Relationship between urinary Bisphenol A (BPA) levels and diabetes mellitus

Relationship between Urinary Bisphenol A Levels and Diabetes Mellitus

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3232607/?report=printable

J Clin Endocrinol Metab. 2011 December; 96(12): 3822–3826.

PMCID: PMC3232607

Published online 2011 September 28. doi: 10.1210/jc.2011-1682

Anoop Shankar and Srinivas Teppala
Department of Community Medicine, West Virginia University School of Medicine, Morgantown, West Virginia 26506
Corresponding author.
Address all correspondence and requests for reprints to: Dr. Anoop Shankar, Department of Community Medicine, West Virginia University
School of Medicine, P.O. Box 9190, Morgantown, West Virginia 26506-9190. E-mail: ashankar@hsc.wvu.edu.
Received June 3, 2011; Accepted September 6, 2011.
Copyright © 2011 by The Endocrine Society

Abstract
Background:

Bisphenol A (BPA) is a widely used chemical in the manufacture of polycarbonate plastics and epoxy
resins. Recent animal studies have suggested that BPA exposure may have a role in the development
of weight gain, insulin resistance, pancreatic endocrine dysfunction, thyroid hormone disruption, and
several other mechanisms involved in the development of diabetes. However, few human studies have
examined the association between markers of BPA exposure and diabetes mellitus.
Methods:

We examined the association between urinary BPA levels and diabetes mellitus in the National
Health and Nutritional Examination Survey (NHANES) 2003–2008. Urinary BPA levels were
examined in quartiles. The main outcome of interest was diabetes mellitus defined according the
latest American Diabetes Association guidelines.
Results:

Overall, we observed a positive association between increasing levels of urinary BPA and diabetes
mellitus, independent of confounding factors such as age, gender, race/ethnicity, body mass index,
and serum cholesterol levels. Compared to quartile 1 (referent), the multivariate-adjusted odds ratio
(95% confidence interval) of diabetes associated with quartile 4 was 1.68 (1.22–2.30) (p-trend =
0.002). The association was present among normal-weight as well as overweight and obese subjects.
Conclusions:

Urinary BPA levels are found to be associated with diabetes mellitus independent of traditional
diabetes risk factors. Future prospective studies are needed to confirm or disprove this finding.

Bisphenol A (BPA) is a chemical produced in very high volume, with more than 2 million metric tons
produced worldwide in 2003 (1). It is used extensively in the manufacture of epoxy resins,
polycarbonate plastics, and food and beverage containers (1), and detectable levels of BPA in urine
have been shown to be present in the majority of U.S. adults (2, 3). BPA has been shown to have
estrogenic and thyroid hormone-disrupting effects (1, 4, 5). Recent evidence, especially from animal
studies, suggests that BPA exposure may have a role in weight gain, development of obesity and
insulin resistance, and the subsequent development of diabetes mellitus (6, 7). However, the
association between BPA levels and diabetes mellitus in humans is not clear.
Two previous studies (8, 9) have examined the association between urinary BPA levels and diabetes

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and reported opposing findings—with one study reporting a positive association (8) and the other not
detecting an association (9). However, both of the studies (8, 9) used self-reported diabetes as the
outcome; fasting glucose or glycosylated hemoglobin was not used as a criterion in defining diabetes
in these studies as recommended by recent guidelines (10). Studies (11) have shown that, when using
self-reported diabetes as opposed to blood glucose measurements, there is likely to be substantial
misclassification of diabetes status and this may consequently lead to biased risk associations. In this
context, we examined the association between urinary BPA levels and diabetes mellitus in the 2003 to
2008 National Health and Nutritional Examination Survey (NHANES), a representative sample of
U.S. adults. In the current report we had fasting glucose levels as well as glycosylated hemoglobin to
define diabetes mellitus according to the latest American Diabetes Association guidelines.

Subjects and Methods
The current study is based on data from the NHANES 2003–2008. Detailed descriptions of NHANES
study design and methods are available elsewhere (12–14). In brief, the NHANES survey included a
stratified multistage probability sample representative of the civilian noninstitutionalized U.S.
population. Selection was based on counties, blocks, households, and individuals within households
and included the oversampling of non-Hispanic blacks and Mexican-Americans to provide stable
estimates of these groups. Subjects were required to sign a consent form before their participation,
and approval was obtained from the Human Subjects Committee of the U.S. Department of Health
and Human Services.
The current study sample consisted of participants more than 20 yr old among whom urinary BPA
was available (n = 4792). We excluded subjects with self-reported cardiovascular disease (n = 495)
and also subjects with missing data (n = 330) on covariates included in the multivariable model,
including level of education, smoking status, serum or fasting glucose levels, systolic or diastolic blood
pressure, body mass index (BMI), or cholesterol levels. This resulted in 3967 participants (51.7%
women), 467 of whom had diabetes.
Exposure measurements

Age, gender, race/ethnicity, smoking status, alcohol intake (grams per day), level of education, history
of diabetes, and oral hypoglycemic intake or insulin administration were assessed using a
questionnaire (12–14). Individuals who had not smoked more than 100 cigarettes in their lifetime
were considered never smokers; those who had smoked more than 100 cigarettes in their lifetime were
considered former smokers if they answered negatively to the question “Do you smoke now?” and
current smokers if they answered affirmatively. BMI was calculated as weight in kilograms divided by
height in meters squared.
Rigorous procedures with quality control checks were used in blood collection, and details about these
procedures are provided in the NHANES Laboratory/Medical Technologists Procedures Manual
(12–14). Seated systolic and diastolic blood pressures were measured using a mercury
sphygmomanometer according to the American Heart Association and Seventh Joint National
Committee recommendations (15). Up to three measurements were averaged for systolic and diastolic
blood pressures. Patients were considered hypertensive if they reported the current use of blood
pressure-reducing medication and/or had systolic blood pressure greater than 140 mm Hg and/or
diastolic blood pressure greater than 90 mm Hg (15). Urinary creatinine was analyzed using the Jaffe
rate reaction method and using the CX3 analyzer (Beckman Coulter, Inc., Brea, CA) (16).
Previous measures of BPA in biological matrixes involved techniques such as gas chromatography
(GC) or HPLC (17). To achieve enhanced sensitivity and selectivity over previous methods, in the
current NHANES, measures of environmental phenols were derivatized to alkyl or acyl derivatives
before GC/mass spectrometry analysis (16). Using solid-phase extraction coupled to HPLC and
tandem mass spectrometry, detection levels of 0.1–2 ng/ml in 100 µl of urine were achieved, sufficient
for measuring urinary BPA levels in non-occupationally exposed participants (16).
Main outcome of interest: diabetes

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Serum glucose was measured using the modified hexokinase method at the University of Missouri
Diabetes Diagnostic Laboratory. Diabetes mellitus was defined based on the recent guidelines of the
American Diabetes Association (10) as a serum glucose greater than 126 mg/dl after fasting for a
minimum of 8 h, a serum glucose greater than 200 mg/dl for those who fasted less than 8 h before
their NHANES visit, a glycosylated hemoglobin value greater than 6.5%, or self-reported current use
of oral hypoglycemic medication or insulin.
Statistical analysis

Urinary BPA was categorized into quartiles (<1.10, 1.10–2.10, 2.11–4.20, and >4.20 ng/ml). We
hypothesized that high BPA levels are associated with diabetes mellitus. The odds ratio (OR) [95%
confidence interval (CI)] of diabetes for BPA was calculated by taking the lowest quartile (quartile 1)
as the referent and using multivariable logistic regression models. We used two models: the age- and
sex-adjusted model and the multivariable model, additionally adjusting for race/ethnicity
(non-Hispanic whites, non-Hispanic blacks, Mexican-Americans, and others), education categories
(below high school, high school, above high school), smoking (never smoker, former smoker, current
smoker), alcohol intake (nondrinker, moderate drinker, heavy drinker), BMI (normal, overweight,
obese), systolic blood pressure, diastolic blood pressure, urinary creatinine (milligrams per deciliter),
and total serum cholesterol (milligrams per deciliter). Trends in the OR of diabetes across increasing
urinary BPA categories were determined by modeling BPA as an ordinal variable. Sample weights that
account for the unequal probabilities of selection, oversampling, and nonresponse were applied for all
analyses using SAS (version 9.2; SAS Institute, Cary, NC) and SUDAAN software; SE values were
estimated using the Taylor series linearization method.

Results
Table 1 shows the baseline characteristics of the population by gender. Smokers were found to have a
statistically nonsignificant higher mean BPA level (4.17 ± 0.29 ng/dl) when compared with
nonsmokers (3.86 ± 0.19 ng/dl) (P = 0.216). Table 2 shows the association between increasing levels
of BPA and diabetes mellitus. Overall, we observed positive association between increasing BPA levels
and diabetes in both the age- and sex-adjusted model and the multivariable-adjusted model. Models
evaluating trend in this association were also statistically significant.
Table 3 shows the association between increasing BPA levels and diabetes mellitus by BMI categories.
We found that the association between increasing BPA levels and diabetes was consistently present
among normal-weight as well as overweight/obese subjects; p-trends for the association were also
significant. In a supplementary analysis, we examined the association between BPA and diabetes
separately among smokers and nonsmokers. We found that, consistent with our main findings in
Table 2, there was a positive association between BPA and diabetes among smokers and nonsmokers;
the p-interaction for the cross-product BPA × smoking status term was 0.6530, suggesting that the
association between BPA and diabetes did not differ by smoking status.

Discussion
In a large multiethnic, nationally representative sample, we found that increasing serum BPA levels
are positively associated with diabetes mellitus. The observed association was found to be
independent of confounding factors such as BMI, urinary creatinine (18), alcohol intake, and serum
cholesterol level. Our study adds to the emerging evidence of the role of environmental exposure to
BPA on cardiometabolic health in humans.
BPA is an environmental chemical used as a constituent monomer in polycarbonate plastics, which
are used extensively in drink containers and food packaging and in the production of oxidant used in
the lining of canned goods (1). Exposure to BPA is believed to be mainly through dietary intake, with
additional exposure through water, dental sealants, inhalation of household dusts, and exposure
through skin (1). Recent studies have documented that over 90% of the U.S. general population has
measurable concentrations of BPA metabolites in urine (2, 3).
Several lines of recent evidence suggest that an association between urinary BPA levels and diabetes
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mellitus may be biologically plausible. Animal studies have shown that BPA exposure may have a role
in weight gain and obesity development through several mechanisms, including the action of BPA on
preadipocytes (19, 20), a role as an estrogen (6), potential interactions with estrogen-related receptor
γ (21), action as a thyroid hormone antagonist (4), role as a peroxisome proliferator-activated receptor
γ antagonist (22), and its role in influencing pancreatic endocrine function (23). Furthermore,
Alonso-Magdalena et al. (24) in a recent experiment showed that mice exposed to BPA levels as low
as 10 µg/kg·d developed hyperinsulinemia, insulin resistance, and glucose intolerance. Finally,
Carwile and Michels (25) showed that urinary BPA levels are associated with obesity in the NHANES
survey. Therefore, it is possible that BPA may contribute to obesity and thereby indirectly to the
development of type 2 diabetes.
However, there are few studies in humans for comparison. Two previous studies (8, 9) have examined
the association between higher BPA levels and self-reported diabetes and have reported conflicting
results; whereas one study found a positive association (8), the other did not (9). However, it is well
known that in epidemiological studies (11), self-reported diabetes largely underdiagnoses the actual
prevalence of diabetes in a population. When using self-reported diabetes, a substantial number of
people who actually have diabetes may be misclassified as normoglycemic, and such a
misclassification would likely underestimate a true association if it is present. The main advantage of
our study over the previous two studies is that we defined diabetes consistent with the latest American
Diabetes Association guidelines (10) and included fasting glucose, nonfasting glucose, and
glycosylated hemoglobin levels in addition to self-reported diabetes. Consequently, we found that
there was a positive association between serum BPA levels and diabetes mellitus in this nationally
representative sample of U.S. adults. In subsequent stratified analysis, the observed association was
found to be present among both normal-weight and overweight/obese adults.
The main strengths of our study include its nationally representative sample, use of rigorous study
methods to collect the data, and the availability of extensive data on confounders. The main study
limitation is that the current study is cross-sectional in nature, therefore making it impossible to draw
cause and effect in the observed associations. Future prospective studies are required to confirm or
disprove our findings.
In summary, we found that in a nationally representative sample of U.S. adults, higher BPA levels
were positively associated with diabetes mellitus independent of confounding factors such as age,
BMI, alcohol intake, and cholesterol levels. If confirmed in future prospective studies, reducing
environmental exposure to BPA may have a role in the prevention of diabetes mellitus.

Acknowledgments
This study was funded by an American Heart Association National Clinical Research Program grant
(to A.S.) and National Institutes of Health Grant 5R03ES018888-02 (to A.S.).
Both authors contributed to the intellectual development of this paper. A.S. had the original idea for
the study, wrote the paper, and is the guarantor. S.T. performed the statistical analyses and was
involved in critical revisions to the manuscript.
Disclosure Summary: There are no conflicts of interest related to this manuscript.

Footnotes
Abbreviations:
BMI Body mass index
BPA bisphenol A
CI confidence interval
GC gas chromatography
OR odds ratio.

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Figures and Tables

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Table 1.

Baseline characteristics of the study population by gender
Characteristics

Men

Women

1879

2088

44.3 ± 0.5

45.6 ± 0.4

Non-Hispanic whites

953 (71.5)

991 (70.0)

Non-Hispanic blacks

373 (9.7)

425 (11.5)

Mexican-Americans

351 (8.5)

436 (8.0)

202 (10.2)

236 (10.4)

Below high school

511 (17.9)

560 (16.7)

High school

476 (25.5)

510 (24.9)

Above high school

892 (56.6)

1018 (58.4)

Never smoker

840 (45.7)

1289 (58.7)

Former smoker

529 (27.2)

403 (20.3)

Current smoker

510 (27.1)

396 (21.0)

Nondrinker

533 (24.5)

894 (35.7)

Moderate drinker

663 (38.7)

863 (47.3)

Heavy drinker

683 (36.8)

331 (17.0)

Normal weight (<25)

544 (28.6)

695 (40.3)

Overweight (25–30)

726 (38.1)

618 (26.5)

Obese (BMI ≥ 30)

609 (33.3)

775 (33.2)

Systolic blood pressure (mm Hg)

123.1 ± 0.4

119.1 ± 0.5

Diastolic blood pressure (mm Hg)

72.4 ± 0.4

69.2 ± 0.3

n
Age (yr)
Race/ethnicity

Others
Education categories

Smoking

Alcohol intake

BMI (kg/m2)

Urinary creatinine (mg/dl)

147.38 ± 2.63 106.55 ± 2.14

Total cholesterol (mg/dl)

201.55 ± 1.12 202.23 ± 1.03

Urinary BPA (ng/ml)
Diabetes (%)

3.97 ± 0.21

3.90 ± 0.26

229 (9.5)

238 (8.7)

Data are presented as weighted number (percentage) or mean ± SE by gender, as appropriate for the
variable.

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Table 2.

Association between urinary BPA and diabetes mellitus
BPA quartiles
(ng/ml)

Sample size (diabetes Age-, sex-adjusted, OR (95% Multivariable-adjusted, OR (95%
a
%)
CI)
CI)

Quartile 1 (<1.10)

1121 (8.3)

1 (referent)

1 (referent)

Quartile 2 (1.10–2.10)

905 (10.8)

1.55 (1.19–2.02)

1.42 (1.03–1.96)

Quartile 3 (2.11–4.20)

977 (11.2)

1.60 (1.25–2.05)

1.48 (1.05–2.08)

Quartile 4 (>4.20)

964 (12.8)

1.81 (1.36–2.43)

1.68 (1.22–2.30)

<0.0001

0.002

p-trend
a Adjusted for age

(years), gender, race-ethnicity (non-Hispanic whites, non-Hispanic blacks,
Mexican-Americans, others), education categories (below high school, high school, above high
school), smoking (never, former, current), alcohol intake (never, former, current), BMI (normal,
overweight, obese), systolic and diastolic blood pressure (mm Hg), urinary creatinine (mg/dl), and
total cholesterol (mg/dl).

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Table 3.

Association between urinary BPA and diabetes mellitus by BMI
Normal weight
BPA quartiles

Sample

(ng/ml)

Overweight/obese
Sample

size

Multivariable-adjusted, OR
a
(95% CI)

size

Multivariable-adjusted, OR
a
(95% CI)

Quartile 1 (<1.10)

408

1 (referent)

713

1 (referent)

Quartile 2

276

2.75 (1.03–7.33)

629

1.27 (0.90–1.79)

272

2.14 (0.79–5.81)

705

1.41 (1.00–1.98)

283

3.17 (1.23–8.18)

681

1.56 (1.09–2.24)

(1.10–2.10)
Quartile 3
(2.11–4.20)
Quartile 4 (>4.20)
p-trend

0.03

0.01

a

Adjusted for age (years), gender, race-ethnicity (non-Hispanic whites, non-Hispanic blacks,
Mexican-Americans, others), education categories (below high school, high school, above high
school), smoking (never, former, current), alcohol intake (never, former, current), systolic and
diastolic blood pressure (mm Hg), urinary creatinine (mg/dl), and total cholesterol (mg/dl).
Articles from The Journal of Clinical Endocrinology and Metabolism are provided here courtesy of The Endocrine Society

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Relationship between urinary Bisphenol A (BPA) levels and diabetes mellitus

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