The fountain of youth has not yet been found, but swimming is the closest we have.

It's no secret that aerobic exercise can help reverse some of the ravages of aging. A growing body of research shows that swimming can provide a unique boost to brain health. Regular swimming has been shown to improve memory, cognitive function, immune response, and mood. Swimming can also help repair damage from stress and forge new neural connections in the brain.

But scientists are still trying to figure out how and why swimming, in particular, produces these positive effects on the brain. What is certain is that if more adults knew about the cognitive and mental health benefits of swimming, they might be more willing to jump in the pool or sea with their children.

Creating new and improved brain cells and connections

Until the 1960s, scientists believed that the number of neurons and synaptic connections in the human brain was finite and that, once destroyed, these brain cells could not be replaced. But that idea was overturned as researchers began to see abundant evidence of the birth of neurons, or neurogenesis, in the adult brains of humans and other animals.

Now, there is clear evidence that aerobic exercise can contribute to neurogenesis and play a key role in reversing or repairing damage to neurons and their connections in both mammals and fish.

Research suggests that one of the key ways these changes occur in response to exercise is through increased levels of a protein called brain-derived neurotrophic factor. The neuronal plasticity – or the brain’s ability to change – that this protein stimulates has been shown to enhance cognitive function, including learning and memory.

Human studies have found a strong link between circulating concentrations of brain-derived neurotrophic factor and increased size of the hippocampus, the region of the brain responsible for learning and memory. Increased levels of brain-derived neurotrophic factor have also been shown to sharpen cognitive performance and help reduce anxiety and depression. Conversely, researchers have observed mood disorders in patients with lower concentrations of brain-derived neurotrophic factor.

Aerobic exercise also promotes the release of certain chemical messengers called neurotransmitters. One of these is serotonin, which – when present in increased levels – is known to reduce depression and anxiety and improve mood.

In studies in fish, scientists observed changes in genes responsible for increasing levels of brain-derived neurotrophic factor, as well as enhanced growth of dendritic spines – protrusions on the dendrites, or elongated sections of nerve cells – after eight weeks of exercise compared to the control group.

This complements studies in mammals where brain-derived neurotrophic factor is known to increase the density of spinal neurons. These changes have been shown to contribute to improved memory, mood, and enhanced cognition in mammals. Greater spine density helps neurons make new connections and send more signals to other nerve cells. With repetition of signals, the connections can become stronger.

What's so special about swimming?

Researchers don’t yet know what the secret “recipe” of swimming might be. However, they are getting closer to understanding it. Swimming has long been recognized for its cardiovascular benefits. Because swimming involves all major muscle groups, the heart has to work hard, which increases blood flow throughout the body. This leads to the formation of new blood vessels, a process called angiogenesis. The increased blood flow can also lead to a large release of endorphins – hormones that act as natural pain relievers throughout the body. This increase brings about the feeling of euphoria that often follows exercise.

Most research into how swimming affects the brain has been done in rats. In one study, swimming was shown to stimulate brain pathways that suppress inflammation in the hippocampus and inhibit apoptosis, or cell death. The study also showed that swimming may help support neuronal survival and reduce the cognitive effects of aging. While researchers don’t yet have a way to image neuronal apoptosis and survival in humans, they are seeing similar cognitive effects.

One of the most tantalizing questions is how, specifically, swimming enhances short-term and long-term memory. To determine how long the beneficial effects might last, the researchers trained rats to swim for 60 minutes daily, 5 days/week. The team then tested the rats' memory.

After just 7 days of swimming training, the researchers saw improvements in both short-term and long-term memory, based on the reduction in the number of errors the rats made each day. The researchers suggested that this boost in cognitive function could form the basis for using swimming as a way to repair learning and memory impairments caused by neuropsychiatric diseases in humans.

While the leap from rat studies to humans is significant, human research is producing similar results that suggest a clear cognitive benefit from swimming at all ages. For example, in a study that examined the impact of swimming on mental acuity in older adults, researchers concluded that swimmers had improved mental speed and attention compared to non-swimmers.

However, this study is limited in its research design, as participants were not randomized, so those who were swimmers before the study may have had an unfair advantage. The details of the time or laps required, the swimming style, and the cognitive adaptations and pathways activated by swimming are still under investigation. But neuroscientists are getting much closer to piecing it all together. For centuries, people have searched for the fountain of youth. Swimming may be the closest we can get.

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