Research Summary

Bilberry and grape seed extract may improve blood pressure.

Key finding

Intervention with bilberry and grape seed extract decreased systolic blood pressure by 4.7 mmHg (p < 0.001).

This study investigated the effects of long-term bilberry and grape seed extract supplementation on blood pressure in individuals at risk of type 2 diabetes mellitus (T2DM). It found significant reductions in systolic and diastolic blood pressure.

Evidence strength

Moderate confidence

Study type

RCTs

Follow-up

Medium-Term (3–12 mo)

Some Concerns bias

Last updated July 8, 2026

Quick read

Study at a glance

The essential study design details in one scan.

Population

Young Adult (19–39), Middle Aged (40-64), Male, Female, Asia-Pacific (APAC), with T2 Diabetes

Intervention

Bilberry and grape seed extract

Study type

RCTs

Follow-up

Medium-Term (3–12 mo)

Primary outcome

HbA1c

Comparator

Control extract

Plain-language summary

What this paper says

A plain-language read of the study's main message and where it applies.

Study focus

Clinical relevance

Managing blood pressure is crucial for individuals at risk of T2DM, as hypertension can lead to serious cardiovascular complications. The significant reductions in blood pressure observed in this study suggest that bilberry and grape seed extract may offer a natural dietary approach to improve cardiovascular health in this population, potentially reducing the risk of diabetes-related complications.

Keep in mind

The study did not assess long-term effects beyond the intervention period. Sample size and demographic diversity may limit generalizability. Lack of significant changes in other metabolic markers raises questions about broader efficacy.

Published in

Journal Reference

Publication details and source links for this paper.

Teresa G, Alan WW, Wendy RR, et al. Long-term supplementation with bilberry and grape seed extract can improve blood pressure in individuals at risk of T2DM. Frontiers in Nutrition. 2023;10:1139880. doi:10.3389/fnut.2023.1139880

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Main Effects

Systolic blood pressure decreased by 4.7 mmHg (p < 0.001).

Diastolic blood pressure decreased by 2.3 mmHg (p = 0.0009).

No significant effects on fasting HbA1c, fasting plasma glucose, or cholesterol levels.

Evidence network

How this study fits

Understand where this research contributes within the broader evidence network.

Evidence Context

This study contributes evidence to Bilberry extract and 2-hour plasma glucose, Advanced glycation end products (AGEs), Diastolic blood pressure, and 10 more.

This study contributes evidence to

Intervention

Bilberry extract

Outcome

2-hour plasma glucose

Evidence topic

Glycemic Control

Primary intervention

Bilberry extract

Primary outcomes

2-hour plasma glucose
Advanced glycation end products (AGEs)
Diastolic blood pressure

Evidence topics

Glycemic Control HbA1c Reduction

Primary intervention

Bilberry extract

Primary outcomes

2-hour plasma glucose Advanced glycation end products (AGEs)Diastolic blood pressure

Evidence relationships

Intervention and outcome relationships this study adds to the evidence network.

Evidence pairs

Relationships

Evidence topics

contributes_evidence

Editorial context

Why this study matters

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Evidence network role

This section describes how the study fits into the current evidence network. It does not determine whether an intervention works on its own.

Moderate contributionModerate confidenceNetwork score: 64

Why it is useful

Contributes to 13 evidence relationships
Includes primary outcome data
Linked to 2 direct semantic evidence topics

Topic contributions

Evidence topic

Contributes evidence

Evidence topic

Bilberry extract → Total cholesterol

Evidence profile

NoneNo ChangeMetabolic Health

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Evidence Suggest

Bilberry and grape seed extract reduced systolic blood pressure by 4.7 mmHg.
Diastolic blood pressure was lowered by 2.3 mmHg.
No significant impact on glucose or cholesterol levels was observed.

Who this applies to

Individuals at risk for type 2 diabetes mellitus.
Adults with elevated blood pressure.
Patients seeking dietary interventions for cardiovascular health.

Keep in Mind

Results may not apply to populations outside the study's demographic.
Further research is needed to confirm long-term benefits.
The study did not evaluate the effects of other lifestyle factors on outcomes.

Between the Lines

The study did not assess long-term effects beyond the intervention period.
Sample size and demographic diversity may limit generalizability.
Lack of significant changes in other metabolic markers raises questions about broader efficacy.

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Connected Evidence

Explore related studies, evidence collections, and research questions.

This study contributes to evidence on Bilberry extract and Blood Pressure, Bilberry extract and Blood Pressure.

Related evidence relationships

Explore in Evidence Archive

This study contributes to the evidence on the following intervention-outcome relationships.

Bilberry extractBlood Pressure

Supplements

1 studies

Detailed evidence

Bilberry extractBlood Pressure

Supplements

1 studies

Detailed evidence

Bilberry extractHbA1c

Supplements

2 studies

Detailed evidence

Included in these evidence collections

Curated evidence collections and hubs this study is part of.

HbA1c Evidence Hub

All studies measuring HbA1c

2 studies

outcome_hub

Measures HbA1c as a key outcome.

Bilberry extract Evidence Hub

All studies on Bilberry extract

1 studies

intervention_hub

Contributes to Bilberry extract evidence base.

Blood Pressure Evidence Hub

All studies measuring Blood Pressure

1 studies

outcome_hub

Measures Blood Pressure as a key outcome.

Does Bilberry extract improve diastolic blood pressure?

Emerging Evidence

Bilberry extract appears to improve Diastolic blood pressure.

ConsensusScore™: Consistency cannot yet be determined from the available evidence.

Ranked evidence signals

1
Diastolic blood pressure
EvidenceScore™ Emerging | EvidenceScore™ 51.7 | strong positive | ConsensusScore™ Unclear | 1 study

Why this answer: This answer is based on a single supporting study.

Limitations

Only one supporting study is available.
Consistency cannot yet be determined.
Population details are unavailable.

View Full Evidence

Does Bilberry extract improve systolic blood pressure?

Emerging Evidence

Bilberry extract appears to improve Systolic blood pressure.

ConsensusScore™: Consistency cannot yet be determined from the available evidence.

Ranked evidence signals

1
Systolic blood pressure
EvidenceScore™ Emerging | EvidenceScore™ 51.7 | strong positive | ConsensusScore™ Unclear | 1 study

Why this answer: This answer is based on a single supporting study.

Limitations

Only one supporting study is available.
Consistency cannot yet be determined.
Population details are unavailable.

View Full Evidence

Does Bilberry extract improve HbA1c?

Emerging Evidence

Bilberry extract may improve HbA1c.

ConsensusScore™: Results are mixed and should be interpreted cautiously.

Evidence caveat: The available evidence reports mixed findings.

Ranked evidence signals

1
HbA1c
EvidenceScore™ Emerging | EvidenceScore™ 46.9 | moderate positive | ConsensusScore™ Mixed | 1 study

Why this answer: This answer is cautious because the available studies report mixed findings.

Limitations

Only one supporting study is available.
Population details are unavailable.

View Full Evidence

Does Bilberry extract improve 2-hour plasma glucose?

Limited Evidence

Current evidence does not show a clear benefit of Bilberry extract for 2-hour plasma glucose.

ConsensusScore™: Consistency cannot yet be determined from the available evidence.

Ranked evidence signals

1
2-hour plasma glucose
EvidenceScore™ Limited | EvidenceScore™ 34.2 | neutral | ConsensusScore™ Unclear | 1 study

Why this answer: This answer is based on a single supporting study.

Limitations

Only one supporting study is available.
Consistency cannot yet be determined.
Population details are unavailable.

View Full Evidence

How connections are generated

Next steps

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Evidence topics

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Glycemic Control Evidence Hub HbA1c Reduction Evidence Hub

Explore in archive

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All studies on Bilberry extract and Diastolic blood pressure All studies on Bilberry extract and Systolic blood pressure All studies on Bilberry extract and HbA1c All studies on Bilberry extract and 2-hour plasma glucose

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