Daniels
2
1
Office of Health Assessment and Translation, Division of the National Toxicology Program, National Institute of Environmental Health
Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, North Carolina, USA;
2
University of North Carolina Gillings School of Global Public Health, Chapel Hill, North Carolina, USA
Background: Polyfluoroalkyl chemicals (PFCs) such as perfluorooctane sulfonate (PFOS) and
perfluoro octanoate (PFOA) have been associated with early menopause. However, previous cross-
sectional studies have lacked adequate data to investigate possible reverse causality (i.e., higher
serum concentrations due to decreased excretion after menopause).
oBjectives: We investigated the association between PFOS, PFOA, perfluorononanoate (PFNA),
and perfluorohexane sulfonate (PFHxS) and age at natural menopause among women 20–65 years
of age in NHANES (National Health and Nutrition Examination Survey).
Methods: We used proportional hazard models to estimate hazard ratios (HRs) for the onset of
natural menopause as a function of age and serum PFC levels, and to investigate reverse causation
by estimating associations between PFC levels and the rate of hysterectomy. We also used multi-
variable linear regression to determine whether time since menopause predicted serum PFC levels.
results: After adjusting for age at survey, race/ethnicity, education, ever smoking, and parity,
women with higher levels of PFCs had earlier menopause than did women with the lowest PFC
levels. We observed a monotonic association with PFHxS: e HR was 1.42 (95% CI: 1.08, 1.87)
for serum concentrations in tertile 2 versus tertile 1, and 1.70 (95% CI: 1.36, 2.12) for tertile 3
versus tertile 1. We also found evidence of reverse causation: PFCs were positively associated with
rate of hysterectomy, and time since natural menopause was positively associated with serum PFCs.
conclusions: Our findings suggest a positive association between PFCs and menopause; however,
at least part of the association may be due to reverse causation. Regardless of underlying cause,
women appear to have higher PFC concentrations after menopause.
citation: Taylor KW, Hoffman K, Thayer KA, Daniels JL. 2014. Polyfluoroalkyl chemicals
and meno pause among women 20–65 years of age (NHANES). Environ Health Perspect
122:145–150; http://dx.doi.org/10.1289/ehp.1306707
Introduction
Polyfluoroalkyl chemicals (PFCs) are man-
made compounds that have been used in a
number of common consumer and industrial
products such as food containers; stain- and
water-resistant protection for clothing, furni-
ture, and carpets; paints; fire-fighting foam;
and photographic emulsifiers (Lau et al.
2007). PFCs are ubiquitously present and per-
sistent in the environment (Lau et al. 2007),
and although there are demographic, geo-
graphic, and temporal differences, exposures
in the general population are widespread.
Four PFC analytes—perfluoro octane sulfo-
nate (PFOS), perfluoro octanoate (PFOA),
perfluoro nonanoate (PFNA), and perfluoro-
hexane sulfonate (PFHxS)—are commonly
detected in humans (Calafat et al. 2006;
Fromme 2007; Kato et al. 2011). Unlike
traditional persistent organic pollutants,
which are lipophilic and stored primarily in
fat tissue, PFOS and PFOA are both lipo-
phobic and hydrophobic. After absorption,
they persist in the body by forming chemi-
cal bonds to proteins in serum, rather than
accumulating in lipids (Jones et al. 2003;
Organisation for Economic Co-operation and
Development 2002). Serum levels of PFCs
reflect long-term exposures to these contami-
nants [U.S. Environmental Protection Agency
(EPA) 2012b], with estimated geometric
mean half-lives of 7.3 years (95% CI: 5.8, 9.2)
for PFHxS, 4.8 years (95% CI: 4.0, 5.8) for
PFOS, and 3.5 years (95% CI: 3.0, 4.1) for
PFOA (Olsen et al. 2007). However, in a
more recent study, Bartell et al. (2010) esti-
mated a shorter median half-life for serum
PFOA (2.3 years; 95% CI: 2.1, 2.4).
PFCs are potential endocrine disruptors,
and effects of PFOS and PFOA on endo-
crine function have been reported in animal
studies (Jensen and Leffers 2008; Zhao et al.
2010). Less is known about associations
between PFCs and human endocrine func-
tion. Melzer et al. (2010) reported that higher
concentrations of serum PFOA and PFOS
were associated with current thyroid disease
based on NHANES (National Health and
Nutrition Examination Survey) data from
1999–2000, 2003–2004, and 2005–2006.
In addition, in a population-based cohort of
adolescents and young adults in Taiwan, Lin
et al. (2013) observed a positive association
between serum levels of PFNA and serum
levels of thyroxine (T
4
). Yet, other studies
have reported no association between PFOS
or PFOA levels and thyroid function. ese
include occupational studies with high levels
of exposure (Olsen et al. 2003; Olsen and
Zobel 2007); a study of residents of a water
district in south eastern Ohio, where there is
significant environmental exposure to PFOA
(Emmett 2006); studies of popula tions in
Korea (Ji et al. 2012) and China (Lin et al.
2013); a study of Inuit adults (Dallaire et al.
2009); and studies of pregnant women (Chan
et al. 2011; Inoue et al. 2004). In the United
States, one of the largest efforts to investigate
the impact of exposures to PFCs was initiated
by the C8 Science Panel, which was created
as part of a settlement agreement stemming
from PFOA (or C8) contamination of drink-
ing water in six water districts in two states
near the DuPont Washington Works facil-
ity near Parkersburg, West Virginia (Frisbee
et al. 2009). In this exposed popu la tion, high
environmental levels of PFOA in water were
associated with delayed onset of puberty in
girls (Lopez-Espinosa et al. 2011) as well as
earlier menopause (Knox et al. 2011). Knox
et al. (2011) found that serum PFOS and
PFOA were significantly higher (p < 0.0001)
in women 40–55 years of age who had a hys-
terectomy compared with women who had
not. However, because the authors did not
observe the timing of PFC exposure relative
to menopause, causal inference is limited.
One non causal explanation for an association
between PFCs and natural meno pause is that
elimination of PFCs via the loss of menstrual
blood and tissue might result in lower serum
levels in menstruating women than in post-
menopausal women (Knox et al. 2011).
We investigated associations between
multiple PFCs (PFOS, PFOA, PFNA, and
PFHxS) and age at natural and surgically
induced (hysterectomy) meno pause using
NHANES data. NHANES collected informa-
tion regarding the age at which women
experienced menopause, which allowed us
Address correspondence to K.W. Taylor, National
Toxicology Program, PO Box 12233, MD K2–04,
Research Triangle Park, NC 27709 USA. Telephone:
(919) 316-4707. E-mail: taylorkw@niehs.nih.gov
is article is the work product of employees of
the National Institute of Environmental Health
Sciences (NIEHS), National Institutes of Health
(NIH); however, the statements, opinions, or con-
clusions contained in the article do not necessarily
represent the statements, opinions, or conclusions of
the NIEHS, NIH, or the United States government.
e authors declare they have no actual or potential
competing financial interests.
Received: 25 February 2013; Accepted: 26 November
2013; Advance Publication: 26 November 2013; Final
Publication: 1 February 2014.
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to investigate the relationship between serum
levels and time since menopause and the
possibility of reverse causality.
Methods
Study population. NHANES is a nationally
representative, cross-sectional survey of about
5,000 persons each year, with survey partici-
pants located in counties across the United
States. The survey uses in-home interviews
and physical examinations in a mobile exami-
nation unit to collect data on demo graphics,
behavioral and environmental risk factors, and
health status [Centers for Disease Control and
Prevention (CDC) 2012]. Written consent
was obtained from all NHANES partici-
pants after approval by the NCHS (National
Center for Health Statistics) Research Ethics
Review Board (CDC 2012). Details regarding
interview, examina tion, and sample collec-
tion proto cols have been described previously
(CDC 2013a). Because the present study is
based on previously collected data that have
been deidentified, the University of North
Carolina Institutional Review Board deter-
mined the study to be exempt from review.
PFC measurement. The National Center
for Environmental Health analyzed individual
serum PFC levels in five NHANES sample
waves: 1999–2000, 2003–2004, 2005–2006,
2007–2008, and 2009–2010. In each wave,
a random one-third subset of partici pants
≥ 12 years of age was selected for assess ment
of 12 PFCs (CDC 2009). Detailed analytic
methods have been described previously
(Calafat et al. 2007a, 2007b; Kato et al. 2011).
Briefly, serum samples were analyzed using
automated solid-phase extraction coupled
to reverse-phase high-performance liquid
chromatography/tandem mass spectrometry.
The laboratory methods and comprehensive
quality control system were consistent across
each NHANES wave, and documenta-
tion for each wave is available online (CDC
2013b). We examined PFOS, PFOA, PFNA,
and PFHxS in relation to menopausal status
because these com pounds were detected in
> 95% of samples compared with other PFCs,
which were detected infrequently (Calafat et al.
2007a, 2007b; Kato et al. 2011). Any partici-
pant with a serum PFC concentration below
the limit of detection (LOD) was assigned a
serum level of the LOD divided by the square
root of 2 (Calafat et al. 2007a, 2007b; Kato
et al. 2011). Serum PFC concen tra tions were
categorized into tertiles based on distributions
among all women in the study sample. We
considered other categoriza tions, including
quartiles and quintiles, but results were similar
regardless of the categoriza tion used (results
not shown). We chose to catego rize by tertile
to increase the stability of our estimates.
Menopausal status. Women ≥ 18 years
of age completed a reproductive health
questionnaire. They were asked “Have you
had at least one menstrual period in the past
12 months? (Please do not include bleedings
caused by medical conditions, hormone ther-
apy, or surgeries.).” Women who answered
“no” were subsequently asked “What is the
reason that you have not had a period in the
past 12 months?” We classified women as
premenopausal if they answered “yes” to the
first question or answered “no” to the first
question but indicated the reason as preg-
nancy, breastfeeding, irregular periods, or
medical conditions/treatments (n = 1,800).
We classified women as post menopausal if
they answered “no” to the first question and
indicated the reason to be natural meno pause
(n = 501) or hysterectomy (n = 431). We
excluded from all analyses 265 women with
no information on their menopausal status
and 14 who answered that they had not had
their period in the last 12 months but did
not state why (Figure 1). e distribution of
demo graphic characteristics and PFC levels
among these women were similar to those
of the combined larger sample, except that
most women were missing data for parity. For
women who reported having gone through
menopause, age at occurrence was recorded.
We calculated time since menopause by sub-
tracting the age at which post menopausal
women reported having their last menstrual
period from their age at the time of survey.
Statistical analyses. We used proportional
hazard modeling to estimate hazard rate
[hazard ratios (HRs)] of the onset of natural
menopause as a function of age and serum
PFC levels. Premenopausal women were cen-
sored at their age at the time of the survey.
Analyses were performed in SAS (version 9.2;
SAS Institute Inc., Cary, NC) using the Proc
SURVEYPHREG procedure, which accounts
for stratification and clustering within primary
sampling units used to select the NHANES
sample. Rather than using NHANES sample
weights, we adjusted all models for covari-
ates related to the NHANES sample selection
procedure (age and race/ethnicity), a method
that balances the trade-off between efficiency
and bias (Graubard and Korn 1999; Korn and
Graubard 1991). To determine the robust-
ness of our results, we also conducted analy-
ses using the NHANES sample weights. e
inclusion of weights made no appreciable dif-
ference in the magnitude or precision of the
associations (results not shown); therefore, we
present the unweighted analyses.
Covariates. We considered a number
of covariates as possible confounders in the
association between PFCs and menopause.
We used information on the association
between other persistent organic pollutants and
menopause to develop a directed acyclic graph
(Weng et al. 2009) that inferred the following
confounders: age, race, parity, education,
and smoking (Figure 2) (Cooper et al. 2002;
Knox et al. 2011). We did not adjust for body
mass index (BMI; body weight in kilograms
divided by height in meters squared) for several
reasons. Steenland et al. (2009) reported
an association between serum PFC levels
and BMI, suggesting that BMI could be a
potential intermediate on the causal pathway
between PFC exposure and menopause.
High BMI has also been associated with
later onset of natural menopause (Akahoshi
2002). However, in a study using data from
NHANES, Nelson et al. (2010) found no
consistent association between serum PFC
Figure1. Study population of women 20–65years of age who had PFC serum measurements: NHANES
years 1999–2000, 2003–2004, 2005–2006, 2007–2008, and 2009–2010.
1999–2000
(n = 433)
2003–2004
(n = 526)
2005–2006
(n = 613)
2007–2008
(n = 665)
2009–2010
(n = 777)
All years
(n = 3,011)
Have you had at least one menstrual period in the past 12 months? (Please do
not include bleedings caused by medical conditions, hormone therapy, or surgeries.)
Yes, or no because of
pregnancy, breastfeeding, or
medical conditions/treatments
(n = 1,800)
What is the reason that you have not
had a period in the past 12 months?
Missing
(n = 265)
No
(n = 946)
Menopause
(n = 501)
Hysterectomy
(n = 431)
No response
(n = 14)
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levels and BMI; thus, BMI did not meet
criteria as a potential confounder (Greenland
and Robins 1986). Because BMI generally
increases after menopause, BMI reported at the
time of the survey may not reflect BMI at the
time of menopause. erefore, we examined
whether inclusion of BMI in our model would
appreciably alter the association between
PFCs and menopause (HR change > 10%)
and found that it did not (results not shown).
We also considered adjustment for NHANES
wave. However, because sample wave was
strongly associated with serum PFC levels but
not age at menopause, it was not included
as a covariate. Age at the time of interview
was modeled as a continuous variable. Race/
ethnicity, education, smoking, and parity were
modeled as categorical variables (Table 1).
Reverse causation. PFCs may be excreted
in blood and tissue during menstruation (Knox
et al. 2011); therefore, women who are no lon-
ger menstruating may have higher levels of
PFCs because they lack that elimination path-
way. Consequently, any association between
serum PFC levels and rate of natural meno-
pause may be the result of reverse causation.
We investigated the potential for reverse causa-
tion in two ways. First, we used proportional
hazard models to examine the association
between PFC levels and rate of hysterectomy.
Premenopausal women were censored at their
age at interview, and post menopausal women
were censored at the age of menopause. If we
assume that the reasons for hysterectomy are
not related to PFC exposure, an observed posi-
tive association between PFC levels and hyster-
ectomy suggests reverse causation. Conversely,
if there is no reverse causation, we would
expect to see no association between PFC level
and hysterectomy. Second, we investigated
whether the rate of natural menopause predicts
PFC levels; if the absence of menstrual blood
and tissue loss explains the association between
PFCs and self-reported natural menopause,
we would expect women who menstruated
more recently to have lower serum levels of
PFCs. We used generalized additive models
(GAMs) to examine the shape of the relation-
ship between years since natural menopause
and PFCs among post menopausal women
and determined that a linear approxi mation
appropriately represented the shape of the
relationship (results not shown). We report
results from linear regression models in SAS
Proc SURVEYREG. Statistical significance
was defined as p = 0.05.
Results
Among the 2,732 women with both PFC
measure ments and menstrual status data,
65.9% (n = 1,800) were pre menopausal,
18.3% (n = 501) had completed natural
menopause, and 15.7% (n = 431) had hys-
terectomies (Table 1). At the time of the
survey, pre menopausal women were generally
younger (median age, 34 years), and women
who had gone through natural menopause
were the oldest (median age, 58 years). The
median age at last period among women
who had completed natural menopause was
49 years. We detected PFOS, PFOA, PFHxS,
and PFNA in at least 95% of serum samples,
similar to previous reports from the larger
NHANES population (Calafat et al. 2007a,
2007b; Kato et al. 2009). e pre menopausal
group had the lowest median PFC levels,
Figure2. Directed acyclic graph of association between PFC exposure and age of natural menopause.
PFC
exposure
Age of natural
menopause
NHANES
cycle
BMI
Education
Smoking
Age
Parity
Table1. Demographic characteristics of women 20–65years of age who either had their period (pre-
menopausal), had experienced menopause, or had experienced hysterectomy: NHANES 1999–2000,
2003–2004, 2005–2006, 2007–2008, and 2009–2010.
a
Characteristic Premenopause Menopause Hysterectomy
Population (n) 1,800 501 431
Age at interview (years; median ± SD) 34 ± 9.61 58 ± 5.25 55 ± 8.46
Age at last period (years; median ± SD) 49 ± 4.67 38 ± 7.66
NHANES cycle
1999–2000 282 (15.67) 67 (13.37) 48 (11.14)
2003–2004 298 (16.56) 84 (16.77) 98 (22.74)
2005–2006 403 (22.39) 83 (16.57) 75 (17.40)
2007–2008 389 (21.61) 125 (24.95) 110 (25.52)
2009–2010 428 (23.78) 142 (28.34) 100 (23.20)
Race/ethnicity
White non-Hispanic 790 (43.89) 225 (44.91) 209 (48.49)
Black non-Hispanic 345 (19.17) 96 (19.16) 101 (23.43)
Mexican American 433 (24.06) 115 (22.95) 65 (15.08)
Other Hispanic 159 (8.83) 43 (8.58) 38 (8.82)
Other (including multi racial) 73 (4.06) 22 (4.39) 18 (4.18)
Education (years)
<12 440 (24.47) 158 (31.54) 112 (25.99)
12 359 (19.97) 100 (19.96) 127 (29.47)
>12 999 (55.56) 243 (48.50) 192 (44.55)
Missing 2 0 0
BMI (kg/m
2
)
Underweight (<18.5) 46 (2.56) 6 (1.21) 4 (0.94)
Normal weight (18.5 to <25) 569 (31.74) 129 (26.01) 72 (16.98)
Overweight (25 to <30) 516 (28.76) 140 (28.23) 123 (29.01)
Obese (>30) 663 (36.96) 221 (44.56) 225 (53.07)
Missing 6 5 7
Ever smoked
No 1,188 (66.00) 270 (53.89) 230 (53.36)
Yes 612 (34.00) 231 (46.11) 201 (46.64)
Missing 0 0 0
Parity (no. of live births)
0 388 (23.08) 62 (13.11) 39 (9.24)
1 339 (20.17) 66 (14.00) 60 (14.22)
>1 954 (56.75) 344 (72.89) 323 (76.54)
Missing 119 29 9
PFC exposure [ng/mL; median (T1, T3)]
PFOS 10.3 (6.0, 17.0) 14.03 (8.80, 23.9) 17.50 (10.6, 29.4)
PFOA 2.70 (1.80, 4.20) 3.80 (2.50, 5.30) 4.20 (2.90, 5.90)
PFNA 0.90 (0.60, 1.40) 1.20 (0.80, 1.80) 1.30 (0.80, 2.10)
PFHxS 1.00 (0.60, 1.80) 1.50 (0.90, 2.60) 1.70 (1.10, 3.10)
T, tertile. Values are n(%) except where indicated.
a
Women with unknown menopausal status were excluded.
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whereas the post hysterectomy group had the
highest median levels (Table 1). For women in
our study, serum collection and completion of
reproductive health questionnaires took place
a median of 7.5 years after natural menopause
[inter quartile range (IQR), 8 years] and a
median of 14 years after hysterectomy (IQR,
16.5 years). In addition, PFC measurements
were available for 265 women who lacked data
on menstrual status and for 14 who indicated
they had not had a period in the past year but
did not report the reason.
After adjusting for age at interview, race/
ethnicity, education, smoking status, and
parity, women with higher serum levels of
PFCs (tertiles 2 and 3) consistently had higher
rates of menopause than women in tertile 1
(Figure 3). ere appeared to be a monotonic
dose–response association of PFOA, PFNA,
and PFHxS with menopause. The adjusted
HRs for women with the highest serum
levels of PFOA, PFNA, and PFHxS (tertile 3
compared with tertile 1) were 1.36 (95% CI:
1.05, 1.75), 1.47 (95% CI: 1.14, 1.90), and
1.70 (95% CI: 1.36, 2.12), respectively. e
adjusted HRs for tertile 2 versus tertile 1 were
1.22 (95% CI: 0.92, 1.62) for PFOA, 1.43
(95% CI: 1.07, 1.91) for PFNA, and 1.42
(95% CI: 1.08, 1.87) for PFHxS. For serum
PFOS, adjusted HRs were higher in tertile 2
than in tertile 3.
We observed robust, positive dose–
response associations for all four PFCs and
hysterectomy (Figure 4). PFHxS was most
strongly associated with the rate of hysterec-
tomy (adjusted HR = 3.50; 95% CI: 2.72,
4.50) in tertile 3. Although the HRs for
PFOS and PFOA are lower than those for
PFHxS, the monotonic pattern of increasing
HRs for PFOS and PFOA appears fairly simi-
lar to that of PFHxS. Using linear regression
models, we found that levels of all four PFCs
increased with each additional year since
natu ral menopause (Table 2).
Discussion
Higher body burdens of PFCs were associ-
ated with earlier onset of natural menopause.
Associations were strongest between serum
levels of PFNA and PFHxS and the rate of
natural menopause. PFNA and PFHxS have
not been studied previously with respect to
menopause, which is of concern because
PFNA and PFHxS have not declined over
time in the same manner as PFOA and PFOS
(Andersen et al. 2008; Calafat et al. 2007b;
Kato et al. 2011); geometric mean serum lev-
els of PFNA are increasing (e.g., from 0.55
to 1.49 ng/mL between survey years 1999–
2000 and 2007–2008), and serum levels of
PFHxS increased in 2007–2008 compared
with previous years (Kato et al. 2011). Results
of the present study show positive associa-
tions between PFOS and PFOA and earlier
menopause, consistent with previous reports
in the literature (Knox et al. 2011). As we
anticipated, serum levels of PFOA were lower
in our sample (median, 3.8 ng/mL) com-
pared with the C8 Health Study (medians
of 17.6 ng/mL in women 18 to ≤ 42 years
of age and 23.4 ng/mL in women > 42 and
≤ 51 years of age) (Knox et al. 2011), which
had high levels of PFOA due to industrial
contamination. Despite lower levels, we
also observed a positive association between
PFOA and the rate of natural menopause.
Although we observed associations for all
PFCs assessed, we cannot rule out the pos-
sibility that associations are driven by a single
congener, because some PFCs in sera are cor-
related. Using NHANES data, Calafat et al.
(2007b) found statistically significant correla-
tions (p < 0.001) between the log-transformed
concentrations of PFOS and PFOA [Pearson
correlation coefficient (r) = 0.66], PFHxs
(r = 0.56), and PFNA (r = 0.50). e correla-
tion coefficient between the log-transformed
concentrations of PFOA and PFHxS was
Table2. Adjusted β (95% CI)
a
for the change in
serum PFC concentrations (ng/mL) associated
with a 1-year increase in the time between natu ral
menopause and sample collection among natu-
rally post menopausal women (n=501): NHANES
1999–2000, 2003–2004, 2005–2006, 2007–2008, and
2009–2010.
PFC β (95% CI)
a
PFOS 0.23 (–0.16, 0.48)
PFOA 0.07 (0.013, 0.13)
PFNA 0.02 (0.002, 0.042)
PFHxS 0.023 (–0.019, 0.065)
a
Adjusted for age at time of survey, race/ethnicity,
education, smoking, and parity.
Figure3. Adjusted (Adj) HRs and 95%CIs for menopause in association with tertiles (T) of serum PFCs
among women 20–65years of age: NHANES 1999–2000, 2003–2004, 2005, 2006, 2007–2008, and 2009–2010.
Data are based on the proportional hazards model for age at menopause, censoring at interview age if
still menstruating, and eliminating all cases of hysterectomy. HRs are adjusted for age at interview, race/
ethnicity, education, smoking, and parity.
15
HR
PFOS
T1 (0.14 to 9 ng/mL) 634 1
T2 (> 9 to 18.4 ng/mL) 756 1.23 (1.04, 1.44)
T3 (> 18.4 ng/mL) 761 1.16 (0.91, 1.48)
PFOA
T1 (0.07 to 2.5 ng/mL) 649 1
T2 (> 2.5 to 4.4 ng/mL) 723 1.22 (0.92, 1.62)
T3 (> 4.4 ng/mL) 779 1.36 (1.05, 1.75)
PFNA
T1 (0.07 to 0.80 ng/mL) 668 1
T2 (> 0.80 to 1.5 ng/mL) 712 1.43 (1.07, 1.91)
T3 (> 1.5 ng/mL) 771 1.47 (1.14, 1.90)
PFHxS
T1 (0.07 to 0.90 ng/mL) 621 1
T2 (> 0.90 to 1.8 ng/mL) 715 1.42 (1.08, 1.87)
T3 (> 1.8 ng/mL) 815 1.70 (1.36, 2.12)
Exposure n Adj HR (95% CI)
Figure4. Adjusted (Adj) HRs and 95%CIs for hysterectomy in association with tertiles(T) of serum PFCs
among women: 20–65years of age NHANES 1999–2000, 2003–2004, 2005, 2006, 2007–2008, and 2009–2010.
Data are based on the proportional hazards model for age at hysterectomy, censoring at interview age if still
menstruating, and eliminating all cases of menopause. HRs are adjusted for age at interview, race/ethnicity,
education, smoking, and parity.
15
HR
Exposure n Adj HR (95% CI)
PFOS
T1 (0.14 to 9 ng/mL) 660 1
T2 (> 9 to 18.4 ng/mL) 706 1.44 (1.12, 1.85)
T3 (> 18.4 ng/mL) 733 2.56 (1.90, 3.43)
PFOA
T1 (0.07 to 2.5 ng/mL) 658 1
T2 (> 2.5 to 4.4 ng/mL) 696 1.83 (1.31, 2.56)
T3 (> 4.4 ng/mL) 745 2.81 (2.12, 3.71)
PFNA
T1 (0.07 to 0.80 ng/mL) 652 1
T2 (> 0.80 to 1.5 ng/mL) 692 1.39 (1.08, 1.80)
T3 (> 1.5 ng/mL) 755 1.78 (1.33, 2.37)
PFHxS
T1 (0.07 to 0.90 ng/mL) 633 1
T2 (> 0.90 to 1.8 ng/mL) 683 2.22 (1.66, 2.98)
T3 (> 1.8 ng/mL) 783 3.50 (2.72, 4.50)
Page 4
PFCs and menopause among women from NHANES
Environmental Health Perspectives
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149
0.46; between PFOA and PFNA, r = 0.55.
In the present study, Spearman correlations
ranged from 0.19 between PFOS and PFNA
to 0.65 between PFOS and PFOA (p < 0.001
for all correlations). We considered the use
of a total (summed) exposure measure of all
four PFC congeners; however, serum levels of
PFOS were much higher than those of PFOA,
PFHxS, and PFNA, suggesting that the com-
bined analysis would dis proportionately reflect
PFOS levels.
Early menopause is associated with a num-
ber of adverse health impacts. For example,
results from a meta-analysis demonstrated that
menopause before 50 years of age was asso-
ciated with a 25% increased risk of cardio-
vascular disease (Atsma et al. 2006) and
menopause before age 46 has been associated
with increased risk of coronary heart disease
and stroke (Lisabeth et al. 2009; Wellons et al.
2012). If PFC levels are predictors of earlier
menopause, exposure may also be responsible
for increased risk of other serious health out-
comes (e.g., cardio vascular disease and stroke).
Our examination of reverse causality
indicated positive associations between all
four of the PFCs we examined and the rate
of hysterectomy, and showed that these
PFC levels increased with time since natural
menopause. Taken together, the results of
these two additional analyses suggest that the
association between PFCs and menopause
may reflect the accumulation of PFCs among
women who were not excreting them through
menstruation. However, because of the cross-
sectional natural of our data, we cannot
confirm the direction of these associations.
Prospective human studies evaluating the
onset of menopause are necessary to better
assess potential causality.
Using data from the large, U.S. representa-
tive NHANES sample allowed us to explore
the association between PFCs and the haz-
ard of natural menopause while adjusting for
potential confounding by a number of vari-
ables. Unlike previous analyses of PFCs and
natural menopause, NHANES collected infor-
mation on the time since natural menopause
and surgical hysterectomy, which allowed us
to address the potential for reverse causality.
e cross-sectional nature of data collection
does not allow us to establish temporality
because menopause status, age at menopause,
and PFC measurements were taken at the
same time. PFC measurements were based on
a single serum sample. Any misclassification
from single measures would tend to decrease
power and under estimate the real strengths
of association (Pearce et al. 2007). Although
a single sample may be more reliable for com-
pounds with long half-lives, samples collected
at several time points would be more accu-
rate for classifying exposure in future studies
(Melzer et al. 2010).
Conclusions
e consistency and robustness of our findings
suggest a relationship between PFCs and
menopause, although the under lying mecha-
nism of that association remains unknown.
In these cross-sectional data, it is not clear
whether the association observed between
PFCs and menopause is causal, if results are
due to non causal influences such as biases
from confounding or misclassification, or
if results are due to accumulation of PFCs
after menopause. Regardless of the under lying
cause, women appear to accumulate PFCs
more rapidly after they are no longer menstru-
ating. ese results, along with the ubiquitous
nature of exposure and persistence of PFCs in
the environment, support the need for contin-
ued monitoring of serum levels in the general
popu lation as well as further studies of the
reproductive health effects of PFCs.
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  • Source
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    Full-text · Article · Mar 2015 · Metabolomics
  • Source
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    Full-text · Article · Jan 2015 · PLoS ONE
  • Source
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