Cognitive Benefits of Swimming: Research on Neurogenesis in the Hippocampus from Regular Swimming

The “Hidden” Benefits of Swimming: Rejuvenating the Brain

When most people talk about the health benefits of swimming, the focus is often on improved cardiorespiratory fitness, muscle strengthening, and weight management. However, neuroscience research accumulated over the past 20 years has revealed a deeper, more remarkable impact of swimming on the brain: swimming can promote neurogenesis in the adult brain, particularly in the hippocampus, which is closely linked to learning and memory, and produces significant benefits for cognitive function, emotional regulation, and the prevention of neurodegenerative diseases.

Neurogenesis in the Adult Brain: Breaking Old Beliefs

For a long time, the neuroscience community believed that neurons in the brain no longer proliferate after adulthood—“once brain cells die, they’re gone” was the common understanding. However, research since the 1990s has completely changed this notion:

• In 1998, Eriksson and colleagues published a landmark paper in Nature Medicine, confirming for the first time that neurogenesis occurs in the hippocampus of adult human brains
• Subsequent research found that aerobic exercise is currently the most powerful non-pharmacological means of promoting adult neurogenesis
• Swimming, as a form of aerobic exercise, has shown particularly pronounced neurogenesis-promoting effects in animal models

The Hippocampus: The Core of Memory and Emotion

Molecular Mechanisms of Swimming-Promoted Neurogenesis

1. The Core Role of BDNF (Brain-Derived Neurotrophic Factor)

Brain-Derived Neurotrophic Factor (BDNF) is the most important regulatory molecule for neurogenesis, often called the “fertilizer of the brain”:

• After swimming training (in animal models), hippocampal BDNF mRNA expression increases by approximately 100–200%
• BDNF activates the TrkB receptor, promoting the differentiation of neural stem cells into mature neurons
• BDNF also enhances the plasticity of existing synapses (long-term potentiation, LTP)
• In human subjects, after 12 weeks of aerobic swimming training, serum BDNF concentrations increased by an average of approximately 15–30%

2. The Supporting Role of IGF-1 (Insulin-Like Growth Factor 1)

• IGF-1 secreted by skeletal muscles during exercise can cross the blood-brain barrier and enter the brain
• IGF-1 works synergistically with BDNF to promote hippocampal neurogenesis
• Swimming (aerobic in nature) stimulates IGF-1 more effectively than resistance training

3. Serotonin (5-HT) and Dopamine Systems

• Aerobic swimming training increases serotonin receptor density in the hippocampus
• Normalization of the serotonin system is directly related to anti-anxiety and antidepressant effects
• The “swimmer’s high” after swimming is partly mediated by the dopamine and endocannabinoid systems

4. Anti-Inflammatory Mechanisms

• Chronic low-grade inflammation is a significant risk factor for neurodegenerative diseases
• Regular swimming lowers serum levels of pro-inflammatory cytokines such as C-reactive protein (CRP) and IL-6
• The anti-inflammatory effect protects hippocampal neurons and reduces neural damage caused by inflammation

Key Findings from Animal Models and Human Studies

Animal Studies

Extensive rodent studies have shown:

• Water maze test: Rats that swam regularly (30–60 minutes daily for 4–8 weeks) found the platform 30–50% faster than the non-exercise group in the Morris water maze (a spatial memory test)
• Hippocampal volume: The number of newborn neurons in the dentate gyrus (the primary region of neurogenesis) of swimming rats increased 2–3 fold
• Anxiety behavior: Swimming groups showed significantly increased exploratory behavior in the open field test, indicating reduced anxiety

Human Cohort Studies

Although human studies face greater technical limitations (hippocampal neurons cannot be directly counted), imaging and cognitive testing studies still provide strong indirect evidence:

Differences in Neural Benefits: Swimming vs. Other Aerobic Exercise

This is an interesting scientific question: are the neural benefits of swimming the same as those of other aerobic exercises such as running or cycling?

Potential unique advantages of swimming:

1. Sensory stimulation from water: The tactile stimulation of skin contact with water (mechanoreception) may additionally activate the cerebral cortex, providing richer sensory input than land-based exercise
2. Cerebral blood flow effects of a horizontal posture: The horizontal position in water allows for better venous return, resulting in more stable cerebral blood flow than upright exercise
3. Benefits of breathing rhythm: The enforced breathing rhythm of swimming may resemble meditative rhythmic breathing, providing additional vagus nerve stimulation
4. Social environment: If participating in swimming classes, social interaction itself is a neuroprotective factor

Note: High-quality human studies directly comparing the neural benefits of swimming versus running remain limited; most conclusions are based on animal studies or indirect inference.

Swimming Strategies to Optimize Neural Benefits

Based on existing research, the following strategies can maximize the positive effects of swimming on the brain:

1. Frequency: At least 3 times per week; research shows that the effects of “fewer than 2 times per week” are significantly lower than “3 or more times per week”
2. Intensity: Moderate intensity (approximately 60–70% of maximum heart rate, Z2–Z3) is the optimal zone for neural benefits; very low intensity (Z1) has limited effects, while very high intensity (Z5+) may suppress neurogenesis due to excessive stress hormones (cortisol)
3. Duration: At least 30–45 minutes per session; research shows that BDNF only rises significantly after 20–30 minutes of aerobic exercise
4. Long-term consistency: The benefits of neurogenesis require continuous accumulation; benefits begin to fade after 4–6 weeks of training interruption
5. Incorporate skill learning: Learning new swimming techniques (such as learning breaststroke or improving flip-turn breathing) engages the procedural memory system, providing additional neural plasticity stimulation to the cerebellum and basal ganglia

Special Significance for Taiwanese Society

Taiwan is facing the demographic challenge of rapid population aging, and dementia prevention is an important public health issue:

• The prevalence of dementia among people aged 65 and above in Taiwan is approximately 7–8%
• Approximately 10,000–20,000 new dementia patients are diagnosed each year
• Regular aerobic exercise (including swimming) is listed by the medical community as a first-line lifestyle intervention for dementia prevention
• Swimming is joint-friendly and particularly suitable for middle-aged and older adults with existing knee joint degeneration, making it “the closest to an all-age-friendly” exercise for dementia prevention

Conclusion

Research showing that swimming promotes neurogenesis in the brain’s hippocampus gives this ancient water sport a whole new scientific significance. When we slip into the pool and begin each training session, we are not just working our muscles and cardiovascular system—we are also reshaping the brain at the molecular level. From BDNF secretion to the formation of new neurons, swimming is currently one of the most scientifically effective ways to “maintain the brain.” This knowledge is the best reason for every swimming enthusiast in Taiwan, a society on the verge of becoming a super-aged one, to get into the water.

Related Reading

• Exercise and Brain Neuroplasticity: Aerobic Training Research on Hippocampal Neurogenesis
• The Impact of Swimming on Children’s Cognitive Development: Latest Findings in Neuroscience and Education Research
• Swimming and Cognitive Health in Older Adults: The Preventive Benefits of Water Aerobics Against Dementia
• The Benefits of Long-Term Aerobic Training on Cognitive Function: Research on Hippocampal Volume and BDNF