This week I am taking a look at two hormones that affect our mood, mental health and so much more – serotonin and dopamine.


When we think of serotonin we think of “happy”, as this is a chemical related to our mood. However, serotonin is not only a mood stabiliser, but also plays a role in our digestion, eating and sleep.

Serotonin is made from the essential amino acid, tryptophan, (essential meaning that it must enter your body through diet) and is a chemical produced by nerve cells. Approximately 95% of serotonin is made in the digestive tract by gut bacteria, but it is also found in blood platelets and throughout the central nervous system.

In the brain serotonin is associated with happiness, regulating anxiety, and keeping mood stable. Low levels of serotonin are linked to depression, although its role as an anti-depressive, and indeed how much it contributes to depression, are still widely unknown, even after many years of research. Increasing levels of serotonin via medication can have unwanted effects such as reduced libido and decreased arousal. High levels may also contribute to issues with bone health such as osteoporosis.

When we have eaten something that causes us to feel sick, serotonin levels are increased, which stimulates the area of the brain that controls nausea. Because serotonin is made in the gut it is found primarily in the stomach and intestines and plays a role in controlling bowel function, which would explain why a rise in production of serotonin when we have eaten something bad will also cause us to experience diarrhoea in its attempt to rid the body of unwanted bacteria and toxins.

Although melatonin is the principle hormone in regulating our sleep and wake cycles, serotonin also plays a part. It stimulates areas of the brain and whether you feel sleepy or wakeful depends on which area has been stimulated, and which serotonin receptor is used.

As we age the production of serotonin is often reduced, which can contribute to sleep disorders in later life. Exercise has been demonstrated to stimulate the pathways of serotonin production eliciting “acute elevations in forebrain serotonin concentrations, an effect that waned upon cessation of exercise. But it seems that appropriate dosage is necessary as overtraining has been linked to serious maladaptations of serotonin production, which is accompanied by insomnia. So, if you are constantly training and find that your sleep is being affected, you may want to take a look at cutting back a little. However, on the positive side, exercise can accelerate the re-synchronisation of the body’s circadian clock to new light and dark cycles, which is thought to be due to the increased activity of brain serotonergic projections.

When you have a wound, serotonin is released from the blood platelets to help heal them. It does this by narrowing tiny arteries and forming blood clots.

Because the majority of serotonin is formed in the GI tract, it plays a critical role in the health of the gut and also in brain-gut communication. Research shows that serotonin mediates intestinal motility (the movement of food through the digestive tract), mediates intestinal secretion within the GI tract and also modulates perception in the bowels. Treatment with serotonergic agents has been used with patients suffering from IBS to help maintain normal gut function and brain-gut communication, however there is also evidence that certain serotonergic drugs can induce serotonin syndrome. This is a group of symptoms that react against some of the drugs used for serotonin treatments. These can range from mild to severe and include:

  • Agitation
  • Restlessness
  • Confusion
  • Rapid heart rate
  • High blood pressure
  • Dilated pupils
  • Loss of muscle co-ordination
  • Twitching muscles
  • Muscle rigidity
  • Sweating
  • Diarrhoea
  • Nausea
  • Headaches

Sunlight And Serotonin

Seasonal Affective Disorder (SAD) is linked to the relationship between sunshine and serotonin. Human skin appears to have the ability to generate serotonin from the sun, and the lack of this can manifest in symptoms such as depression, anxiety and has even been linked to suicide. Exposure to sunlight releases serotonin, whilst decreased exposure has been associated with lower levels of serotonin which, in turn, is linked to major depressive disorders. One of the treatments for SAD is via light box therapy, or phototherapy, which stimulates the brain to produce serotonin and reduce melatonin.


Like serotonin, dopamine is a chemical released by neurons in order to send signals to other nerve cells. It is a precursor to the synthesis of the neurotransmitters epinephrine (adrenaline) and norepinephrine (noradrenaline).

There are several different pathways that dopamine utilises which affect emotions, movement, learning, motivation, pleasure and pain, and perhaps the most well known – the reward system. Eating, playing, sex, and other activities that bring us pleasure all increase our levels of dopamine. Perhaps more accurately, dopamine confers motivational salience, which means that it causes us to take action to move towards, or away from, the things that will bring us pleasure or pain. This mechanism is known as the mesolimbic pathway, in which information passed on from the stimulus (for example, sex or eating something sugary) travels from the ventral tegmental area (VTA) in the brain to the nucleus accumbens and up to the prefrontal cortex. This then activates hormones such as dopamine to tell us that this experience was really good and encourage us to repeat it.

Low levels of dopamine are linked to a reduction in motivation and enthusiasm. Serious down-regulation of dopamine production is thought to be a cause in Parkinson’s disease as well as being associated with ADHD, schizophrenia, depression, anxiety, Huntingdon’s disease and OCD. In Parkinson’s disease there is also a loss of dopamine-secreting neurons, which leads to motor impairment.

In cases such as depression and anxiety, inactive dopamine receptors connected to pathways that are responsible for motivation, pleasure and reward may be the reason that these conditions occur. Conversely, over-activation that floods the brain with too much dopamine may be the cause of neuropsychiatric conditions such as schizophrenia and drug addiction. Antipsychotic drugs reduce dopamine levels and instead induce anhedinoa, which is a diminished ability to experience pleasure.

Dopamine has many functions within the body including:

  • Blood vessels – it inhibits norepinephrine release and acts as a vasodilator, widening the vessels.
  • Kidneys – it increases sodium excretion and urine output.
  • Digestive system – it reduces gastrointestinal motility (movement) and protects the gut mucosa, which lines the intestinal wall.
  • Pancreas – it reduces insulin production.
  • Immune system – it reduces lymphocytes, the white blood cells which include killer cells, T cells and B cells. It can also affect immune cells in the spleen, bone marrow, and circulatory system.
  • Behaviour – it is a key factor in modulating motivational behaviours, providing a learning signal for future behaviour. Different levels at different times can produce slightly different outcomes, such as reward rate and motivational vigour, or estimating a value on future work outcomes.

Processed Food And Dopamine

When you eat sugar it triggers dopamine release and, over time with regular or chronic consumption, can actually change the gene expression and availability of dopamine receptors in the brain. It also inhibits the action of the dopamine transporter, which is the protein responsible for moving dopamine out of the synapse and back into the neuron. Artificial sweeteners also produce similar effects. So what this means is that regular consumption of sweet products results in the need for even more sugary stimuli to produce the same “high” effect because the brain has become tolerant to the sugar dose – and needs more. Just like drugs.

A similar situation is found with high omega 6 polyunsaturated oils, which can trigger overeating, due to the body producing endocannibinoids – effectively resulting in having the “munchies” (again, similar to taking drugs). These endocannabinoids stimulate more dopamine production. Chronic consumption of these vegetable and seed oils locks in our reward system/mechanism via dopamine and we continue to eat, or feel hungry, even though we are full.

Exercise And Dopamine

It is well established that exercise improves mood and brain function, and this is likely due to increased levels of dopamine during exercise. One trial looked at how much exercise is required to improve mental health and found that at after 10 minutes improvements in vigour, fatigue and total mood started to occur, with more benefits appearing after 20 minutes or more. Another study looked at cross-sectional data of 44 healthy individuals of varying ages and discovered that typical age-related dopamine D2 receptor loss was significantly lower in those who were physically active as opposed to those who were inactive.

Both serotonin and dopamine are related to fatigue and performance. They influence the feelings that lead to reduced intensity or actual interruption of exercises being performed. Rodent experiments indicate that increasing serotoninergic activity during exercise results in reduced performance, whereas increasing dopaminergic activity results in increased performance. This is difficult to replicate in humans, however, as unlike the rodent studies which use direct manipulation of brain serotonin and dopamine, human trials rely on supplementation through nutrition or drug interventions. This has produced conflicting results and the only valuable effect observed is that the ratio between serotonin and dopamine appears to be more relevant for determining fatigue, rather than attempting to manipulate one or the other.

What Happens When You Are Sleep Deprived?

This is an interesting double-edged sword because there is evidence to show up-regulation in the production of dopamine after one night’s sleep deprivation, but research also demonstrates a reduction in the number of dopamine receptors. And, although we may produce more dopamine after pulling an all-nighter, this does not compensate for the reduced cognitive function that results from lack of sleep. The study’s authors stated; “these findings suggest dopamine may increase after sleep deprivation as a compensatory response to the effects of increased sleep drive in the brain”, meaning that extra dopamine is required to help you stay awake after a night of little to no sleep, and this could be related to the body’s natural desire to keep to a circadian rhythm.

The Takeaway

Normal hormone function is critical to good health and taking steps to optimise them doesn’t need to be hard. Here are a few things you can do to keep your hormones in tip top shape:

  • Get out every day in nature
  • Get adequate sleep every night
  • Avoid sugar
  • Avoid omega 6 vegetable and seed oils
  • Include regular bouts of exercise every week
  • Get some sun on your skin whenever possible
  • Eat real, whole foods
  • Try and get your body in synch with a natural circadian rhythm

For more information and help on getting your hormones back on track click here to schedule a consultation.