Blueberries exert antihypertensive and vascular-protective effects in postmenopausal women with pre- and stage 1-hypertension

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RESEARCH
Original Research
Daily Blueberry Consumption Improves
Blood Pressure and Arterial Stiffness in
Postmenopausal Women with Pre- and Stage
1-Hypertension: A Randomized, Double-Blind,
Placebo-Controlled Clinical Trial
Sarah A. Johnson, PhD, RD, CSO; Arturo Figueroa, MD, PhD, FACSM; Negin Navaei; Alexei Wong, PhD; Roy Kalfon, MS;
Lauren T. Ormsbee, MS; Rafaela G. Feresin, MS; Marcus L. Elam, MS; Shirin Hooshmand, PhD; Mark E. Payton, PhD;
Bahram H. Arjmandi, PhD, RD
ARTICLE INFORMATION
Article history:
Accepted 27 October 2014
Available online 8 January 2015
Keywords:
Blueberries
Flavonoids
Nitric oxide
Pulse wave velocity
Vasodilation
Supplementary materials:
Podcast available at www.andjrnl.org/content/
podcast
2212-2672/Copyright ª2015 by the Academy of
Nutrition and Dietetics.
http://dx.doi.org/10.1016/j.jand.2014.11.001
ABSTRACT
Background Postmenopausal women have a high prevalence of hypertension and
often develop arterial stiffness thereby increasing cardiovascular disease risk. Although
antihypertensive drug therapies exist, increasing numbers of people prefer natural
therapies. In vivo studies and a limited number of clinical studies have demonstrated
the antihypertensive and vascular-protective effects of blueberries.
Objective To examine the effects of daily blueberry consumption for 8 weeks on
blood pressure and arterial stiffness in postmenopausal women with pre- and stage 1-
hypertension.
Design This was an 8-week, randomized, double-blind, placebo-controlled clinical trial.
Participants/setting Forty-eight postmenopausal women with pre- and stage 1-
hypertension recruited from the greater Tallahassee, FL, area participated.
Intervention Participants were randomly assigned to receive either 22 g freeze-dried
blueberry powder or 22 g control powder.
Main outcome measures Resting brachial systolic and diastolic blood pressures were
evaluated and arterial stiffness was assessed using carotid-femoral pulse wave velocity
and brachial-ankle pulse wave velocity. C-reactive protein, nitric oxide, and superoxide
dismutase were measured at baseline, 4 weeks, and 8 weeks.
Statistical analyses performed Statistical analysis was performed using a split plot
model of repeated measures analysis of variance.
Results After 8 weeks, systolic blood pressure and diastolic blood pressure (13117
mm Hg [P<0.05] and 759mmHg[P<0.01], respectively) and brachial-ankle pulse
wave velocity (1,401122 cm/second; P<0.01) were significantly lower than baseline
levels (13814 mm Hg, 807 mm Hg, and 1,498179 cm/second, respectively), with
significant (P<0.05) grouptime interactions in the blueberry powder group, whereas
there were no changes in the group receiving the control powder. Nitric oxide levels
were greater (15.3511.16
m
mol/L; P<0.01) in the blueberry powder group at 8 weeks
compared with baseline values (9.117.95
m
mol/L), whereas there were no changes in
the control group.
Conclusions Daily blueberry consumption may reduce blood pressure and arterial
stiffness, which may be due, in part, to increased nitric oxide production.
J Acad Nutr Diet. 2015;115:369-377.
HYPERTENSION IS A KNOWN MAJOR, YET
preventable, risk factor for the development of
cardiovascular disease (CVD), the leading cause of
death in the United States. According to the
American Heart Association, in the United States approxi-
mately 77.9 million, or one in three adults, have hyperten-
sion.
1,2
Although the prevalence of hypertension is associated
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ª2015 by the Academy of Nutrition and Dietetics. JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS 369

with aging in both sexes, the increased incidence of high
blood pressure, particularly systolic blood pressure (SBP), in
women after menopause exceeds that of men.
3,4
Endothelial
dysfunction has been suggested to play an important role in
the increases in blood pressure that occur after menopause.
Endothelial dysfunction is defined as changes in both
vascular tone and in endothelium-derived substances that in-
fluence vasodilation, such as a reduction in nitric oxide pro-
duction and bioavailability,
5
and vasoconstriction,
6,7
such as
an increase in the production of endothelin-1,
8
angiotensin
II,
9
and reactive oxygen species (ROS).
10,11
For instance, the
self-perpetuating cycle between oxidative stress and inflam-
mation that often occurs in a postmenopausal and/or a
hypertensive state leads to the upregulation of the enzyme
nicotinamide adenine dinucleotide phosphate-oxidase
(NADPH), which increases the production of ROS such as
superoxide anions in the arteries and the kidneys. These
ROS are then able to react with nitric oxide to form peroxyni-
trate leading to a reduction in nitric oxide bioavailability and
subsequently impaired nitric oxide-dependent vasodilation
that can result in hypertension.
12,13
In addition, endothelial
dysfunction is known to increase arterial stiffness, which is
involved in the development and progression of both hyper-
tension and CVD.
14,15
Therefore, endothelial function and
arterial stiffness should be targeted in the prevention and
treatment of hypertension.
The recommended intervention for controlling blood pres-
sure in pre- and stage 1-hypertension is not pharmaceutical
interventions but rather lifestyle modifications, including di-
etary approaches,
16
and there is evidence that many cases of
hypertension can be prevented and treated through diet
and lifestyle changes.
17,18
Considering the prevalence of hy-
pertension in the United States,
19
preventive strategies such as
dietary modifications (eg, functional foods and dietary sup-
plements) that aim to improve hypertension and its related
complications are warranted.
20
Epidemiologic evidence sug-
gests that dietary intake of certain flavonoids is associated
with a reduced risk of CVD risk factors, including hyperten-
sion.
21
In fact, Cassidy and colleagues
22
reported an 8%
reduction in the risk of hypertension in individuals in the
highest quintile of anthocyanin intake (primarily from blue-
berries and strawberries) compared with those in the lowest
quintile (relative risk 0.92; 95% CI 0.86 to 0.98; P<0.03).
Berries, including blueberries, and their polyphenols have
been reported
23
to improve several surrogate markers of car-
diovascular risk, including blood pressure, endothelial func-
tion, and arterial stiffness. Among all fruits, blueberries are one
of the richest sources of phenolic compounds, including fla-
vonoids, phenolic acids, and stilbenes,
24-26
which are known
to have biological activity and high antioxidant capacity
24,27,28
and they are a promising functional food with respect to
vascular health. For instance, Basu and colleagues
29
reported
that the consumption of 50 g freeze-dried highbush blue-
berries significantly lowered blood pressure in obese men and
women with metabolic syndrome after 8 weeks. The vascular-
improving effects of blueberries has been, in part, attributed to
the ability of its circulating polyphenol metabolites to inhibit
NADPH oxidase, which will enhance nitric oxide bioavailability
leading to enhanced endothelial-dependent vasodilation.
30
Despite the existence of the aforementioned studies,
there is a paucity of clinical studies investigating the
antihypertensive and vascular-protective effects of blue-
berries, particularly in postmenopausal women with pre-
and stage 1-hypertension. In addition, to our knowledge,
there are presently no studies that have investigated the
effects of blueberry consumption on arterial stiffness as
measured by pulse wave velocity, which is considered the
gold standard marker of arterial damage and is predictive of
CVD risk.
31
Therefore, the objective of this study was to bring
forth evidence that blueberry consumption would reduce
blood pressure and cardiovascular risk factors, including
endothelial dysfunction and arterial stiffness, in post-
menopausal women with pre- and stage 1-hypertension.
This randomized, double-blind, placebo-controlled clinical
trial tested the hypothesis that daily blueberry consumption
for 8 weeks would reduce arterial stiffening and improve
endothelial function resulting in reduced blood pressure.
SUBJECTS AND METHODS
Subjects
A total of 81 healthy, postmenopausal women aged 45 to 65
years with pre- and stage 1-hypertension (seated blood pres-
sure 125/85 mm Hg but 160/90 mm Hg at the screening
visit) were recruited from Tallahassee, FL, and surrounding
areas. Recruitment began in January 2012 and continued
through March 2013 when the final patient finished the study.
Those with diagnosed CVD; uncontrolled hypertension (>160/
100 mm Hg); receiving hormone replacement therapy or in-
sulin; active cancer, asthma, glaucoma, thyroid, kidney, liver,
and pancreatic disease; and heavy smokers (>20 cigarettes/
day) were excluded from the study. The Florida State Univer-
sity Institutional Review Board approved the study protocol
and all participants provided written informed consent. This
trial was registered at ClinicalTrials.gov: NCT01686282. After
an initial prescreening over the telephone, qualified partici-
pants were invited to the study site for their first visit. During
the first visit, written informed consent was obtained from all
participants by the study coordinator. Brachial blood pressure
measurements were taken in duplicate after 10 minutes
of seated rest with an automatic device (Omron Healthcare,
Inc). A complete medical and nutrition history was obtained
from participants by a registered dietitian nutritionist for
screening purposes. Based on inclusion and exclusion criteria,
a total of 48 postmenopausal women qualified and partici-
pated in the study. Participants were asked to maintain their
usual diet and physical activity pattern throughout the dura-
tion of the study.
Study Design and Intervention
Forty-eight postmenopausal women that met all inclusion
criteria were recruited to participate in an 8-week, random-
ized, double-blind, placebo-controlled clinical trial. Using a
statistician-pregenerated randomization list, eligible partici-
pants were randomly assigned by the study coordinator
to one of the two intervention groups: 22 g freeze-dried
blueberry powder or 22 g macronutrient-matched control
powder. The rationale for choosing this dose is that 22 g
freeze-dried blueberry powder equates to 1 cup fresh blue-
berries, which is feasible for people to consume on a
daily basis (Table 1). The blueberry powder consisted of
highbush freeze-dried blueberries (50/50 blend of tifblue
[Vaccinium virgatum] and rubel [Vaccinium corymbosum]) and
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370 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS March 2015 Volume 115 Number 3

the placebo powder consisted of maltodextrin, fructose,
artificial and natural blueberry flavoring, artificial purple and
red color, citric acid, and silica dioxide. The nutritional
composition of the freeze-dried blueberry powder and pla-
cebo powder was determined by Medallion Laboratories
(Table 1). The participants were asked to consume half of the
daily regimen (11 g) mixed with 1 cup (240 mL) water in the
morning and the second half mixed with 1 cup (240 mL)
water in the evening at least 6 to 8 hours apart. Participants
were encouraged to add vanilla extract and/or Splenda to the
regimen for added flavor based on their preference. The
freeze-dried blueberry powder and placebo powder regi-
mens used in this study were provided by the US Highbush
Blueberry Council and were distributed to subjects on a
biweekly basis. To monitor compliance, participants were
given customized calendars and were asked to record the
days they missed consuming the study regimen and return
any unused portion for compliance monitoring purposes.
Compliance was defined as missing 2 doses per week.
Anthropometric Assessments
Height without shoes was measured using a wall-mounted
stadiometer to the nearest 0.5 cm and weight was assessed
using a digital scale (Seca Corporation) to the nearest 0.1 kg.
Body mass index (BMI) was calculated as weight in kilo-
grams/height in meters
2
. Midabdominal waist circumference
was measured using a Gulick fiberglass measuring tape with
a tension handle (Creative Health Products, Inc). With the
exception of height measured at baseline, body weight and
waist circumference were repeatedly measured at baseline, 4
weeks, and 8 weeks.
Blood Collection and Analysis
Fasting venous blood for plasma and serum was collected
between 8:00 AM and 10:00 AM on a designated date from
each participant in vacutainers with appropriate anticoagu-
lants at baseline, 4 weeks, and 8 weeks. Serum and plasma
were separated by centrifuging at 4,000 rpm for 15 minutes
at 4C within 2 hours of collection using an IEC CL31R
multispeed centrifuge (Thermo Electron Corporation). Sam-
ples were then aliquoted and stored at e80C until analyses.
Serum levels of superoxide dismutase (SOD) and plasma
levels of nitric oxide and C-reactive protein were measured in
duplicate at baseline, 4 weeks, and 8 weeks using the
following commercially available kits: Superoxide Dismutase
Assay Kit, Nitrate/Nitrite Colorimetric Assay Kit, and C-Reac-
tive Protein (human) EIA Kit according to the manufacturer’s
(Cayman Chemicals) instructions.
Blood Pressure and Arterial Function
Cardiovascular measurements were performed at baseline, 4
weeks, and 8 weeks on the same day as blood collection and
in the supine position in a quiet, temperature-controlled
room (23C1C) after an overnight fast and avoidance of
alcohol and caffeine for at least 24 hours. Brachial blood
pressure, mean arterial pressure, carotid-femoral pulse wave
velocity (cfPWV), and brachial-ankle pulse wave velocity
(baPWV) were measured using an automatic device (VP-
2000; Omron Healthcare). Appropriate-size blood pressure
cuffs were wrapped around both arms (brachial artery) and
ankles (posterior tibial artery). Electrocardiogram electrodes
were placed on the forearms, and a heart sound microphone
was placed on the chest. Participants rested for at least 20
minutes before data collection. Transit time was automati-
cally determined from the time delay between the feet of the
pulse waves related to the R-wave of the electrocardiogram.
The distance from the carotid and femoral artery was
measured with a nonelastic tape measure as a straight line,
whereas the distance from the brachial to tibial arteries was
calculated automatically according to the participant’s
height.
32
Pulse wave velocity was calculated as distance
divided by transit time.
32
Two measurements were collected
and averaged at each time point. Heart rate was determined
from the electrocardiogram.
Statistical Analyses
An initial sample size of 24 participants per group with an
attrition rate of 17% was able to produce a sample size of
approximately 20 participants with >80% power to detect a
significant difference (P<0.05). The sample size was calcu-
lated using a study conducted by Basu and colleagues,
29
which indicated that an intake of 50 g freeze-dried blue-
berry powder was effective in lowering SBP and diastolic
blood pressure (DBP) (e6% and e4%, respectively) compared
with controls (e1.5% and e1.2%).
Statistical analysis was performed using analysis of vari-
ance methods with PROC MIXED in PC SAS (version 9.1,
2006, SAS Institute). Descriptive statistics were calculated
for all variables including means, standard deviations,
Table 1. Nutrient composition of freeze-dried blueberry
and placebo powders compared with fresh blueberries
Placebo
powder
(per 22 g)
a
Freeze-dried
blueberry
powder
(per 22 g)
a
Fresh
blueberry
(per c)
b
Energy (kcal) 86 87 83
Fat (g) 0.02 0.26 0.48
Total
carbohydrates (g)
20.82 20.57 21.02
Fiber (g) 0 4.73 3.50
Protein (g) 0.17 0.59 1.08
Vitamin C (mg) 0 2.27 14.10
Calcium (mg) 0 7.50 9.00
Potassium (mg) 0 103.18 112
Oxygen radical
absorbance
capacity
(
m
mol TE
c
)
0 8,052 Unknown
Phenolics (mg) 0 844.58 Unknown
Anthocyanins (mg) 0 469.48 Unknown
a
Analyzed by Medallion Laboratories.
b
US Department of Agriculture National Nutrient Database for Standard Reference.
c
TE¼Trolox equivalents.
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March 2015 Volume 115 Number 3 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS 371

medians, minima, and maxima. Distributions of outcome
variables were examined graphically for asymmetry and
for outliers. When a lack of symmetry was noted, the vari-
able was transformed before analysis. Baseline values of
serum, anthropometric, and dietary variables, which
were normally distributed between the two experimental
groups, were compared using two-sample ttests. The main
and interaction effects of the intervention (freeze-dried
blueberry powder or placebo) and time (baseline, 4 weeks,
and 8 weeks) on primary outcome variables (blood pres-
sure) and secondary outcome variables (pulse wave velocity
and blood biomarkers) were evaluated. A split plot model of
two (group)three (time) repeated measures analysis of
variance was used for statistical analysis both within and
between treatment groups. The mean changes in outcome
variables during the intervention periods were compared by
analyzing interaction effects of intervention and time, using
the SLICE option (to analyze simple effects) in a least square
means statement. Data are reported as least square mean-
standard deviation. In all statistical comparisons, differ-
ences with P<0.05 were considered significant. Differences
with P<0.01 were noted.
RESULTS
Baseline Characteristics and Anthropometric
Measurements
Aflowchart of the study enrollment is presented in the
Figure. A total of 48 women who met the inclusion and
exclusion criteria were randomly assigned to receive either
22 g freeze-dried blueberry powder (25 participants) or 22 g
placebo powder (23 participants) daily for 8 weeks. The
overall attrition rate for the 8-week intervention study was
17% (20% for the treatment group and 13% for the control
group). Common reasons for not finishing the study included
noncompliance with the study protocol, claims of medical
and health-related issues such as gastrointestinal complaints,
and personal reasons such as lack of time (see the Figure).
Reported challenges to intake of the treatment regimens
included difficulty mixing powders with water, taste prefer-
ences, volume, and taste fatigue. The 40 participants who
completed the study were compliant with their treatments as
indicated in their daily dosing diaries.
Baseline characteristic data for participants who completed
the study are presented in Table 2. There were no statistically
significant differences between groups for baseline charac-
teristics including age, height, weight, BMI, and waist
circumference. The mean body weights, BMI, and waist cir-
cumferences for baseline, 4 weeks, and 8 weeks are pre-
sented in Table 2. There were no significant changes in either
group at any time point.
Blood Pressure and Arterial Stiffness
No significant differences were noted between groups at
baseline (Table 3). As presented in Table 3, after 8 weeks of
treatment, both SBP and DBP were significantly lower
(P<0.05 and P<0.01, respectively) than baseline levels
whereas there were no significant changes in the control
group. Significant (P<0.05) grouptime changes were noted
for both SBP and DBP at 8 weeks. In addition, in terms of
mean percent changes, there were 5.1% (range¼0% to e9.9%)
and 6.3% (range¼e1.3% to e11.0%) reductions in mean SBP
and DBP, respectively, in the blueberry group, whereas there
were no reductions in mean SBP (mean¼þ0.7%;
range¼e4.9% to þ6.7%) and DBP in the control group
(mean¼þ2.6%; range¼e2.5% to þ7.9%) There were no dif-
ferences observed in either treatment group at 4 weeks.
There was a significant (P<0.01) reduction in baPWV from
baseline at 8 weeks and there was a grouptime interaction
(P<0.05) in the blueberry group, whereas there were no
changes in the control group. There was no significant effect
of blueberry supplementation on mean arterial pressure,
cfPWV, and heart rate at any time point.
Blood Biomarkers
Blood biomarkers are presented in Table 4. There were no
significant changes in C-reactive protein levels at any time
point in either treatment group. SOD levels were significantly
(P<0.01) increased at 4 and 8 weeks compared with baseline
in the blueberry and control groups. Nitric oxide levels were
significantly (P<0.01) increased in the blueberry group at 8
weeks compared with baseline values, whereas there were
no changes in the control group.
DISCUSSION
We found that daily incorporation of freeze-dried blueberry
powder into the diet of postmenopausal women with pre-
and stage 1-hypertension for 8 weeks improves blood pres-
sure and arterial stiffness potentially through enhanced nitric
oxide-mediated vasodilation. To our knowledge, this is the
first study to evaluate the effects of blueberries on arterial
function as was done in this study, as well as in this study
population.
In terms of the effects of blueberries on blood pressure, the
results of the present study showed 5.1% and 6.3% reductions
in mean systolic SBP and DBP, respectively, in the blueberry
group, whereas there were no significant decreases in the
control group. These findings are in agreement with Basu and
colleagues
29
who noted a 6% and 4% reduction in SBP and
DBP, respectively, after 8 weeks of supplementation with 50 g
freeze-dried blueberry powder in middle-aged obese men
and women with metabolic syndrome. Therefore, the current
findings support that regular blueberry consumption, even in
a different study population, is effective in lowering blood
pressure. On the contrary, the consumption of 250 g blue-
berries by adult smokers for 3 weeks produced no changes in
blood pressure in a study by McAnulty and colleagues.
33
Several studies have shown that smokers respond differ-
ently than nonsmokers to dietary interventions,
34-36
which is
a possible reason for this observation. Another likely reason
for this finding is that the duration of their study was too
short to observe an effect on blood pressure as indicated by
no significant changes in blood pressure after 4 weeks of
treatment in the current study.
It is important to note that the findings of this study do not
suggest that the effectiveness of the dose of blueberry pow-
der used in this study matches that of antihypertensive
medications. This is evidenced by the fact that although
significant reductions were noted in SBP and DBP at 8 weeks
in the blueberry-treated group, mean SBP levels remained in
the prehypertensive range at the end of the treatment period.
It is possible that higher doses and/or longer intervention
time may result in further reductions in SBP to that of the
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372 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS March 2015 Volume 115 Number 3

normal range. However, the changes in blood pressure noted
in this study are of clinical significance because they
demonstrate that blood pressure can be favorably altered by
the addition of a single dietary component (eg, blueberries).
Pulse wave velocity is a noninvasive method for asses-
sing arterial stiffness and has been shown to predict
future cardiovascular events.
31
Epidemiologic
37,38
and clinical
intervention studies
39-41
have demonstrated that flavonoids
and flavonoid-rich foods are associated with improvements
in pulse wave velocity, and therefore, arterial stiffness. In the
current study, baPWV, which is a composite measure of
central (aortic) and peripheral arterial stiffness, was signifi-
cantly reduced after 8 weeks in the blueberry-treated group,
whereas there were no changes in the control group. baPWV
has been shown to be highly associated with cfPWV,
considered the gold standard measure of aortic stiffness,
and as such is an emerging index of central arterial
stiffness.
32,42,43
However, no changes were noted in cfPWV
Figure. Flowchart of enrollment and attrition in a study to examine the effects of daily blueberry consumption for 8 weeks on blood
pressure and arterial stiffness in postmenopausal women with pre- and stage 1-hypertension.
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March 2015 Volume 115 Number 3 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS 373

in either group. We have previously reported that dietary
interventions, including a hypocaloric diet
44
and supple-
mentation with watermelon
45
led to reduced baPWV but had
no effect on aortic pulse wave velocity. These findings, along
with the results of the current study, suggest that peripheral
arteries may be more responsive to dietary interventions
than central arteries.
Increased baPWV has been reported
46-48
to be predictive of
the progression of pre-hypertension to hypertension. Our
findings showing that blueberry consumption decreased SBP
and DBP following blueberry consumption may be explained
by the noted changes in baPWV. After 8 weeks, DBP moved
from the prehypertensive range to the normal blood pressure
range, whereas SBP remained in the prehypertensive range in
both groups, despite a significant reduction in SBP in the
blueberry-treated group. Hence, it can be suggested that daily
blueberry consumption may be effective in preventing the
progression of pre-hypertension to hypertension in post-
menopausal women, which may in part be explained by
improvements in arterial stiffness as indicated by reductions
in baPWV. Further, these findings are of additional clinical
significance because baPWV has been reported to be an
independent predictor of coronary atherosclerosis in post-
menopausal women.
49
Although the exact cause of hypertension is unknown, one of
the mechanisms leading to increased blood pressure and
arterial stiffness is suggested to be endothelial dysfunction. It is
known that oxidative stress leads to an increase in the pro-
duction of superoxide anions by NADPH oxidase, which is able
to react with nitric oxide to form peroxynitrate leading to a
reduction in nitric oxide bioavailability and endothelial dam-
age in the arteries.
12,13
As was mentioned earlier, it has been
demonstrated
30
that improvements in flow-mediated vaso-
dilation, indicative of enhanced endothelial function, were
closely associated with increases in circulating polyphenol
metabolites from blueberry consumption as well as decreases
in neutrophil NADPH oxidase activity, which would enhance
nitric oxide bioavailability. Although NADPH oxidase activity
or flow-mediated vasodilation was not assessed in the present
study, based on the results of previous studies it can be sug-
gested that the reductions in blood pressure and arterial
stiffness noted in the present study may have been due, in part,
to enhanced endothelial-dependent vasodilation. In the cur-
rent study, blueberry consumption increased nitric oxide
Table 3. The effects of 8 wk of supplementation with freeze-dried blueberry powder vs placebo on hemodynamic parameters at
baseline, 4 wk, and 8 wk in postmenopausal women with pre- and stage 1-hypertension
Variable
Blueberry Control
Baseline 4 wk 8 wk Baseline 4 wk 8 wk
meanstandard deviation!
Systolic blood pressure (mm Hg) 13814 13615 13117*
a
13815 13615 13915
Diastolic blood pressure (mm Hg) 8077710 759**
a
7887811 808
Mean arterial pressure (mm Hg) 9999711 9511 9899711 9711
Carotid-femoral pulse wave velocity (cm/sec) 1,234201 1,269225 1,254214 1,233238 1,241216 1,256229
Brachial-ankle pulse wave velocity (cm/sec) 1,498179 1,466203 1,401122**
a
1,470194 1,464174 1,477175
Heart rate (beats/min) 6510 669669667666656
a
P<0.05 for groupxtime interaction.
*P<0.05 for within-group differences in comparison with baseline.
**P<0.01 for within-group differences in comparison with baseline.
Table 2. Characteristics of study participants assessed in an 8-wk clinical trial evaluating the effects of freeze-dried blueberry
powder supplementation vs placebo on blood pressure and arterial stiffness in postmenopausal women with pre- and stage 1-
hypertension
Variable
Blueberry Control
Baseline 4 wk 8 wk Baseline 4 wk 8 wk
meanstandard deviation
a
!
Age (y) 59.74.58 ——57.34.76 ——
Height (cm) 1645.32 ——165.488.35 ——
Weight (kg) 82.118.52 82.218.18 82.118.21 88.421.39 90.320.44 88.421.72
Body mass index 30.15.94 30.25.90 30.25.96 32.76.79 32.76.54 32.16.82
Waist circumference (cm) 10516.60 9918.01 10314.76 9819.83 11038.32 10119.17
a
Baseline values were not significantly different between groups. There were no significant within-group changes for weight, body mass index, or waist circumference for either group.
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levels compared with no significant changes in the control
group. Although there were significant increases in SOD at 4
and 8 weeks in the blueberry group, these changes were also
observed in the control group. These findings suggest that
blueberry consumption per se may not influence the
bioavailability of nitric oxide through the dismutation of su-
peroxide by SOD but rather may influence nitric oxide pro-
duction. In fact, it has been demonstrated that flavonoids
improve endothelium-dependent vasodilation through endo-
thelial production of nitric oxide and not through superoxide
production.
50
As mentioned above, SOD levels were increased
at 4 and 8 weeks compared with baseline corresponding values
in both the blueberry-treated group and the control group.
Unfortunately, we cannot offer a reasonable explanation for
this phenomenon other than a time effect. Nonetheless, this is
speculative and needs confirmation in future studies. In terms
of blood pressure regulation, nitric oxide is produced from the
amino acid L-arginine by endothelial nitric oxide synthase in
the endothelium, the inner layer of the blood vessels. However,
nitric oxide can also be produced by inflammatory cells
through inducible nitric oxide synthase and neuronal nitric
oxide synthase.
51
Because there were no significant increases
in the inflammatory marker measured (ie, C-reactive protein)
and SBP and DBP levels were reduced at 8 weeks, it can be
suggested that the increase in nitric oxide levels was not
related to inducible nitric oxide synthase but rather endothe-
lial nitric oxide synthase.
Our study has several possible limitations. First, the study
duration was relatively short and it is unclear whether a longer
intervention period would result in greater reductions in blood
pressure and arterial stiffness, as well as a reduction in cfPWV.
Second, this study only assessed one dose of blueberry powder
and it would be beneficial to compare different doses to
identify any possible doseeresponse relationship. Third,
because freeze-dried blueberry powder was used as the
intervention and not fresh blueberries, it is difficult to assume
that freeze-dried blueberries are as effective as the fresh
berries and therefore future studies are needed to investigate
this. However, among the various methods of processing
berries, freeze-drying berries, including blueberries, has been
reported to cause the least loss of key nutrients, including total
polyphenols, anthocyanins, and antioxidant activity than other
forms of processing.
52
In addition, it was recently reported
53
that although processing blueberries (eg, freeze-drying for
use in baked products) significantly reduced anthocyanin
content, it led to an increase in the content of other
polyphenols, including chlorogenic acid and flavanol dimers
and trimers and exerted the similar postconsumption vascular
effects (eg, improved flow-mediated vasodilation). Fourth,
because the sample size and power were calculated based on
changes in blood pressure, it is possible that the study was not
adequately powered to detect differences in other parameters
of interest. Fifth, although an initial 3-day food record was
obtained from participants at the beginning of the study, this
was not done at the end of the study and should be considered
a limitation. In addition, physical activity was not assessed
throughout the duration of the study. However, study partici-
pants agreed not to change their diets or physical activity
patterns for the duration of the study. Another limitation of the
study is that the blueberry and placebo powders were not
analyzed for nutrient composition in a double-blind fashion
but rather the study was single-blind. Finally, the population
used for the study was a specific population of postmenopausal
women with pre- and stage 1-hypertension and, therefore, the
results of the present study are not generalizable to other
populations.
CONCLUSIONS
Blueberry consumption may help in reducing both SBP and
DBP and improving arterial stiffness in postmenopausal
women with pre- and stage 1-hypertension, in part, through
increasing the production of nitric oxide and its vasodilatory
effect. This suggests that regular consumption of blueberries
over the long term could potentially delay the progression of
hypertension and reduce cardiovascular risk in post-
menopausal women. Nonetheless, freeze-dried blueberry
powder was used as the intervention in the present study.
We speculate that the consumption of fresh blueberries
would produce similar effects as those observed in this study,
although this needs confirmation. In addition, this study was
8 weeks in duration and it remains unknown whether in-
terventions longer than 8 weeks, less frequent blueberry
consumption, or lower portions would produce the same
results.
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meanstandard deviation !
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AUTHOR INFORMATION
S. A. Johnson is a postdoctoral fellow, Department of Nutrition, Food, and Exercise Sciences, and assistant director, Center for Advancing Exercise
and Nutrition Research on Aging, College of Human Sciences, Florida State University, Tallahassee; at the time of the study, she was a doctoral
degree candidate and study coordinator, Department of Nutrition, Food, and Exercise Sciences, Florida State University, Tallahassee. A. Figueroa
is an associate professor, and R. G. Feresin and M. L. Elam are doctoral degree candidates, all with the Department of Nutrition, Food, and Exercise
Sciences, Florida State University, Tallahassee. N. Navaei is a master’s degree bypass student and is a doctoral student, Department of Nutrition,
Food, and Exercise Sciences, Florida State University, Tallahassee; at the time of the study, she was a master’s degree student, Department of
Nutrition, Food, and Exercise Sciences, Florida State University, Tallahassee. A. Wong is an assistant professor, Department of Physical Education,
University of Puerto Rico - Mayaguez Campus, Mayaguez, Puerto Rico; at the time of the study, he was a doctoral candidate, Department of
Nutrition, Food, and Exercise Sciences, Florida State University, Tallahassee. R. Kalfon is a doctoral student, Department of Molecular Genetics,
Rappaport Family Institute for Research in the Medical Sciences, Technion-Israel Institute of Technology, Haifa, Israel; at the time of the study, he
was a master’s degree student, Department of Nutrition, Food, and Exercise Sciences, Florida State University, Tallahassee. L. T. Ormsbee is a
wellness coordinator, Campus Recreation, Florida State University, Tallahassee; at the time of the study, she was a study coordinator, Department
of Nutrition, Food, and Exercise Sciences, Florida State University, Tallahassee. S. Hooshmand is an assistant professor, School of Exercise and
Nutritional Sciences, San Diego State University, San Diego, California. M. E. Payton is department head and professor, Department of Statistics,
Oklahoma State University, Stillwater. B. H. Arjmandi is the Margaret A. Sitton Professor, Department of Nutrition, Food, and Exercise Sciences,
and director, Center for Advancing Exercise and Nutrition Research on Aging, College of Human Sciences, Florida State University, Tallahassee; at
the time of the study, he was also chair, Department of Nutrition, Food, and Exercise Sciences, Florida State University, Tallahassee.
Address correspondence to: Bahram H. Arjmandi, PhD, RD, Department of Nutrition, Food, and Exercise Sciences, College of Human Sciences,
Florida State University, 412 Sandels Bldg, Tallahassee, FL 32306. E-mail: barjmandi@fsu.edu
STATEMENT OF POTENTIAL CONFLICT OF INTEREST
No potential conflict of interest was reported by the authors.
FUNDING/SUPPORT
This study was supported by the US Highbush Blueberry Council/US Department of Agriculture.
ClinicalTrials.gov identifier: NCT01686282.
ACKNOWLEDGEMENTS
The results of this study were presented at the Scientific Sessions and Annual Meeting of the American Society for Nutrition at Experimental
Biology, April 26-27, 2013, San Diego, CA. The authors thank Yitong Zhao, MS, and Neda Akhavan, MS, for their contributions to data collection
and analysis.
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