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The Journal of Nutrition
Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions
Blueberries Decrease Cardiovascular Risk
FactorsinObeseMenandWomenwith
Metabolic Syndrome
1–3
Arpita Basu,
4
*MeiDu,
6
MistiJ.Leyva,
5
Karah Sanchez,
4
Nancy M. Betts,
4
Mingyuan Wu,
6
Christopher E. Aston,
5
and Timothy J. Lyons
5,6
4
Nutritional Sciences, Oklahoma State University, Stillwater, OK 74078;
5
General Clinical Research Center, University of Oklahoma
Health Sciences Center, Oklahoma City, OK 73117; and
6
Harold Hamm Oklahoma Diabetes Center and Section of Endocrinology and
Diabetes, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104
Abstract
Among all fruits, berries have shown substantial cardio-protective benefits due to their high polyphenol content. However,
investigation of their efficacy in improving features of metabolic syndrome and related cardiovascular risk factors in obesity is
limited. We examined the effects of blueberry supplementation on features of metabolic syndrome, lipid peroxidation, and
inflammation in obese men and women. Forty-eight participants with metabolic syndrome [4 males and 44 females; BMI:
37.8 62.3 kg/m
2
; age: 50.0 63.0 y (mean 6SE)] consumed freeze-dried blueberry beverage (50 g freeze-dried blueberries,
;350 g fresh blueberries) or equivalent amounts of fluids (controls, 960 mL water) daily for 8 wk in a randomized controlled
trial. Anthropometric and blood pressure measurements, assessment of dietary intakes, and fasting blood draws were
conducted at screening and at wk 4 and 8 of the study. The decreases in systolic and diastolic blood pressures were greater in
the blueberry-supplemented group (26and24%, respectively) than in controls (21.5 and 21.2%) (P,0.05), whereas the
serum glucose concentration and lipid profiles were not affected. The decreases in plasma oxidized LDL and serum
malondialdehyde and hydroxynonenal concentrations were greater in the blueberry group (228 and 217%, respectively) than
in the control group (29and29%) (P,0.01). Our study shows blueberries may improve selected features of metabolic
syndrome and related cardiovascular risk factors at dietary achievable doses. J. Nutr. 140: 1582–1587, 2010.
Introduction
Nutritional epidemiology provides some evidence regarding the
cardio-protective effects of foods high in polyphenols, such as
berries, tea, soy, and cocoa products (1–4). Blueberries are
particularly high in polyphenolic flavonoids in addition to
containing significant amounts of micronutrients and fiber (5–
7). American blueberries include the lowbush or wild blueberry
(Vaccinium angustifolium Aiton) and the highbush or cultivated
blueberry (Vaccinium corymbosum L.), both of which have
superior ranking among fruits and vegetables for their antiox-
idant capacity, mainly due to their high anthocyanin content
(93–235 mg/100 g berries) (6,7). In a comprehensive analysis of
the antioxidant potential of commonly consumed polyphenol-
rich beverages in the United States, blueberry juice was ranked
among the top 4 contributors of dietary antioxidants after
pomegranate juice, red wine, and concord grape juice (8).
Berries have been commercialized as fresh or frozen whole fruits,
freeze-dried berries, puree, juice, or wine (9–11). Although most
processing methods cause a significant decrease in the anthocy-
anin content (10–12), freeze-drying has been reported to cause
the least reduction in total polyphenol content of berries (11).
Several mechanistic studies provide evidence of antioxidative
(13,14), antiinflammatory (14,15), antihypertensive (16,17),
antidiabetic (18,19), antiobesity (20), and antihyperlipidemic
(20,21) effects of blueberries, providing possible rationale for
cardio-protective mechanisms. Based on these mechanistic
studies, consuming blueberries might favorably alter individual
components of metabolic syndrome, a rapidly escalating public
health problem in the US (22). Metabolic syndrome has been
characterized by abdominal adiposity, dyslipidemia (high tri-
glycerides, low HDL cholesterol), hypertension, impaired glu-
cose tolerance, elevated oxidative stress, inflammation, and
increased risks for type 2 diabetes and atherosclerotic cardio-
vascular disease (CVD)
7
(22–24). Berry supplementation using
1
Supported by the US Highbush Blueberry Council and by the University of
Oklahoma Health Sciences Center General Clinical Research Center grant
M01-RR14467, National Center for Research Resources, NIH.
2
Author disclosures: A. Basu, M. Du, M. J. Leyva, K. Sanchez, N. M. Betts,
M. Wu, C. E. Aston, and T. J. Lyons, no conflicts of interest.
3
Supplemental Tables 1 and 2 are available with the online posting of this paper
at jn.nutrition.org.
* To whom correspondence should be addressed. E-mail: arpita.basu@okstate.edu.
7
Abbreviations used: CRP, C-reactive protein; CVD, cardiovascular disease;
HbA
1C
, hemoglobin A
1C
; HNE, hydroxynonenal; IL-6, interleukin-6; MDA,
malondialdehyde; MPO, myeloperoxidase; ox-LDL, oxidized LDL; RD, registered
dietitian; sICAM-1, soluble intercellular adhesion molecule-1; sVCAM-1, soluble
vascular cell adhesion molecule-1.
ã2010 American Society for Nutrition.
1582 Manuscript received March 26, 2010. Initial review completed April 8, 2010. Revision accepted June 29, 2010.
First published online July 21, 2010; doi:10.3945/jn.110.124701.
chokeberries, cranberries, or a combination of berries has been
shown to improve features of metabolic syndrome such as
dyslipidemia, hypertension, or impaired fasting glucose in
participants with existing cardiovascular risk factors (25–27).
However, there is a paucity of clinical data on the cardiovascular
health benefits of blueberries per se.
Thus, this study was designed to test the hypothesis that
blueberry supplementation, in the form of a freeze-dried
beverage, will improve features of metabolic syndrome and
decrease biomarkers of lipid and lipoprotein oxidation and
inflammation in study participants compared with a control
group consuming equivalent amounts of fluids, in a randomized
controlled trial.
Materials and Methods
Participants. Sixty-six obese men and women with metabolic syndrome
(mean age, 50.0 63.0 y) were enrolled in this randomized controlled
study. They were screened for the qualifying criteria: 3 of 5 features of
metabolic syndrome as defined by the National Cholesterol Education
Program, Adult Treatment Panel (22). Recruitment and interventions
were conducted at the General Clinical Research Center at the University
of Oklahoma Health Sciences Center, and at the Nutritional Sciences
Clinical Assessment Unit at Oklahoma State University. Participants
were recruited through flyers and campus e-mail advertisements at both
sites. Each potential recruit received an initial telephone screening prior
to the screening visit. They were excluded if they were younger than 21 y
of age; taking medications for any chronic disease, including hypogly-
cemic, hypolipidemic, antiinflammatory, or steroidal medications; or
had liver, renal, or thyroid disorders or anemia. Potential recruits also
were excluded if they were consuming antioxidants or fish oil supple-
ments on a regular basis, were current smokers, consuming alcohol on a
regular basis (except social drinking ;1–2 drinks/wk), or were pregnant
or lactating. This intervention study was approved by the Institutional
Review Board at the University of Oklahoma Health Sciences Center and
at Oklahoma State University. All participants provided written in-
formed consent.
Intervention. Freeze-dried blueberries provided by the US Highbush
Blueberry Council (Folsom, CA) were a blend of 2 blueberry cultivars,
Tifblue and Rubel, in a 1:7 ratio of freeze-dried:fresh berries, with no
additives (Table 1). Participants receiveda daily dose of 50 g freeze-dried
blueberries that were reconstituted in 480 mL water and vanilla extract
or Splenda was added based on the preference of the participants. The
participants were asked to consume 1 cup (240 mL) in the morning and
the second in the evening at least 6–8 h apart. Because the beverage made
with reconstituted freeze-dried blueberries was thick and sticky in
consistency, participants were also asked to rinse out each cup with an
additional cup of water, thus leading to the consumption of ~960 mL
fluids/d in the blueberry group. The control group was asked to consume
960 mL water to match the fluid intake of the blueberry group and was
provided with containers to measure out the prescribed amount of water.
Study design. This was a single-blinded controlled study in which
participants were randomized to the blueberry or control group for 8 wk.
Those in the blueberry group made 3 visits/wk to their study site
(Monday, Wednesday, and Friday) to ensure compliance by consuming
the first cup in the morning under observation by the research staff.
Participants were instructed to keep the drink under refrigeration, to
avoid exposing it to direct heat or light, and to avoid consuming it with
any other snack or with lunch or dinner, because other foods might
interfere with the absorption of the blueberry polyphenols. Participants
were asked to return any unconsumed blueberry drink. Controls were
provided with containers to measure 4 cups water to be consumed on a
daily basis. All participants returned for follow-up visits at 2, 4, 6, and 8 wk
of the study. The research staff were instructed not to discuss diet or
weight issues with participants consuming blueberries to avoid potential
confounding factors that might arise as a result of frequent visits of the
blueberry group (compared with the biweekly visits of the control
group). Participants received monetary compensation during their
follow-up visits. They were asked to refrain from consuming any other
source of berries or related products derived from berries such as juices,
jams, and desserts. They were also asked to refrain from consuming
green tea, cocoa, and soy products while participating in the study,
because these were the most commonly consumed flavonoid-rich foods
by the enrolled participants as identified by a screening FFQ specific for
flavonoids. Participants maintained their usual diet, physical activity,
and lifestyle while on the study and were also asked to record their food
intakes. Body weight, height, waist circumference, and systolic and
diastolic blood pressures were measured by trained personnel and blood
draws were performed by registered nurses at screening and wk 4 and 8
of the study. All laboratory staff were unaware of treatment groups.
Anthropometrics and blood pressure. Participants removed shoes
and items in dress pockets and were weighed on a flat, uncarpeted
surface with the SECA 644 Multifunctional Hand Rail Scale (SECA) and
recorded to the nearest 0.1 kg. Height was measured without shoes using
the Accustat Genentech Stadiometer and recorded to the nearest 0.1 cm.
Systolic and diastolic blood pressures were measured in millimeters Hg
using Spot Vital Signs Device (Welch Allyn). Participants were asked to
lie down and relax for ~8–10 min, following which 3 blood pressure
measurements were recorded at intervals of 5 min. Waist circumference
was measured at the superior iliac crest using the Gulick II Tape Measure
(Vital Signs). All measurements were conducted in fasting participants at
screen and at wk 4 and 8 of the study.
Dietary analyses. Study participants were required to record daily food
intake for 3 d at 3 time points throughout the study: screen and wk 4 and
8. Each time, the registered dietitian (RD) carefully instructed the
participants on accurate food record completion using visual tools such
as food models and common household measuring utensils. Instructions
were also given on careful recording of details needed for recipes. Three
day averages of micro- and macronutrient intakes were analyzed using
Nutritionist Pro (version 3.2, 2007, Axxya Systems). All data entry was
performed by RD trained and certified in using the software. All dietary
data entry was verified by a second RD as a measure of quality control. If
a participant ate a food that was not in the database, a food with very
similar nutrient composition was chosen. Nutrient information was also
obtained through food labels or recipes from participants, online
sources, or at grocery stores.
Clinical analyses. Blood samples were collected immediately after each
draw and serum was transported to the University of Oklahoma Medical
Center Laboratory for analyses of fasting glucose, insulin, lipid profile
(total cholesterol, triglycerides, LDL cholesterol, and HDL cholesterol),
TABLE 1 Composition of freeze-dried blueberries
1
Nutrients/antioxidant activity unit/50 g
Energy,
2
kcal 174.0
Protein, g1.7
Carbohydrates, g42.3
Total sugars, g30.0
Dietary fiber, g9.3
Vitamin C, mg 86.0
Calcium, mg 15.0
Iron, mg 0.5
Potassium, mg 204.0
Sodium, mg 8.0
Phenolic components, mg 1624
Anthocyanins, mg 742
Oxygen radical absorbance capacity, mmol TE 17.8
1
Source: U.S. Highbush Blueberry Council (Folsom, CA). Fresh weight replacement:
1 to 7 (freeze-dried to fresh).
2
1 kcal = 4.184 kJ.
Blueberries and metabolic syndrome 1583
and other blood variables, including safety variables (hemoglobin,
platelets, white blood cells, liver enzymes, creatinine, blood urea
nitrogen, electrolytes, albumin, total protein, and thyroid-stimulating
hormone), using automated diagnostic equipment (Abbott Architect
Instruments) following standard protocols at the University of Okla-
homa Medical Center. Serum hemoglobin A
1C
(HbA
1C
) was analyzed
using a DCA 2000+ (Bayer). Insulin resistance was evaluated by
homeostasis model assessment calculated as [fasting insulin (mU/L) 3
fasting glucose (mmol/L)]/22.5.
For assays to determine serum malondialdehyde (MDA) and
hydroxynonenal (HNE) and plasma oxidized-LDL, myeloperoxidase
(MPO), adiponectin, interleukin-6 (IL-6), high sensitivity C-reactive
protein (CRP), soluble intercellular adhesion molecule-1, and soluble
vascular cell adhesion molecule levels, serum and EDTA-plasma samples
were collected, separated by centrifugation at 1800 3gfor 10 min at
48C, and stored at 2808C for subsequent analyses. NMR-determined
lipoprotein subclass profile was performed in first-thaw plasma speci-
mens using a 400-MHz proton NMR analyzer at LipoScience as
described previously (28).
Biomarkers of oxidative stress. Plasma concentrations of MPO and
ox-LDL were measured in duplicate with commercially available ELISA
kits: Mercodia MPO ELISA and Mercodia Oxidized LDL Competitive
ELISA (Mercodia) according to the manufacturer’s instructions. Lipid
peroxidation was measured in serum as combined MDA and HNE using
a colorimetric assay according to the manufacturer’s protocol (LPO-586,
Oxis Health Products). The mean intra-assay CV for MPO, ox-LDL, and
MDA and HNE were 4.8, 5.2, and 3.6%, respectively.
Biomarkers of inflammation. Plasma concentrations of CRP, adipo-
nectin, IL-6, soluble intercellular adhesion molecule-1 (sICAM-1), and
soluble vascular cell adhesion molecule-1 (sVCAM-1) were determined
using commercially available ELISA kits: Human CRP Quantikine
ELISA, Human Total Adiponectin Quantikine ELISA, Human IL-6
Quantikine ELISA, Human sICAM-1 Quantikine ELISA, and Human
sVCAM-1 Quantikine ELISA (R&D Systems) according to the manu-
facturer’s protocols. The minimum detectable levels were 15.6, 62.5,
9.4, 15.6, and 15.6 ng/L for each assay, respectively. The inter-assay CV
were 6.2, 3.6, 3.1, 3.5, and 7.6%, respectively.
Statistical analyses. For all measures, descriptive statistics were
calculated and graphs drawn to look for outliers; no data points were
determined to be outliers. Differences between blueberry and control
groups at baseline were assessed using Student’s ttests.
Changes in measurements over the 8-wk study period were assessed
by calculating the difference between the pre- and postintervention
measurements in each group. For each variable, significance was assessed
by comparing the change over the 8-wk study period between blueberry
and control groups using Student’s ttests. Target sample size was
calculated to include 25 participants/group to detect significant differ-
ences in certain dependent variables with 80% power. Multiple
hypothesis testing was not accounted for and all statistical tests were
2-tailed with significance level set at 0.05. SPSS for Windows (version
15.0, SPSS, 2006) was used for the statistical calculations.
Results
In this randomized controlled trial, 66 men and women with
metabolic syndrome were enrolled upon qualification. Among
34 enrolled participants in the blueberry group, 9 withdrew on
account of side effects, including nausea, vomiting, constipation,
and diarrhea following blueberry intervention during the first
week of the study, leading to a 27% drop-out rate in the
blueberry group. Among 32 participants enrolled in the control
group, 1 was excluded on account of smoking, 6 withdrew due
to personal reasons (not disclosed), and 2 withdrew due to time
constraints, leading to a 28% drop-out rate in the control group.
The temporary gastrointestinal discomfort was also reported by
participants who completed the 8-wk blueberry treatment,
which did not persist beyond the first week of the intervention.
Thus, 48 participants actually completed the 8-wk study of
whom 25 were in the blueberry group and 23 were controls.
Baseline characteristics, including age, BMI, and safety varia-
bles, did not differ between the blueberry and control groups
(Table 2). For the 25 participants in the blueberry group,
compliance was high, with 96.5% of the blueberry drink
consumed and 100% compliance visits/wk. The controls
reported 100% compliance in terms of water intake and
biweekly visits.
The decreases in systolic and diastolic blood pressures were
greater in the blueberry-supplemented group (26 and 24%,
respectively) than in controls (21.5 and 21.2%) (P= 0.003 and
P= 0.04). Changes in body weight, waist circumference, HbA
1C
,
insulin resistance, and serum glucose concentration and lipid
profile did not differ between the groups. Blood pressure
outcomes remained significantly different when data were
analyzed without participants on stable antihypertensive med-
ications in the blueberry and control groups. Those in the
blueberry group had a significantly lower baseline serum LDL-
cholesterol concentration than controls and no significant
changes were noted between groups (Table 3). NMR-based
lipid particle concentrations were not significantly affected by
blueberry intervention (Supplemental Table 1).
The decreases in oxidized LDL (ox-LDL) and combined
MDA and HNE concentrations were greater in the blueberry-
supplemented group (228 and 217%, respectively) than in
controls (29 and 29%) (P= 0.009 and P= 0.005). Changes in
plasma CRP, IL-6, MPO, adhesion molecules (sICAM-1,
sVCAM-1), and adiponectin concentrations did not differ
between the groups (Table 4).
Changes in dietary intakes did not differ between the
blueberry and control groups (Supplemental Table 2).
Discussion
An emerging body of evidence indicates the role of blueberries as
cardio-protective agents, although few human studies have been
reported to support this claim. Our test dose of 50 g freeze-dried
blueberries, equivalent to ~350 g or 2.3 cups fresh blueberries,
TABLE 2 Baseline characteristics and serum biomarkers of
participants with metabolic syndrome completing
8-wk supplementation with freeze-dried blueberries
or control treatment
1
Blueberry Control
n25 23
Age, y51.5 63.0 48.0 63.3
BMI, kg/m
2
38.1 61.5 37.5 63.0
M/F n/n 2/23 2/21
Aspartate aminotransferase, U/L 25.3 61.3 25.7 63.0
Alanine aminotransferase, U/L 33.1 62.6 34.0 64.7
Blood urea nitrogen, mmol/L 4.6 60.2 4.2 60.4
Creatinine, mmol/L 70.7 68.8 80.0 618.0
Albumin, g/L 41.0 61.0 35.0 62.0
Hemoglobin, g/L 138.0 62.0 143.0 62.0
White blood cells, n310
29
7.0 60.4 6.8 60.5
Antihypertensive medication users, %22.0 21.0
Multivitamin users, %12.0 10.0
1
Data are means 6SE.
1584 Basu et al.
was overall well tolerated and conforms to the daily fruit and
vegetable recommendations of at least 5 servings for US adults
(29). We also selected this dose to investigate the therapeutic
effects of blueberries in a standard freeze-dried form on features
of metabolic syndrome in men and women with low fruit intake
(30).
Blueberries have been reported to exert favorable effects on
features of metabolic syndrome and type 2 diabetes in animal
models of obesity (19,20). Human intervention studies investi-
gating the effects of berries on metabolic syndrome are limited.
Clinical trials involving chokeberry juice supplementation
showed significant improvements in fasting glucose, lipids, and
HbA1c in type 2 diabetics, and, cranberry, or bilberry and black
currant extract supplementations, were shown to improve
dyslipidemia in type 2 diabetics, or hyperlipidemic patients,
respectively (25,26,31). However, in our study, blueberry
supplementation for 8 wk did not affect fasting serum glucose,
insulin, lipid profiles, and body weight or waist circumference.
These null effects may be due to the fact that participants with
metabolic syndrome in our blueberry intervention group had
normal baseline levels of glucose, insulin, and lipids (except low
HDL cholesterol). Also, additional dietary adjustments and
longer study duration may be needed to affect adiposity in these
men and women. On the other hand, blueberry supplementation
significantly decreased systolic and diastolic blood pressures in
our prehypertensive participants, which conforms to the findings
of previous studies on the blood pressure-lowering effects of
cranberry intervention in healthy humans or mixed berry
supplementation in those with CVD risk factors (27,32).
Mechanistic studies explain the role of blueberries or anthocy-
anins in ameliorating hypertension by significantly increasing
endothelial nitric oxide synthase levels in bovine and human
endothelial cells (33,34), decreasing vasoconstriction via nitric
oxide-mediated pathway, or decreasing renal oxidative stress
and, thereby, systolic blood pressure in rodent models of human
essential hypertension (16,17). Thus, our study is the first to our
knowledge to report that blueberries have antihypertensive
effects in people with metabolic syndrome. Because hyperten-
sion is an independent and significant CVD risk factor (35) and
can be mitigated by dietary practices (36), blueberry supple-
mentation may be a potential therapeutic dietary measure and
needs further confirmation in larger controlled studies.
Biomarkers of lipid and lipoprotein oxidation such as MDA
and ox-LDL levels are elevated in population with abdominal
adiposity and metabolic syndrome and have also been associated
with coronary artery disease (24,37,38). In our 8-wk study,
decreases in plasma ox-LDL and serum MDA and HNE levels
were significantly greater in the blueberry-supplemented group
than in controls. Our findings are similar to the previous
intervention studies reporting the effects of blueberries, cran-
berry juice, or freeze-dried strawberries in lowering lipid
hydroperoxides in smokers, ox-LDL in healthy volunteers, or
MDA and HNE in women with metabolic syndrome, respec-
tively (39–41). The antioxidant effects of blueberries have also
been reported by studies using cellular and animal models of
oxidative stress (13,14), thus providing mechanistic evidence
that needs to be strengthened by larger controlled clinical trials.
However, in our study, blueberries did not affect plasma MPO,
an independent predictor of CVD and a significant contributor
to oxidative stress (42). Thus, further investigation is needed to
define the effects of berry polyphenols on MPO in participants
with metabolic risk factors.
Biomarkers of inflammation such as CRP, IL-6, and adhesion
molecules ICAM-1 and VCAM-1 are significantly elevated in
metabolic syndrome and positively associated with CVD
(43,44). On the other hand, adiponectin, an antiinflammatory
cytokine, is significantly decreased in metabolic syndrome and
inversely related to CVD (45). The antiinflammatory effects of
berries have been suggested by limited epidemiological obser-
vations. The Women’s Health Study showed a borderline
significant risk reduction of elevated CRP ($3 mg/L) among
women consuming higher amounts of strawberries [$2 servings/
wk (150 g/wk)], whereas blueberry intake had no significant
association with risks of CVD, including CRP levels (46).
Analyses of NHANES data (1999–2002) also revealed a
significant inverse association between serum CRP and antho-
cyanin intakes among U.S. adults (47). In our study, changes in
plasma levels of adhesion molecules, CRP, IL-6, and adiponectin
did not differ between the blueberry and control groups. In a
recently reported study, Curtis et al. (48) showed similar null
effects of elderberry anthocyanin extracts on inflammatory
biomarkers such as CRP and IL-6 in healthy postmenopausal
women in a 12-wk study. Thus, longer study duration or a higher
dose of berry polyphenols may be needed to lower inflammatory
TABLE 3 Change in anthropometrics, blood pressure,
and serum glucose and lipid concentrations
in participants with metabolic syndrome after
8-wk supplementation with freeze-dried
blueberries or control treatment
1
Variable
D(0–8 wk)
Blueberry Control
n25 23
Body weight, kg 20.4 60.30 0.5 60.40
Waist circumference, cm 20.4 60.30 20.5 61.10
Systolic blood pressure, mm Hg 27.8 62.50* 22.0 62.80
Diastolic blood pressure, mm Hg 22.5 61.10* 0.7 62.00
Glucose, mmol/L 0.1 60.20 20.1 60.20
HbA
1C
,%0.1 60.10 0.2 60.10
Homeostasis model assessment
of insulin resistance
0.7 60.50 20.2 60.20
Triglycerides, mmol/L 0.0 60.10 0.1 60.20
Total cholesterol, mmol/L 0.2 60.20 0.2 60.30
HDL cholesterol, mmol/L 0.0 60.02 0.0 60.02
LDL cholesterol, mmol/L 0.1 60.10 0.0 60.20
1
Data are means 6SE. *Different from control, P,0.05.
TABLE 4 Change in plasma biomarkers of oxidative stress and
inflammation in participants with metabolic syndrome
after 8-wk supplementation with freeze-dried
blueberries or control treatment
1
Variables
D(0–8 wk)
Blueberry Control
n25 23
CRP, mg/L 0.2 60.50 0.4 61.50
sICAM-1, ng/L 20.1 60.02 0.0 60.03
sVCAM-1, ng/L 20.1 60.04 0.0 60.05
IL-6, pg/L 0.0 60.01 0.0 60.01
Adiponectin, mg/L 0.0 60.01 0.0 60.01
ox-LDL, U/L 230.0 64.00* 29.6 69.50
MPO, mg/L 2.5 65.00 22.4 68.50
MDA and HNE, mmol/L 20.2 60.03* 20.1 60.01
1
Data are means 6SE. *Different from control, P,0.01.
Blueberries and metabolic syndrome 1585
biomarkers. Berry extracts or anthocyanin treatment has been
shown to reduce inflammation-related parameters in animal and
cellular models (14,15). Thus, further investigation is needed to
define the antiinflammatory effects of berries or anthocyanins in
cases of obesity and metabolic syndrome.
Certain limitations of our study include a cohort comprised
primarily of women, the side effects and drop-outs following
blueberry intervention, and the absence of a dose-response
treatment. The gastrointestinal side effects were anticipated as a
result of additional fiber intake in the form of a concentrated
berry powder, especially in our participants with habitual low
fiber and fruit intakes (Supplemental Table 2) (30). Though it led
to a 27% drop-out rate in the blueberry arm, those who
completed the entire 8-wk study also experienced this temporary
gastrointestinal discomfort during the first week, which was
later alleviated, and participants reported high compliance to the
blueberry beverage. For future studies, administration of
reconstituted freeze-dried blueberries in 3 or 4 doses throughout
the day, or using 2 cups conventional frozen blueberries, as well
as dietary adjustments for total fiber intake may have improved
tolerability while exerting similar health benefits. Also, we did
not detect parent anthocyanins or metabolites in serum samples
as a measure of compliance, mainly because blood draws were
conducted in a 10- to 12-h fasting state, which allows complete
clearance and excretion of anthocyanins (49). Finally, our
control group was consuming plain water to match the fluid
intake of the intervention group, whereas a fiber- and energy-
matched control beverage may lead to better elucidation of the
role of polyphenols in the observed health effects of berries.
In conclusion, our study findings suggest a cardio-protective
role of dietary achievable doses of blueberries in men and
women with metabolic syndrome, which includes a significant
decrease in systolic and diastolic blood pressures and plasma
ox-LDL and lipid peroxidation. Our clinical data are supported
by previously reported mechanistic studies and limited human
intervention studies using single or mixed berries or anthocyanin
extracts. However, our findings specifically show the cardio-
protective effects of blueberries in improving features of
metabolic syndrome. These results warrant further investigation
and provide some evidence for including blueberries as part of
healthy dietary practices.
Acknowledgments
A.B., C.E.A., and T.J.L. designed the intervention study; M.D.,
M.J.L., K.S., M.W., and A.B. conducted research and labora-
tory measurements; C.E.A. and N.M.B. analyzed data; and
A.B., C.E.A., and T.J.L. wrote the paper. All authors read and
approved the final manuscript.
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