First, what BDNF is. Brain-derived neurotrophic factor is a small protein the nervous system makes to keep its own wiring in good repair. It helps neurons survive, supports the growth of new connections between them, and strengthens connections that already exist. It is especially busy in the hippocampus, the seahorse-shaped structure most involved in learning and memory. Nobody eats BDNF and nobody sells it in a bottle: the body produces it, levels shift with age, sleep, stress and activity, and low levels turn up alongside depression and cognitive decline in observational work. That is why it keeps appearing in exercise research. It is the closest thing available to a measurable marker of "the brain is being maintained."
What was measured, and where. One caveat has to come early, because it shapes everything below. Nobody can sample a living human brain, so studies measure BDNF in blood, either serum or plasma. Circulating BDNF is a proxy. A large share of what sits in serum comes from platelets rather than neurons, and how tightly the blood number tracks anything inside the skull remains an open question. Every finding here describes the blood marker.
The study. Daniel Moreau and B.T. Chapple-De Lange at the University of Auckland pooled the evidence on what a single session of cardiovascular exercise does to three growth factors in healthy adults: BDNF, vascular endothelial growth factor (VEGF) and insulin-like growth factor-1 (IGF-1). They searched seven databases plus gray literature, and two reviewers independently handled study selection, data extraction and risk-of-bias assessment. Twenty-two studies with 628 participants met the criteria; only the subset reporting usable pre- and post-exercise BDNF values went into the statistical pooling. It was published in Brain Research in June 2026.
The result, with the actual number. Acute exercise raised circulating BDNF by a pooled Hedges' g of 0.48, 95% CI [0.29, 0.68], p < 0.001. Hedges' g is an effect size: it expresses change in standard deviations rather than in units of the marker, which is what lets studies using different lab assays be compared at all. As a rough reading, 0.2 counts as small, 0.5 as moderate, 0.8 as large. So 0.48 is a genuinely moderate effect, and the confidence interval sits well clear of zero, meaning the direction is solid even though the exact size is not pinned down. Effects ran directionally larger after higher-intensity sessions and in younger adults.
Transient means transient. The rise showed up most clearly with moderate-to-vigorous intensity and when blood was drawn immediately after the session. Sampling timing was one of the moderators the authors flagged, which is another way of saying the signal fades. This is an acute response to one workout, not evidence of a permanently higher baseline. Whether repeated sessions shift the resting level over months is a separate question, and this review does not answer it.
VEGF and IGF-1 went nowhere. Evidence for the other two factors was limited, inconsistent, and too sparse to pool. The authors rated overall confidence in the evidence as moderate for BDNF and low for VEGF and IGF-1, a judgment worth repeating, because coverage of this field tends to lump all three together as "exercise grows your brain."
Who was studied, and doing what. Here the review is thinner than it should be. The 628 participants are described only as healthy adults: no sex breakdown, no age range, no mean age. Ages clearly varied, since the authors report larger effects in younger adults, but they never say what "younger" means. The type of cardio is left equally vague. "A single bout of cardiovascular exercise" covers a lot of ground, and the review does not name the modalities, though the requirement for blood drawn immediately afterwards means most of this work is done on a stationary bike or a treadmill in a lab rather than on a trail. Session length is not reported either. So the effect size is real, but which people it applies to, and after exactly what kind of workout, are questions the paper leaves open.
What this does not show. No cognitive outcome was measured. Nobody in these 22 studies got demonstrably better at remembering, concentrating or learning; what changed was a protein concentration in a blood sample. The step from "BDNF went up for a while" to "thinking improved" is exactly the one this literature has not yet built. The honest summary is mechanistic support for something already believed on other grounds, that regular cardiovascular exercise is good for the aging brain, rather than a fresh reason to believe it.
Practical reading. Do not train for a blood marker. If brain health is part of why you exercise, the useful signal here is that intensity was the lever that moved the number most: moderate-to-vigorous work, the kind where holding a conversation gets awkward, rather than a gentle stroll. That advice would stand without any BDNF data at all, which is rather the point. Treat the protein as an explanation for why exercise plausibly helps, not as the thing being chased.
Bottom line. A single cardio session produces a moderate, short-lived rise in circulating BDNF, on moderate-quality evidence from 22 studies and 628 people. The two related growth factors show nothing reliable. It is a mechanism finding, and a reasonable one, but it changes nothing about what a sensible exercise week looks like.
Medical note. This article is intended for general educational purposes and is not a substitute for professional medical advice.