Serotonin Hormone Function

Serotonin is a key neurotransmitter and hormone that operates within the body. It is fundamental for many bodily processes, physiological health as well as psychological health. Therefore, due to its importance, deficient levels of serotonin bring with it an array of negative repercussions, particularly mental health problems. To correct this individuals can take certain foods, supplements and medications, in addition to adopting certain behaviours to help rectify this deficiency and continue functioning as optimally as possible. However, it should be noted that too much serotonin can also be detrimental by increasing the risk of serotonin syndrome. Overall, maintaining healthy levels of serotonin is essential for normal functioning. Therefore, if you are experiencing any concerns regarding this, then consider consulting a healthcare professional for assistance.   

What is serotonin?

Serotonin, also known as 5-hydroxytryptamine (5-HT), is both a monoamine neurotransmitter and hormone depending on where in the body it operates. Fundamentally, serotonin functions as a chemical messenger carrying signals throughout the brain itself (i.e., the central nervous system) as well as to other areas of the body (i.e., the peripheral nervous system).

Serotonin is essential for various bodily functions within the central nervous systems, such as learning and memory, happiness and reward, sleep regulation, behaviour, and appetite.¹ In terms of emotional regulation, serotonin is considered a ‘happy hormone’ considering it plays a role in a positive mood, emotions and calmness. In turn, due to their involvement in such fundamental functions, serotonin is thought to play a pivotal role in mental health conditions, such as depression, anxiety and other affective disorders.²

What does serotonin do in my body?

Serotonin is highly multifunctional therefore it plays a pivotal role in many physiological and psychological bodily processes. Here are some of the main functions and processes that serotonin influences inside the body:

Digestion and bowel movement

Approximately 90% of the serotonin within the body is produced by the intestines.³ Given its location in the gastrointestinal tract, ( serotonin helps with protecting the gut,⁴ normal bowel function and regulating appetite whilst eating. The gut can also increase serotonin release to promote digestion by accelerating the movement of irritating foods or toxic products that may have been consumed. This leads to quicker expulsion from the body.

Mood

Tthanks to its involvement in regulating feelings, such as happiness and anxiety, serotonin has been widely linked to affect, emotional stability, and mood. Therefore it plays a significant role in terms of one’s sense of well-being. As a result of this, serotonin has been the target of various medications for numerous mental health conditions and mood disorders.² In particular, selective serotonin reuptake inhibitors (SSRIs) work to increase the serotonin levels in the brain, in hope of yielding a positive mood effect to help combat anxiety and depression.

Nausea

In response to illness, certain foods, or other conditions the body increases the amount of serotonin present in the gut to initiate nausea and vomiting.⁵ While serotonin is released at a faster rate the gut is not able to digest it fast enough, causing the brain to interpret this chemical message as nausea. In corroboration with this, drugs that target specific serotonin receptors in the brain help diminish such feelings of nausea and vomiting.⁶

Blood clotting and wound healing

In response to bodily damage that requires repair, in particular, tissue damage, platelets within the blood release their stores of serotonin to help stop the bleeding and heal the wound.⁷ This increase in serotonin slows blood flow by causing small arteries (also referred to as arterioles which carry blood away from the heart) to narrow, a process termed vasoconstriction.⁸ Consequently, these elements of constricted blood flow contribute to blood clotting.

Sleep

Various neurotransmitters, including serotonin and dopamine, play vital roles when it comes to sleep. More specifically, serotonin is required to make a key sleep hormone, termed melatonin, which helps one fall asleep; therefore it is vital for a fully functioning sleep cycle. Consequently, too much or too little serotonin can affect sleep patterns and quality. Moreover, the specific brain areas responsible for regulating sleep possess serotonin receptors, making serotonin a significant contributor to the process of sleep.

Bone health/density

Serotonin is implicated in bone density which refers to the strength of one’s bones. Elevated serotonergic levels within the gut are thought to be associated with lower bone density which increases the risk of suffering bone fractures and conditions such as osteoporosis.

Sexual function

Serotonin can control one’s sexual functioning by influencing the frequency and intensity of sexual feelings and desires. This could potentially explain why certain medications affecting serotonin, such as selective serotonin reuptake inhibitors, are associated with sexual side effects such as decreased sexual desire, difficulty becoming and sustaining arousal, and challenges reaching orgasm.⁹ 

What problems are associated with low serotonin levels?

There are various problems that are associated with low serotonin, these include:

• Immunity – The overall functioning of the immune system contributes to serotonin-related processes
• Gastrointestinal issues – Issues with the digestive process as well as bowel movements and functions. Also, the implication with appetite could be bi-directional as it could be increased or decreased
• Physical health conditions – Serotonin deficiency is associated with physical conditions including obesity, diabetes, cardiovascular disease, fatigue, osteoporosis, and gastrointestinal issues
• Mental health conditions – Deficient serotonin levels in the brain are thought to be heavily implicated in depression therefore it is a popular target for antidepressant drugs, such as selective serotonin reuptake inhibitors. These drugs prevent the body from reabsorbing the neurotransmitter so that more is left available for circulation¹⁰

Additionally, other medications targeted towards regulating serotonin levels help treat other disorders, such as bipolar disorder, post-traumatic stress disorder, obsessive-compulsive disorder, and panic disorders amongst various others.

Nevertheless, with all these conditions, there remains speculation regarding the causal nature of serotonin in causing these conditions. However,regardless serotonin is still seen to play a substantial role when it comes to mental health. 

What can cause low serotonin levels?

Serotonin deficiency refers to deficiency (i.e., low levels) of serotonin within the body, more specifically the brain, which then results in various predominantly negative behavioural and emotional repercussions.

Whilst there is no clear, definitive cause of low serotonin levels it is often attributed to either:

1. Not having enough serotonin in the body – The body may not be producing enough serotonin to maintain normal levels which could be due to biological factors, such as genetics and hormonal changes, or other factors, such as nutritional and vitamin deficiencies
2. Inefficient use of serotonin – There may be enough serotonin present within the body but if it is not being used properly then problems arise. Inefficient serotonin use could be the result of not having enough serotonin receptors or faulty receptors which absorb and break down serotonin either too quickly or slowly¹¹

What can I do to increase serotonin levels?

There are various ways to increase serotonin levels which can be achieved through nutrition and diet, supplements, medication and other natural means.

Foods to increase serotonin levels

Fundamentally serotonin is made from tryptophan, an essential amino acid occurring in some foods that enters the body through one’s diet. Examples of foods that typically contain tryptophan include meat, eggs, dairy and soy products, as well as nuts. Tryptophan is used by the body to create serotonin, and so eating foods with high tryptophan content can support this process.

However, just eating foods high in tryptophan does not necessarily mean it will be absorbed and used to boost serotonin levels. This is because this is merely one step in the process. Firstly, to absorb this amino acid, our bodies need carbohydrates to release insulin to absorb tryptophan into the blood. Once within the blood tryptophan competes with other amino acids to get absorbed by the brain. There this is a complex process that scientists are continuing to study to uncover exactly how this all implicates serotonin levels.

Alongside tryptophan, our bodies also require other nutrients, such as vitamins and omega-3 fatty acids to produce serotonin.¹² Examples of foods containing these key nutrients include bananas, beans, leafy greens as well as nuts and seeds. Overall, a generally rich diet containing these nutrients and amino acids helps promote the healthy functioning of gut bacteria which has been linked to adequate serotonin levels.¹³

Supplements to increase serotonin levels

Alongside a healthy diet containing the necessary nutrition, there are certain supplements that can help improve serotonin levels. Examples of such supplements include:

• 5-HTP
• Probiotics
• St. John’s wort
• SAMe (S-adenosyl-L-methionine)

Crucially, whilst taking supplements can indeed raise serotonin levels, there is also an increased risk for serotonin syndrome, alternative side effects and interactions. Therefore, it is vital to consult a healthcare professional.

Medications to increase serotonin levels

Certain medications can be taken to increase serotonin levels by promoting serotonergic activity within the brain. Commonly, such medications are broadly termed antidepressants given that, because they work within the brain to increase serotonin levels, they often result in improvements in mood and emotional regulation.¹⁴ Therefore, such medication is thought to be an effective treatment for mental health conditions such as depression, anxiety and other mood disorders.

However, when taking medication that affects serotonin, other medications or supplements that also act on serotonin should not be taken without consulting a healthcare professional first. In the event such medications are mixed there is an increased risk of facing serious ramifications such as serotonin syndrome.

Selective Serotonin Reuptake Inhibitors (SSRIs) –

Selective serotonin reuptake inhibitors (SSRIs) work by increasing the amount of serotonin in the brain. During chemical messaging in the brain, the reuptake of the neurotransmitter serotonin is blocked therefore leaving more serotonin available at the site of transmission so that signals can propagate further on throughout the brain to the necessary neural region.¹⁵

Examples of selective serotonin reuptake inhibitors include:

• Citalopram (Celexa®)
• Escitalopram (Lexapro®)
• Paroxetine (Paxil®)
• Fluoxetine (Prozac®)
• Sertraline (Zoloft®)

Selective Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs)

Selective serotonin-norepinephrine reuptake inhibitors (SNRIs) also work by increasing the amount of serotonin in the brain. Similar to SSRIs, during chemical messaging in the brain, the reuptake of serotonin and norepinephrine are blocked therefore leaving more of these neurotransmitters available at the site of transmission so that signals can propagate further on throughout the brain to the necessary neural region.¹⁶

Examples of selective serotonin-norepinephrine reuptake inhibitors include:

• Duloxetine (Cymbalta®)
• Venlafaxine (Effexor XR®)

Other Classes of Antidepressants (TCAs & MAOIs) –

Tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs) are thought to be older classes of antidepressants that are less commonly prescribed by today’s standards due to their adverse side effects and lethality in overdose quantities.¹⁷

Tricyclic Antidepressants (TCAs):

TCAs work by affecting serotonin levels in the brain. Similar to SSRIs and SNRIs, they block the reuptake of serotonin and norepinephrine thereby leaving more of these neurotransmitters available at the site of transmission so that signals can propagate further on throughout the brain.

Examples of tricyclic antidepressants include:

• Amitriptyline (Elavil®)
• Nortriptyline (Pamelor®)
• Trimipramine (Surmontil®)
• Imipramine (Tofranil®)

Monoamine oxidase inhibitors (MAOIs):

MAOIs ultimately work by increasing the amount of neurotransmitters available in the brain. More specifically, MAOIs work by blocking the effects of the monoamine oxidase enzyme which typically breaks down serotonin, epinephrine and dopamine.¹⁸ Therefore, by preventing this breakdown, more neurotransmitters remain available at the site of transmission. This leads to further propagation of signals throughout the brain.

Examples of tricyclic antidepressants include:

• Isocarboxazid (Marplan®)
• Phenelzine (Nardil®)
• Tranylcypromine (Parnate®)

It should be noted that MAOIs are rarely prescribed nowadays but are sometimes prescribed in certain circumstances by a specialist doctor.

Natural boosters to increase serotonin levels

Here are some natural remedies or strategies that can help you to boost serotonin levels in the body and improve overall mood:

• Sunlight exposure – Exposure to bright light can help improve mood, hence why light therapy is a common treatment for seasonal affective disorder (SAD)¹⁹ especially during the winter months when there is limited access to bright sunlight. Sunlight is also pivotal for boosting vitamin D levels necessary for serotonin production
• Regular exercise – Exercise, in particular aerobic exercise, can have mood-boosting effects, improves physicality, and triggers the release of happy hormones such as serotonin and dopamine
• Practicing meditation – Meditation helps relieve stress and promotes optimism. It is also thought to raise serotonin levels²⁰
• Massage therapy – Promotes the release of serotonin and decreases cortisol (the body’s stress hormone). Can even be effective when not administered by a trained massage therapist,²¹ therefore the mere act of receiving a massage has vital benefits

Despite there not being enough scientific evidence confirming or corroborating the effectiveness of such methods in boosting serotonin levels, relatively speaking undertaking such behaviours are unlikely to be detrimental.

Dangers of too much serotonin

Whilst it is important to try and raise serotonin levels when there are deficient, too much serotonin can have adverse and harmful effects. A key danger of too much serotonin is the development of serotonin syndrome.

Serotonin syndrome can occur when:

• Starting a new medication.
• Increasing the dosage of pre-existing medication.
• Exceeding the prescribed amount of medication.
• Taking additional medication, supplements or drugs that also affect serotonin.

Mild symptoms of serotonin syndrome include tremors, shivering, sweating, nausea, vomiting, restlessness and high blood pressure (hypertension). Meanwhile, severe symptoms include seizures, fainting, increased reflexed (hyperreflexia), muscle stiffness and twitches as well as abnormal heartbeat.

Overall, serotonin syndrome can be harmful and fatal under some circumstances, especially if it is severe and not detected or treated early on. Therefore, if you have any concerns regarding this then get in contact with a healthcare professional.

Summary

Serotonin is a key neurotransmitter and hormone that operates within the body to maintain normal and healthy functioning both physiologically and psychologically. Consequently, too little serotonin results in numerous consequences that individuals may find hard to manage, such as mental health problems. Therefore, certain measures can be taken to increase one’s serotonin levels, in particular individuals can alter their diet, supplement intake, medication usage and even adopt certain behaviours. Although, whilst this is an efficient way to increase serotonin levels, too much serotonin can lead to serotonin syndrome which can be injurious to one’s health. Overall, if you believe that the serotonin within your body is abnormal then consider consulting a healthcare professional for assistance.