Blackcurrant and Blood Flow: What Human Studies Measure Before You Buy
You pause on a supplement page and see a phrase such as supports circulation. It sounds useful, but what would a researcher actually need to measure before that phrase meant anything?
Blood flow is not one universal number. A study might record blood pressure, the amount of blood pumped by the heart, resistance in the blood vessels, the width of one artery, flow through one limb, or oxygen patterns inside a working muscle.
Direct answer: Human blackcurrant blood flow studies measure different endpoints and do not all reach the same conclusion. Some small trials reported changes in specific cardiovascular or peripheral-circulation measures, while other trials found no meaningful effect under different protocols. A result from one extract, population, serving plan or exercise task cannot automatically be applied to every blackcurrant supplement.
One Phrase, Seven Different Endpoints
These measures sit in the same cardiovascular system, but they answer different questions. A change in one does not automatically prove better cardiovascular health, better circulation everywhere, or a clinical benefit.
| Endpoint | What it tells researchers | How it may be measured | What it does not prove |
|---|---|---|---|
| Systolic and diastolic blood pressure | Pressure in the arteries as the heart contracts and relaxes | An automated cuff or validated blood-pressure monitor | How much blood reaches every tissue, or whether disease risk has changed |
| Heart rate | How often the heart beats each minute | Electrocardiography, pulse monitoring or a heart-rate sensor | The volume pumped with each beat or blood flow to a particular limb |
| Cardiac output | The total volume of blood pumped by the heart each minute | Non-invasive haemodynamic monitoring or other validated methods | That a specific artery widened or a muscle received more oxygen |
| Stroke volume | The amount of blood pumped with each heartbeat | Derived from cardiovascular monitoring | A treatment effect or improved circulation throughout the body |
| Total peripheral resistance or systemic vascular resistance | The overall resistance the heart pumps against in the systemic circulation | Calculated from blood pressure and cardiac output data | Why resistance changed, or that every person will respond similarly |
| Artery diameter or regional limb blood flow | What happened in a named vessel or body region | Ultrasound, Doppler methods or flow calculations | Improved circulation everywhere or a lasting health outcome |
| Tissue oxygenation | Changes in oxygenated and deoxygenated blood signals within a local tissue | Near-infrared spectroscopy | Whole-body blood flow, brain function or disease prevention |
Four Studies, Four Different Questions
The useful question is not simply whether blackcurrant was studied. We need to ask who took it, what form they took, how long they took it, what task they performed and which endpoint was measured.
A. Resting cardiovascular function in trained male cyclists
- Population: 15 endurance-trained male cyclists
- Product or ingredient form: A specific New Zealand blackcurrant extract used in the research
- Serving duration: Seven-day protocols using different doses
- Test context: Supine rest
- Endpoints: Blood pressure, heart rate, cardiac output, stroke volume and total peripheral resistance
- Result direction: The 2017 trial reported dose-related changes in some haemodynamic measures, while blood pressure and heart rate were unchanged
- Main limitation: A very small group of trained men at rest does not represent the wider New Zealand population
B. Forearm circulation during typing work
- Population: A small human crossover sample
- Product or ingredient form: Blackcurrant anthocyanin intake
- Serving duration: Intake assessed within a controlled crossover protocol rather than a long-term daily-use trial
- Test context: Repetitive typing work
- Endpoints: Forearm blood flow and muscle oxygenation assessed with near-infrared spectroscopy
- Result direction: The 2005 study reported a change in forearm blood flow, but no significant difference in muscle oxygen consumption
- Main limitation: Forearm circulation during one controlled task is not the same as whole-body circulation
C. Low-intensity intermittent contractions in healthy men
- Population: 15 healthy men
- Product or ingredient form: A defined New Zealand blackcurrant extract
- Serving duration: A study-specific supplementation protocol before testing
- Test context: Low-intensity sustained intermittent isometric contractions
- Endpoints: Blood pressure, heart rate, cardiac output, stroke volume, total peripheral resistance, femoral artery diameter and muscle outcomes
- Result direction: The study, published online in 2025 and issued in 2026, found no effect under this protocol
- Main limitation: The result applies to a narrow contraction task in a small male sample, not every exercise setting or daily-life situation
D. Rest and walking responses in young Southeast Asian women
- Population: 16 young adult Southeast Asian women
- Product or ingredient form: A defined New Zealand blackcurrant extract
- Serving duration: A randomised crossover study protocol
- Test context: Rest and walking
- Endpoints: Cardiorespiratory, cardiovascular and metabolic responses
- Result direction: The 2026 study found no consistent effect across the cohort, although some participants showed reduced systemic vascular resistance
- Main limitation: A responder pattern in a small study cannot predict whether any individual shopper will respond
A separate 2017 trial also examined femoral artery diameter during a sustained isometric contraction and reported changes under that particular task. Read it alongside the newer null study, not as a universal verdict. For the separate training and recovery question, see our blackcurrant extract muscle recovery guide.
Measured, Associated or Merely Inferred?
| Directly measured in a study | Reasonable but limited interpretation | Unsupported leap |
|---|---|---|
| Blood pressure was unchanged in a small resting trial | That protocol did not alter blood pressure in that sample | Treats high blood pressure |
| Forearm blood flow changed during a typing task | A local peripheral-circulation measure changed in that test | Improves circulation everywhere |
| Femoral artery diameter was measured during contraction | The vessel response can be discussed within that exercise protocol | Prevents cardiovascular disease |
| Muscle oxygenation was measured locally | The study informs local muscle oxygen signals in that task | Improves brain function |
| Some participants showed a different vascular-resistance response | Responder variation may deserve further research | Works for everyone |
| A named research extract was tested | The finding belongs first to that product and protocol | Proves the Kiwi Superfoods product has the same effect |
Why Blackcurrant Studies Can Disagree
Different results do not make the research useless. They narrow the conclusion. Think of each trial as a map with boundaries.
- People: Population, sex, training status, baseline health and sample size can change the starting point and the chance of detecting an effect.
- Ingredient: Berry species and source, berry part, extract method, standardisation and anthocyanin disclosure determine what was actually tested.
- Protocol: Serving amount, intervention length, timing, rest versus exercise and the exact task can change the response.
- Measurement: Blood pressure, resistance, artery diameter, limb flow and tissue oxygenation are different endpoints measured with different tools.
- Analysis: A cohort average may look neutral even when some participants respond differently. Responder analysis is interesting, but it needs cautious confirmation.
- Study support: Funding and supplied products should be disclosed and considered alongside design quality, not treated as automatic proof for or against a result.
The balanced conclusion is specific: some small trials reported changes in selected endpoints, and other small trials found no effect in different populations or tasks. Results vary.
Before a Blood-Flow Result Reaches This Bottle
Research transfer needs checkpoints. Our NZ-grown blackcurrant skin extract capsules are a finished product, not the research preparation used in every published trial.
- Species: Was the study on Ribes nigrum?
- Berry part and form: Was it whole fruit, juice, powder, skin extract or another extract?
- Active disclosure: Was the anthocyanin amount clearly declared?
- Serving match: Was the serving amount and duration similar to the product being considered?
- People and context: Was the population and test task relevant to the shopper's question?
- Endpoint match: Did the study directly measure the outcome being claimed?
- Label fit: Does the current Kiwi Superfoods label provide enough information for a cautious comparison?
What we can say from the current product page is that the product is positioned as NZ-grown blackcurrant skin extract, supplied in capsules, includes vitamin C, and directs adults to take two capsules daily with or without food.
What we should not do is force a trial-to-bottle match. The live page currently uses inconsistent wording about whether the stated blackcurrant extract and vitamin C quantities apply per daily dose or per capsule. Until the current physical label or an approved product specification is checked, exact milligram amounts should not be used. An exact anthocyanin dose should not be assumed, and the product should not be presented as equivalent to CurraNZ or another research preparation.
What This Means Before You Buy
Use a narrow evidence-fit check rather than a broad benefits list:
- Confirm the ingredient identity and berry part.
- Look for declared extract and anthocyanin information.
- Read the serving directions.
- Check whether the cited research used the same form.
- Ask whether the claimed outcome was directly measured.
- Review warnings and personal suitability.
For a broader berry comparison and help translating label units, use our anthocyanin supplement and label-reading guide.
Safety Handoff
Readers who are pregnant or breastfeeding, use prescription medicines, take warfarin or other medicines that affect clotting, have a bleeding disorder, take phenothiazines, have surgery planned, have allergies or have persistent symptoms should seek qualified advice. Do not adjust medicines based on supplement information. See the full blackcurrant supplement safety guide.
General food-supplement education only. This article is not medical advice and does not diagnose, treat or prevent any condition.
Next Steps
Before accepting a circulation claim, look for three things: the endpoint that was measured, the people who were studied, and the match between the research product and the bottle you are considering. That keeps a promising result in its proper lane and makes a null result useful too.
Frequently Asked Questions
Does blackcurrant improve blood flow?
Some small human studies reported changes in specific blood-flow-related measures, while others found no effect under different protocols. The evidence does not support saying that blackcurrant improves blood flow for everyone.
What do human blackcurrant blood-flow studies actually measure?
They may measure blood pressure, heart rate, cardiac output, stroke volume, total peripheral resistance, artery diameter, regional limb blood flow or local tissue oxygenation. These endpoints are related but not interchangeable.
Is blood flow the same as blood pressure?
No. Blood pressure describes pressure in the arteries. Blood flow describes movement of blood through the heart, vessels or a named body region. One can change without proving the same change in the other.
Does a larger artery diameter mean better circulation?
Not automatically. A larger diameter in one artery during one controlled task is a local measurement. It does not prove better circulation throughout the body or a lasting clinical benefit.
What is total peripheral resistance?
Total peripheral resistance, also called systemic vascular resistance, is an estimate of the overall resistance the heart pumps against in the systemic circulation. It is usually calculated from blood pressure and cardiac output data.
Why do blackcurrant studies show different results?
Studies can differ in population, sex, training status, baseline health, sample size, extract, berry part, anthocyanin disclosure, serving plan, test task, endpoint, measurement tool and analysis method.
Do results from one blackcurrant extract apply to every supplement?
No. A finding belongs first to the exact extract, serving protocol, population and test used in that trial. It should not be transferred to another supplement without checking ingredient and protocol similarity.
What should I check before buying a blackcurrant extract?
Check the species, berry part, extract form, declared anthocyanin information, daily serving, match to cited research, directly measured outcome, warnings and personal suitability.
References
- Cook MD et al. Cardiovascular function during supine rest in endurance-trained males with New Zealand blackcurrant: a dose-response study. European Journal of Applied Physiology. 2017. https://doi.org/10.1007/s00421-016-3512-x
- Matsumoto H et al. Effects of blackcurrant anthocyanin intake on peripheral muscle circulation during typing work in humans. European Journal of Applied Physiology. 2005. https://doi.org/10.1007/s00421-004-1279-y
- Cook MD et al. Blackcurrant Alters Physiological Responses and Femoral Artery Diameter during Sustained Isometric Contraction. Nutrients. 2017. https://doi.org/10.3390/nu9060556
- Montanari S et al. New Zealand blackcurrant extract has no effect on physiological and cardiovascular responses during low-intensity sustained intermittent isometric contractions in men. European Journal of Applied Physiology. Published online 2025, issue 2026. https://doi.org/10.1007/s00421-025-05971-3
- Willems MET et al. Effect of New Zealand blackcurrant extract on rest and walking-induced cardiorespiratory and metabolic responses in young adult Southeast Asian women. European Journal of Applied Physiology. 2026. https://doi.org/10.1007/s00421-026-06215-8
