By Traci Pantuso ND, MS
Adjunct Faculty,
Bastyr University,
Seattle, WA;

Owner,
Naturopathic Doctor,
Harbor Integrative Medicine,
Bellingham, WA

Dr. Pantuso reports no financial relationships relevant to this field of study.

Summary Points

  • In postmenopausal women diagnosed with pre- or stage 1-hypertension, 22 grams of freeze-dried blueberry powder significantly improved both systolic and diastolic blood pressure after 8 weeks compared to baseline.
  • In addition, blueberry powder significantly improved arterial stiffness, which may be modulated through the significant increase in nitric oxide measured at 8 weeks, compared to baseline in the blueberry group.

SYNOPSIS: This randomized, double-blind, placebo-controlled study demonstrated that consumption of freeze-dried blueberry powder twice daily for 8 weeks improved blood pressure and measurements of arterial stiffness in postmenopausal women with pre- or stage 1 hypertension.

SOURCE: Johnson SA, et al. 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. J Acad Nutr Diet 2015; in press.

A randomized, double-blind, placebo-controlled clinical trial design was used to investigate the effects of freeze-dried blueberries on blood pressure and arterial stiffness in postmenopausal women with pre- or stage 1 hypertension (HTN) ( 125/85 mmHg and 160/90 mmHg). Eighty-one postmenopausal women between the ages of 45-65 years with pre- or stage 1-HTN were recruited in the greater Tallahassee, FL, area.

Women were excluded from the study if they were diagnosed with uncontrolled HTN (> 160/100 mmHg) or cardiovascular disease; were heavy smokers (> 20 cigarettes/day); were diagnosed with asthma, glaucoma, thyroid, kidney, liver, or pancreatic disease; had active cancer; or were receiving hormone replacement therapy or insulin. Forty-eight women who met the inclusion criteria were enrolled in the study and were instructed to not change their diet or physical activity pattern throughout the study.

The women were instructed to mix 11 grams of freeze-dried blueberry powder in water twice daily (the equivalent of 1 cup of fresh blueberries per day). The freeze-dried blueberry powder contained a 50/50 mix of Vaccinium virgatum and Vaccinium corymbosum high brush berries. The authors also instructed the women to mix in Splenda or vanilla for extra flavoring if required. The placebo powder contained artificial and natural blueberry flavoring, maltodextrin, fructose, artificial purple and red color, and citric acid and silica dioxide. The nutritional composition of both the freeze-dried blueberry powder and placebo powder were measured; however, the authors did not comment on whether a taste comparison was performed between the powders (see Table 1).

Table 1: Different Blueberry Preparations and Their Nutrient Compositions

 


Placebo
powder (22 g)

Freeze-dried
blueberry
powder (22 g)


Fresh blueberry
(1 cup)

Anthocyanins (mg/g)

0

4.69

Not measured

Phenolics (mg/g)

0

8.45

Not measured

Oxygen Radical Absorbance (µmol TEC/g)

0

80.52

Not measured

Potassium (mg)

0

103.18

112

Calcium (mg)

0

7.50

9.00

Vitamin C (mg)

0

2.27

14.10

Protein (g)

0.17

0.59

1.08

Fiber (g)

0

4.73

3.50

Total Carb (g)

20.82

20.57

21.02

kCal

86

87

83

Adapted from: Johnson SA, et al. 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. J Acad Nutr Diet 2015; in press.

Blood pressure, height, weight, body mass index (BMI), and waist circumference were measured at baseline, 4-, and 8-week time points. Arterial stiffness was also measured as an outcome using a carotid-femoral pulse wave velocity and brachial ankle pulse wave velocity performed at baseline, 4, and 8 weeks. Pulse wave velocity is used to assess arterial stiffness and also may be used to predict future cardiovascular events. Nitric oxide (NO), superoxide dismutase (SOD), and C- reactive protein (CRP) were measured from blood samples taken at baseline, 4, and 8 weeks. Statistical analysis was performed using analysis of variance (ANOVA) models to detect statistical analysis between groups and over time, and P values < 0.05 were considered statistically significant.

Forty women completed the study, and 17% (20% for the treatment group and 13% for the control group) of women dropped out of the study due to noncompliance, medical, and health-related issues such as gastrointestinal complaints and personal reasons. The authors looked at differences between groups at the 0, 4-, and 8-week timepoints and analyzed with ANOVA.

No significant differences were detected in age, height, weight, BMI, or waist circumference between groups throughout study. No significant differences were detected at baseline for systolic blood pressure (SBP), diastolic blood pressure (DBP), and arterial stiffness measurements between groups.

SBP and DBP were significantly reduced by 5.1% (7 mmHg; P < 0.05) and 6.4% (5 mmHg; P < 0.01), respectively, in the blueberry group at 8 weeks compared to baseline (see Table 2).

No significant decrease in either SBP or DBP was noted in the control group (see Table 2). There was a significant decrease in the brachial ankle-pulse wave velocity at 8 weeks compared to baseline in the blueberry group (P < 0.01) (see Table 2). No change in the brachial-ankle pulse wave velocity was noted in the control group (see Table 2). There were no significant changes in CRP levels noted in either group during the study. SOD and NO levels were significantly increased at 8 weeks compared to baseline in the blueberry group (see Table 2). SOD levels in the control group were significantly changed at both 4 and 8 weeks, while no significant changes in NO levels were detected in the control group (see Table 2).

Table 2: Differences Between Blueberry and Control Groups

 

Blueberry

Control

Baseline

SBP: 138 ± 14

DBP: 80 ± 7

baPWV: 1498 ± 179

SOD: 0.21 ± 0.06

NO: 9.11 ± 7.95

SBP: 138 ± 15

DBP: 78 ± 8

baPWV: 1470 ± 194

SOD: 0.23 ± 0.05

NO: 9.81 ± 7.20

4 weeks

SBP: 136 ± 15

DBP: 77 ± 10

baPWV: 1466 ± 203

SOD: 0.36 ± 0.11**

NO: 13.86 ± 11.45

SBP: 136 ± 15

DBP: 78 ± 11

baPWV: 1464 ± 174

SOD: 0.40 ± 0.06**

NO: 9.20 ± 5.95

8 weeks

SBP: 131 ± 17*

DBP: 75 ± 9**

baPWV: 1401 ± 122**

SOD: 0.50 ± 0.22**

NO: 15.35 ± 11.16*

SBP: 139 ± 15

DBP: 80 ± 15

baPWV: 1,477 ± 175

SOD: 0.49 ± 0.15**

NO: 10.73 ± 5.63

Systolic blood pressure (SBP; mmHg), diastolic blood pressure (DBP; mm Hg), brachial-ankle pulse wave velocity (baPWV; cm/sec), superoxide dismutase (SOD; U/mL) and nitric oxide (NO; µM) levels.

*P < 0.05 for within group differences in comparison to baseline

**P < 0.01 for within group differences in comparison to baseline

Adapted from: Johnson SA, et al. 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. J Acad Nutr Diet 2015; in press.

Eight women dropped out of the study due to personal reasons, gastrointestinal issues, and non-compliance. The authors do not mention the number of women that discontinued the study for each particular reason.

COMMENTARY

This study demonstrated improvements in blood pressure and arterial stiffness in postmenopausal women with pre- or stage 1-HTN with consumption of 22 grams of freeze-dried blueberry powder (equivalent to 1 cup of blueberries per day) after 8 weeks compared to baseline. The BP findings may have been significant, with a 7/5 mmHg reduction in SBP/DBP, but it is important to compare to other clinically significant dietary lifestyle modifications that have been shown to reduce blood pressure. The DASH diet with sodium restriction has been shown to reduce BP 12/6 mmHg (SBP/DBP) in hypertensive adults, and the DASH diet without sodium restriction reduced BP 6/2 mmHg (SBP/DBP) in hypertensive adults over 14 weeks.1 Weight loss of 4.4-8.8 lbs (2-4 kg) has also been shown to decrease SBP in the range of 3-8 mmHg.2

NO is an important chemical mediator that is known to relax blood vessels and was increased in the blueberry group at 8 weeks compared to baseline.3 SOD levels were also significantly higher at 8 weeks compared to baseline in both the control and blueberry groups, making the validity of this finding questionable.

There are a number of limitations to this study, including the number of participants and the relatively short trial period. The number of participants was low, but comparable to many herbal studies and the authors discuss that because of this, the study may have been underpowered.

Eight women did not complete the study due to noncompliance, medical, and health-related issues such as gastrointestinal complaints, taste fatigue as the participants mixed the blueberry and placebo powder into their beverages, and personal reasons. The authors did not provide further detail; however, gastrointestinal complaints and taste fatigue as a result of the powder are important factors when recommending a freeze-dried powder for clinical use. This study did not control for physical activity, diet, or smoking, which are all HTN risk factors.4 In a previous 3-week study, blueberry consumption did not appear to have the same effect on lowering blood pressure in adult smokers.5 The women in this study were not excluded for smoking fewer than 20 cigarettes per day, which may have impacted the results of this study. The study was also funded by the U.S. Highbush Blueberry Council/U.S. Department of Agriculture, which provided the freeze-dried blueberry and placebo powders. Because the study population was postmenopausal women with pre- and stage 1-HTN, it is difficult to extrapolate the results of this study to other populations. However, a previous study investigating blueberry powder consumption in men and women with metabolic syndrome who were of middle age and obese demonstrated a reduction in SBP and DBP after 8 weeks of supplementation.6

The participants in this study consumed freeze-dried blueberry powder.; other studies have demonstrated high intakes of flavonoids, such as the anthocyanins found in blueberries, have been associated with a decreased risk of HTN and myocardial infarction incidence or prevalence.6,7 It is difficult to equivocate the effects that fresh blueberries would have compared to the freeze-dried powder from the results of this study. However, the authors note that freeze-drying blueberries has been shown to “cause the least loss of key nutrients.” The freeze-dried blueberry powder used in this study was made from 50/50 mix of V. virgatum and V. corymbosum high brush berries; which may or may not have the same bioflavanoid profile as blueberries that are easily obtained from the grocery store. Another factor to consider when recommending blueberry consumption is to specify that the berries should be organic, as they are ranked number 14 on the Environmental Working Group’s list of Fruits and Vegetables With Pesticide Residue Data.8

In summary, 1 cup of organic blueberries per day, fresh or frozen, combined with a dietary pattern such as the Mediterranean or DASH diet and adequate physical activity to maintain a healthy weight may improve hypertension and other cardiovascular risk factors.2-9 These recommendations should be considered as part of a preventive or treatment strategy for both healthy and hypertensive patients.

References

  1. Vollmer WM, et al. Effects of diet and sodium intake on blood pressure: subgroup analysis of the DASH-sodium trial. Ann Intern Med 2001;135:1019-1028.
  2. Harsha DW, Bray GA. Weight loss and blood pressure control (Pro). Hypertension 2008;51:1420-1425.
  3. Hermann M, et al. Nitric oxide in hypertension. J Clin Hypertens 2006;8(12 Suppl 4):17-29.
  4. Chobanian AV, et al. The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation and treatment of High Blood Pressure: The JNC 7 report. JAMA 2003;289:2560-2572.
  5. McAnulty SR, et al. Effect of daily fruit ingestion on angiotensin converting enzyme activity, blood pressure, and oxidative stress in chronic smokers. Free Radic Res 2005;39:1241-1248.
  6. Basu A, et al. Blueberries decrease cardiovascular risk factors in obese men and women with metabolic syndrome. J Nutr 2010;140:1582-1587.
  7. Cassidy A, et al. High anthocyanin intake is associated with a reduced risk of myocardial infarction in young and middle-aged women. Circulation 2013;127:188-196.
  8. Environmental Working Group. All 48 fruits and vegetables with pesticide residue data. Available at: http://www.ewg.org/foodnews/list.php. Accessed March 16, 2015.
  9. Widmer RJ, et al. The Mediterranean diet, its components and cardiovascular disease. Am J Med 2014;128:229-238.