BDNF: What It Does, What Raises It and What Your Levels Mean
Brain-derived neurotrophic factor (BDNF) is a protein that supports the survival, growth, and differentiation of neurons and synapses - the physical infrastructure of learning, memory, and cognitive function. BDNF declines with aging, sedentary lifestyle, poor sleep, and chronic stress. Exercise is the best-supported way to raise it in people; much of the rest of the evidence comes from animal studies.
- BDNF binds the TrkB receptor on neurons and promotes: neurogenesis (the production of new neurons, primarily in the hippocampal dentate gyrus), synaptic plasticity (long-term potentiation, the cellular mechanism of learning and memory), dendritic branching, and neuronal survival under stress. Low BDNF is consistently associated with depression, cognitive decline, and elevated Alzheimer's risk.
- Aerobic exercise is the most potent known activator of BDNF in humans. In a meta-analysis, a single session of exercise raised BDNF with a moderate effect, and regular training strengthened that response.3 Regular aerobic exercise training produces sustained BDNF elevation and measurable increases in hippocampal volume - the brain region most affected by Alzheimer's disease.
- Sleep is essential for BDNF protein synthesis and consolidation. Sleep deprivation acutely reduces BDNF levels. The growth hormone secreted during slow-wave sleep drives BDNF transcription, making slow-wave sleep quality directly relevant to BDNF status. Chronic sleep restriction produces progressive BDNF depletion.
- Claims that particular foods or nutrients, such as omega-3 fats, curcumin, flavonoids or fasting, raise BDNF rest mainly on animal and small short-term studies; none has been shown to raise BDNF in the human brain.
- BDNF cannot be effectively supplemented directly - the protein does not cross the blood-brain barrier, and systemic BDNF injections produce adverse effects. The strategy is to upregulate endogenous BDNF production through lifestyle: exercise first, sleep second, dietary polyphenols and omega-3 third.
Brain-derived neurotrophic factor was discovered in 1982 by Yves-Alain Barde and Hans Thoenen at the Max Planck Institute. Its name captures its essential function: it is a factor derived from brain tissue that promotes the growth and survival of neurons. What was not initially appreciated was that BDNF would emerge as one of the most important molecules in the biology of cognitive aging - a protein whose levels in the brain are directly shaped by lifestyle choices and whose decline is mechanistically connected to depression, cognitive deterioration, and Alzheimer's disease.1
What BDNF Does in the Brain
BDNF binds the high-affinity tropomyosin receptor kinase B (TrkB) receptor on neurons. This binding initiates intracellular signaling cascades - primarily through PI3K/Akt/mTOR and MAPK/ERK pathways - that promote neuronal survival (anti-apoptotic signaling), synaptic strengthening (by facilitating long-term potentiation, the cellular mechanism of memory formation), dendritic arbor expansion (increasing the surface area for synaptic connections), and neurogenesis in the hippocampal subgranular zone.2
The hippocampus is the brain region most dependent on ongoing BDNF signaling for its function and structural maintenance. It is also the region first and most severely damaged in Alzheimer's disease - and the region where exercise-induced neurogenesis and BDNF-driven structural plasticity are most readily demonstrated in human neuroimaging studies. Whether raising BDNF protects people against Alzheimer's disease has not been shown in trials.
What "BDNF levels" means, and can you test yours?
Can you test your BDNF level?
BDNF can be measured in blood, but the number depends heavily on how the sample is handled. In a study of blood drawn from healthy men, serum BDNF rose sharply during the first hour of clotting, and serum and plasma values did not correlate with each other: the authors concluded that serum and plasma measure two different pools of BDNF.6 Whether blood levels reflect the brain is known only from animals: blood BDNF correlated moderately with BDNF in the hippocampus in rats and pigs (r² about 0.4).7 A single result from a commercial test is therefore hard to interpret.
The best-studied link is with depression. A meta-analysis found lower serum BDNF in 2,384 depressed people not taking antidepressants than in 2,982 healthy controls (effect size d = -0.71), but the gap shrank substantially once publication bias was accounted for (d = -0.47), and BDNF did not track how severe the depression was. The authors concluded the evidence was slimmer than first thought.8 For an individual, the more useful measures are the behaviors that raise BDNF, above all regular aerobic exercise, rather than the BDNF number itself.
Aerobic Exercise: The Most Potent BDNF Activator
The relationship between aerobic exercise and BDNF is one of the most robustly established in neuroscience. In a meta-analysis of 29 studies with 1,111 participants, a single session of exercise raised BDNF with a moderate effect, and regular training made each session's rise larger; effects were smaller in studies with more women.3 Regular exercise produced only a small rise in resting BDNF levels that supports ongoing neuroplasticity.3
The landmark human neuroimaging study by Erickson et al. (PNAS, 2011) randomized 120 sedentary older adults to aerobic walking (3x per week, 40 min sessions) or stretching control for 12 months. The aerobic exercise group showed significant increases in hippocampal volume (by approximately 2 percent - reversing approximately 1 to 2 years of normal age-related hippocampal shrinkage), higher serum BDNF, and improved spatial memory. In the stretching control group, hippocampal volume continued to decline.4
Sleep and BDNF: The Slow-Wave Connection
BDNF protein synthesis in neurons is regulated by the same molecular machinery that mediates synaptic plasticity during sleep. During slow-wave sleep, the synaptic homeostasis hypothesis proposes that neurons consolidate learning from the preceding waking period by strengthening high-importance synapses and weakening low-importance ones - a process that requires BDNF-dependent protein synthesis. Growth hormone secreted during the first slow-wave sleep episode drives BDNF gene transcription via IGF-1 signaling. Sleep deprivation acutely reduces hippocampal BDNF expression in animal studies, and chronic sleep restriction progressively depletes BDNF protein in brain tissue.
Diet and BDNF
DHA (omega-3): Docosahexaenoic acid is the primary structural fatty acid of neuronal membranes, and one of the most abundant fatty acids in the brain. DHA is required for TrkB receptor function and influences BDNF mRNA expression. Dietary DHA deficiency reduces hippocampal BDNF expression in animal studies, and omega-3 supplementation raises BDNF in human clinical trials. Curcumin: In animal studies, curcumin activates Nrf2 and increases BDNF mRNA in several brain regions. Human evidence is limited. Flavonoids: Epicatechin from dark chocolate, anthocyanins from blueberries, and luteolin from celery have all demonstrated BDNF-activating effects in human or rodent studies. The mechanism appears to involve CREB phosphorylation via MAPK signaling, directly driving BDNF gene expression.5
References
- 1Barde YA, et al. "Purification of a new neurotrophic factor from mammalian brain." EMBO J. 1982;1(5):549-53. PubMed · DOI
- 2Huang EJ, Reichardt LF. "Neurotrophins: roles in neuronal development and function." Annu Rev Neurosci. 2001;24:677-736. PubMed · DOI
- 3Szuhany KL, et al. "A meta-analytic review of the effects of exercise on brain-derived neurotrophic factor." J Psychiatr Res. 2015;60:56-64. PubMed · DOI
- 4Erickson KI, et al. "Exercise training increases size of hippocampus and improves memory." Proc Natl Acad Sci U S A. 2011;108(7):3017-22. PubMed · DOI
- 5Spencer JP. "The impact of flavonoids on memory: physiological and molecular considerations." Chem Soc Rev. 2009;38(4):1152-61. PubMed · DOI
- 6Gejl AK, et al. "Associations between serum and plasma brain-derived neurotrophic factor and influence of storage time and centrifugation strategy." Sci Rep. 2019;9(1):9655. PubMed · DOI
- 7Klein AB, et al. "Blood BDNF concentrations reflect brain-tissue BDNF levels across species." Int J Neuropsychopharmacol. 2011;14(3):347-53. PubMed · DOI
- 8Molendijk ML, et al. "Serum BDNF concentrations as peripheral manifestations of depression: evidence from a systematic review and meta-analyses on 179 associations (N=9484)." Mol Psychiatry. 2014;19(7):791-800. PubMed · DOI
