Serotonin And Exercise

Overview

Exercise increases the brain levels of serotonin, dopamine and norepinephrine; which, together with others, are collectively known as ‘happy brain chemicals’.

Exercise is helpful in improving mood and cognition, especially in anxiety and depression, and has been associated with increased serotonin levels in the brains of animals, and humans.

Serotonin is a neurotransmitter and hormone that plays a part in regulating mood, appetite, sleep, memory and more.  It can also help with gut function, insulin production and metabolism. While the body naturally produces serotonin, we can induce serotonin production by exercising. Regular exercise has been shown to increase serotonin levels, which helps improve mood and memory. 

Understanding serotonin and exercise

Serotonin

Known as one of the ‘happy chemicals’ in the brain, serotonin is a neurotransmitter, i.e., a chemical messenger that neurons use to communicate with each other. You might have heard the term ‘serotonin boost’ being used colloquially to describe the wave of ecstasy or euphoria experienced after some joyful incidents,this is because an increase in serotonin levels in certain brain regions actually helps boost your mood. Some antidepressants therefore work by increasing serotonin levels between neurons. Depending on which brain regions the serotonin is released in,  it can regulate different high functions of the brain, including mood, appetite, sleep, memory and brain development.¹  

While the brain serotonin is mainly produced in the brainstem (the stalklike section of the brain that joins to the spinal cord), up to 95% of serotonin in our body is actually produced in peripheral organs, mainly the gut.¹ This peripheral serotonin (i.e., not in the brain) either acts locally in the organs that produce it or gets released into the bloodstream where it acts as a hormone. Peripheral serotonin cannot cross the blood-brain barrier to enter the brain.  So, technically, peripheral serotonin functions independently from that in the brain,   to play  important roles in promoting insulin secretion and regulating glucose and fat metabolism.

Exercise

From preventing obesity and heart diseases, to reducing the risk of cancers and mental health conditions, regular exercise plays an important role in maintaining good health. 

The main types of exercise  are aerobic and anaerobic.  Even though both these types can improve heart health and help with weight management, they work in different mechanisms. 

Aerobic exercise

Aerobic exercises utilise the energy generated from breaking down glucose under a  constant oxygen supply  to the muscles,  thus helping build endurance.  Some examples of aerobic exercises include jogging, hiking, cycling and swimming. 

Anaerobic exercise

On the other hand, anaerobic exercises are intense physical activities that utilise energy generated from breaking down glucose and fats in the absence of oxygen.  The energy  generated  in the presence of oxygen is higher, the effects of aerobic exercises are sustained for longer compared to those produced during anaerobic exercise. Examples of anaerobic exercises include high-intensity interval training (HIIT), sprinting and power-lifting.² For adults, it is recommended to get at least 20-25 minutes of moderate exercise every day.² 

The link between serotonin and exercise

Effects of exercise on serotonin

Whether you wish to increase your serotonin level to boost your mood or improve your digestion, one of the natural ways you can do that is by exercising. 

Research has shown that during exercise, serotonin production in certain brain regions is increased. Exercise stimulates the breakdown of fats into free fatty acids, which are important in facilitating the transport of available tryptophan into the brain.³ Tryptophan is the amino acid that serotonin is made from, so an increase in its availability during and after exercise will increase the level of serotonin that can be produced. Besides that, the increase in muscle activity during aerobic exercise also augments the uptake of branched-chain amino acids (BCAAs) by the muscles.⁴ As the BCAAs can compete with tryptophan to enter the brain, more of these BCAAs getting taken up by muscles actually allows more tryptophan to enter the brain to supply serotonin production.⁴ 

As mentioned above, an increase in serotonin level in the brain can improve mood, sleep, and even memory. Exercise has been shown to increase the serotonin levels in the hippocampus, which is an important brain region involved in memory and mood. The increase in serotonin levels due to exercise may also help improve mood and memory by facilitating the generation of new neurons in the hippocampus.⁵ 

Among different types of exercise, it appears that aerobic exercises are more effective in elevating serotonin levels than anaerobic exercise. In a study done on a group of male students in early adulthood, aerobic exercise caused a significant post-exercise rise in plasma serotonin levels, whereas anaerobic exercise and resistance training did not.⁶ Techniques of aerobic exercise used in this study were mainly running. However, others such as cycling and swimming are also great alternatives for achieving similar effects. 

Serotonin promotes nutrient absorption and storage in the gut, so an increase in the level of peripheral serotonin after exercise is probably beneficial for gut function as well.⁷ Besides that, serotonin also promotes the release of insulin from the pancreas. Insulin is a hormone essential for glucose homeostasis. Regular exercise may therefore help control the blood glucose levels through the action of serotonin, which is increased after exercise.⁷  

The increase in serotonin production both in the brain and peripherally induced by exercise depends on the intensity of the exercise done.  A study that had been conducted in 2016 suggested that only high-intensity continuous exercise managed to significantly increase the plasma serotonin level.  However, a later study in 2022 reported a significant increase in the plasma serotonin levels only after moderate-intensity continuous aerobic exercise.⁸ Regardless, the general recommendation for maintaining good health is to do a combination of both moderate (~50% - 70% of your maximum heart rate) and high-intensity (~70% - 85% of your maximum heart rate) aerobic exercises throughout the week.

Summary

Serotonin is a neurotransmitter in the brain that plays a part in regulating mood, appetite, sleep, memory and more. Serotonin in the periphery, though, acts as a hormone that can help with gut function, insulin production and metabolism. While the body naturally produces serotonin, we can induce further serotonin production by exercising. Regular exercise has been shown to increase serotonin levels, which helps improve mood and memory.