When the Heat Keeps Coming: New Research Explores CurraNZ and Recovery from Repeated Heat Stress

A new study presented at the American Physiology Summit 2025 has put New Zealand blackcurrant extract to the test in some of the most extreme heat conditions ever used in supplement research – shedding light on a question that matters deeply to athletes, military personnel, and anyone who trains or competes in punishing heat: can blackcurrant supplementation help the body cope better when the heat just keeps coming?

The Study at a Glance

Researchers at the University of Connecticut’s Korey Stringer Institute – one of the world’s leading centres for exertional heat illness research, funded by the US Department of Defence – enrolled nine participants in a rigorous crossover trial. Each participant completed two full conditions: five days of heat acclimation (HA) with 784 mg of blackcurrant per day (equivalent to just over 3 capsules of CurraNZ), and five days with no supplement as a control.

The conditions were uncompromisingly harsh. Training and testing sessions were conducted at approximately 40°C ambient temperature with 40% relative humidity – an environment that translates to a perceived heat load of around 42°C effective temperature. Think desert-climate military deployment or a mid-summer training camp in Southeast Asia. 

Two heat tolerance tests (HTTs) framed the acclimation period. The first – HTT1 – was a 120-minute steady-state walk at low intensity. The second – HTT2 – was a run at 65% of maximum aerobic capacity, continued until core (rectal) temperature reached 39.5°C. The sequence matters: HTT1 came first, HTT2 second.

What the Study Found – and What It Didn’t

To be clear about the primary result: blackcurrant supplementation did not significantly alter core temperature, heart rate, sweat loss, or time-to-temperature during either heat tolerance test compared to control. Heat acclimation itself – regardless of supplement – was the dominant driver of physiological adaptation, as one would expect.

That is an important, honest finding. CurraNZ does not function as a cooling agent at these temperatures, and this study does not claim otherwise. 

What the study did reveal, however, is more nuanced – and arguably more interesting for practical athletic contexts.

The Recovery Signal: Between-Test Resilience

After completing HTT1 (the long, low-intensity exposure), participants in the blackcurrant condition showed greater improvements in thermal tolerance at HTT2 compared to those in the control condition. In plain terms: individuals who had been taking New Zealand blackcurrant extract appeared to recover more effectively from the first heat stress challenge, arriving at the second test in a better physiological position.

This is not a thermoregulatory effect during exercise – it is a recovery and resilience effect between heat exposures. The distinction is significant. For athletes training twice daily in the heat, competing across multiple days of a tournament, or military personnel repeating physically demanding work shifts in extreme environments, the ability to bounce back between exposures could carry real performance and safety implications.

The researchers noted considerable inter-individual variability in response, underscoring the relevance of personalised nutrition strategies in the heat. Not every individual responded identically – which is consistent with the broader pattern seen across blackcurrant research.

Researcher’s view: ‘Blackcurrant may offer an additional layer of support for recovery between heat exposures’

Gabrielle Brewer (pictured above), PhD and the Associate Director at the Korey Stringer Institute at UNF who led the study, observed: 

“Our blood biomarker data showed that blackcurrant supplementation significantly increased antioxidant activity before the first heat exposure, which provides a strong rationale for continuing this work in a larger sample. 

“These findings do not suggest that blackcurrant is a ‘magic bullet,’ but they do point to possible mechanisms that may help explain recovery or metabolic benefits in some individuals,  particularly those with lower habitual antioxidant intake or greater oxidative stress.

“There is no magic supplement that can outperform training adaptations, and heat acclimation remains the foundation. But blackcurrant may offer an additional layer of support for recovery between heat exposures, especially for certain individuals (i.e., older women) or under added stressors (i.e., travel, repeated training days, or injury)”.

Part of a Growing Picture

This study does not stand alone. CurraNZ has now been investigated across multiple heat stress contexts, and a coherent adaptive profile is beginning to emerge.

In 2024, Dr Ben Lee and colleagues published work in the European Journal of Applied Physiology showing that our New Zealand blackcurrant extract modulates heat shock protein responses during exertional heat stress – specifically elevating these cytoprotective proteins at baseline – these are positively associated with cellular stress defences. Heat shock proteins are the body’s internal distress signal and repair system; the fact that blackcurrant influences this pathway suggests a mechanism that may partly explain the recovery observations seen in this newer work.

In 2025, another paper that stemmed from this project, published in Research in Sports Medicine, found that CurraNZ dramatically reduced gastrointestinal symptoms during running in the heat – from a 92% incidence in the control group down to just 25%. Gut integrity under thermal stress is a significant and often overlooked issue for endurance athletes.

And in 2020,  another paper (Journal of Science and Medicine in Sport) demonstrated that CurraNZ enhanced fat oxidation during 60 minutes of running in 34°C heat, without altering thermoregulatory variables – pointing to a metabolic efficiency effect under heat load.

Taken together, these findings describe a supplement that operates across several layers of physiological stress response: cellular protection, gut integrity, metabolic efficiency, and now – potentially – inter-exposure recovery. 

A Practical Takeaway for Athletes and Active Individuals

This study, conducted under US Department of Defence-funded conditions at a leading heat illness research institute, adds a meaningful piece to an evolving scientific story. The headline is that repeated exposure to extreme heat may be better tolerated with New Zealand blackcurrant extract in the recovery window between efforts, and that the underlying biological mechanisms for this are becoming clearer.

For athletes facing multi-day competition in hot climates, coaches planning double-session heat-training blocks, or anyone exposed to repeated occupational heat stress, this emerging recovery angle deserves attention – and further investigation.

The research is at an early stage, and the study’s small sample size warrants a cautious interpretation. But the direction of evidence is consistent, and the mechanistic rationale is credible.

The Science Behind the Berry

CurraNZ is standardised to the anthocyanin compounds present in high concentrations in specific New Zealand blackcurrant cultivars – principally delphinidin 3-rutinoside and cyanidin 3-rutinoside. These compounds enhance blood flow and vascular responsiveness, are present at notably high concentrations in the varieties we use of New Zealand-grown blackcurrants. 

The anthocyanin profile is not incidental to the heat stress findings. Multiple mechanisms have been proposed, including effects on nitric oxide bioavailability, microvascular perfusion, and cellular stress signalling – all of which intersect with how the body manages and recovers from thermal challenges.

Study Reference

Brewer GJ et al. “The Effects of Blackcurrant Supplementation on Physiological Responses to Repeated Exercise-Heat Exposures.” Physiology (American Physiology Summit 2025), May 2025.

DOI: 10.1152/physiol.2025.40.S1.1617

Funded by the US Department of Defense (DoD BA20029). Study conducted at the Korey Stringer Institute, University of Connecticut.