Serum and plasma brain-derived neurotrophic factor concentration are elevated by systemic but not local passive heating.
Level 2 - randomized trial
Controlled crossover experimental trial in humans
PubMed 34882699 · doi:10.1371/journal.pone.0260775
What was done
Ten recreationally active males completed three 90-minute experimental conditions using a water-perfused suit: whole-body heating (WBH), lower-body heating with upper-body cooling (LBH), and a control condition (CON). Blood was sampled before, immediately after, and 1 hour post-heating to evaluate serum and plasma brain-derived neurotrophic factor (BDNF) concentrations, platelet counts, and BDNF release per platelet. Rectal temperature, cardiac output, and femoral artery shear rate were measured throughout each protocol.
What was found
Circulating BDNF increased following WBH (serum: 19.1 ± 5.0 to 25.9 ± 11.3 ng/ml; plasma: 2.74 ± 0.9 to 4.58 ± 2.0 ng/ml; p < 0.044) relative to CON (serum: 18.6 ± 6.4 to 16.8 ± 3.4 ng/ml; plasma: 2.49 ± 0.69 to 2.82 ± 0.89 ng/ml). In contrast, LBH did not significantly alter BDNF levels (serum: 19.1 ± 4.7 to 22.3 ± 4.8 ng/ml; plasma: 3.25 ± 1.13 to 3.39 ± 0.90 ng/ml; p > 0.126). Platelet counts rose post-heating (p < 0.001), but BDNF content per platelet was unchanged across conditions (p = 0.392). Physiological markers (rectal temperature, cardiac output, shear rate) increased significantly more during WBH than LBH (p < 0.001).
Why it matters
This study indicates that elevating circulating BDNF via passive heat exposure requires systemic thermal and cardiovascular strain rather than localized tissue heating.
Limits
The sample size was very small (n = 10) and exclusively comprised young, recreationally active men. Only acute responses up to 1 hour post-heating were tracked, precluding conclusions about chronic adaptations or clinical populations.
Cited by
- supports Sitting in a 104°F hot bath with shoulders submerged for 20 minutes increases brain-derived neurotrophic factor (BDNF).