Does Creatine Improve Your Cardio Fitness? What the Evidence Says

Creatine is one of the most studied supplements in sports science, and this year it moved beyond the weight room: a new randomized trial found it improved cognitive markers in adults over 45. What it has not been shown to do is raise VO2max. Here is what the evidence actually supports, and where it stops.

Why is creatine suddenly part of the cardio conversation?

Creatine monohydrate has a 30-year track record in strength and power sports, where it reliably improves performance in short, high-intensity efforts by helping muscle regenerate ATP faster during the first seconds of maximal work. That reputation has recently spilled into cardio and longevity discussions, driven by a wave of 2025-2026 research on creatine and aging. A widely shared systematic trial out of Texas A&M this year tested creatine in sedentary adults aged 45 to 65 and found it improved lean mass, strength, and several markers of cognitive function over 12 weeks, with or without an accompanying exercise program (Chun et al., 2026). Read quickly, a headline like that can sound like creatine is a general fitness enhancer. The more precise claim is narrower, and it matters which parts of "cardio fitness" creatine actually touches.

Does creatine improve VO2max or endurance performance?

The most direct answer comes from a systematic review and meta-analysis of 13 controlled trials in trained athletes, published in Sports Medicine. Pooling the results, creatine monohydrate supplementation produced a statistically non-significant, trivial negative effect on endurance performance (standardized mean difference -0.07, 95% CI -0.32 to 0.18, p = 0.47), and the result held after the authors excluded studies with signs of publication bias (Fernández-Landa et al., 2023). Their conclusion is direct: creatine monohydrate supplementation was shown to be ineffective on endurance performance in a trained population. That is a meaningful null result. Creatine adds roughly 1-2% to body mass through water retention in muscle, which is a real cost for anyone doing sustained aerobic work and carrying their own body weight, and the review found no offsetting aerobic benefit to compensate for it.

This tracks with what is known about creatine's mechanism. It buffers phosphocreatine stores, which regenerate ATP anaerobically for efforts lasting roughly 10 seconds. VO2max is a measure of how much oxygen your heart, lungs, and muscles can take up and use during sustained hard effort, an aerobic system that runs on a completely different energy pathway. There is no biologically plausible route from more phosphocreatine to a higher aerobic ceiling, and the trial evidence agrees: nothing in the literature to date shows creatine raising VO2max in trained or untrained adults.

So what did the 2026 aging trial actually find?

The Texas A&M trial randomized 64 healthy but sedentary adults aged 45-65 (40 women, 24 men) to creatine or a maltodextrin placebo for 12 weeks, with participants choosing whether to also follow an exercise-and-diet program. Creatine supplementation without any exercise intervention still increased lean tissue mass, strength, and muscular endurance, and produced favorable shifts in some blood lipids, HbA1c, and cognitive test scores. Adding a structured exercise and weight-loss program on top of creatine improved those same outcomes further, including a greater drop in body fat percentage (Chun et al., 2026). The authors are careful to flag that the individual cognitive and biomarker findings should be read as exploratory, and the study's lead author chairs a scientific advisory board for a creatine manufacturer, a conflict of interest worth knowing about a positive result.

Every outcome that improved in that trial is downstream of muscle: lean mass, strength, muscular endurance, body composition. None of it is a measure of cardiorespiratory fitness. That distinction is the whole story. Creatine appears to help older adults keep and build muscle, which is a genuinely valuable outcome tied to healthy aging, independent of whether it does anything for your heart and lungs.

What is the muscle-brain axis, and is it relevant here?

Two 2025 papers in Frontiers in Nutrition proposed a mechanism for creatine's reported cognitive effects: a "muscle-brain axis," where creatine's role as an energy buffer in both tissues, combined with exercise-induced myokines like brain-derived neurotrophic factor (BDNF), may support neuroplasticity alongside muscle maintenance (Ribeiro et al., 2025). A companion review focused on aging populations found creatine plus resistance training brought modest gains in memory, processing speed, and executive function, largely in people with lower baseline creatine levels, while cautioning that dosing protocols still need larger trials to confirm (Li, 2026). Both papers call this a proposed mechanism, not an established fact, and several of the researchers across this literature disclose financial ties to creatine manufacturers, which does not invalidate the findings but is worth weighing against any single positive result.

Does creatine work the same way for everyone?

No, and the clearest documented difference is by sex. Females have 70-80% lower endogenous creatine stores than males on average, tied to estrogen's role in creatine kinetics, which means the case for supplementation may be stronger for women, not weaker. A lifespan review found pre-menopausal women see reliable strength and performance benefits, while post-menopausal women may see gains in skeletal muscle size and function at higher doses (0.3 g per kg of body weight per day) combined with resistance training, plus favorable effects on bone density (Smith-Ryan et al., 2021). Vegetarians and vegans, who get little dietary creatine, tend to see the most dramatic muscle-level changes; habitual meat-eaters with already-high stores see less.

Is creatine safe, and does it affect the kidneys?

This is the most common safety question, and a 2026 systematic review and meta-analysis of 19 randomized controlled trials gives the most current answer. Creatine supplementation was associated with a small but measurable rise in serum creatinine (mean difference 0.13 mg/dL), a lab marker that is often mistaken for kidney damage. But the same analysis found no difference in blood urea or in estimated glomerular filtration rate (eGFR), the more direct marker of how well the kidneys are actually filtering, and no difference between supplementation periods under and over one month (Tsiaras et al., 2026). The honest reading is that creatine raises a lab value that looks concerning in isolation without producing a change in actual kidney function, at least across the RCTs available. The authors note that trials extending past one year are still needed before the long-term picture is fully settled, and anyone with pre-existing kidney disease should talk to a physician before starting creatine rather than relying on population-level trial data.

Where does creatine actually fit next to REHIT?

CAROL's own protocol, Reduced Exertion High-Intensity Interval Training (REHIT), is built specifically to raise VO2max through short, near-maximal sprints, the training stimulus the evidence says actually moves that number. Creatine is not a substitute for that stimulus, and nothing in the literature suggests taking it will make your cardio sessions more effective at raising aerobic capacity. What it may reasonably add is support for the muscle mass and strength that matter alongside cardio for healthy aging, particularly past 45, where preserving lean tissue becomes its own priority independent of heart and lung fitness. The two are complementary claims, not competing ones: train for VO2max, and consider creatine, separately, for muscle.

The bottom line

Creatine's evidence base is large and mostly consistent on one point: it does not improve endurance performance or VO2max, and a body-mass cost from water retention makes it a plausible net negative for pure aerobic pursuits. What it has real trial support for, including in a 2026 randomized trial in adults 45-65, is helping preserve and build muscle, strength, and possibly some cognitive function, benefits that stand on their own merits for healthy aging. The muscle-brain axis mechanism proposed to explain the cognitive findings is still an early hypothesis, several of the researchers behind this literature have financial ties to creatine manufacturers, and kidney-safety data beyond one year is still thin. If your goal is a higher VO2max, the evidence points to structured cardio training, not a supplement. If your goal is preserving muscle as you age, creatine has a real case behind it. This article is not medical advice; talk to a physician before starting creatine if you have kidney disease or another condition that affects how you process it.