Serotonin 101: All You Need to Know To Manage ItJan 16, 2023
Article by: Inka Land, neuropsychology MSc
This science-based article tells you all you need to know about the neurotransmitter serotonin and how to boost its levels naturally.
Table Of Contents:
1. What is serotonin
2. What does serotonin do
3. Serotonergic system / serotonin pathway
4. Serotonin receptors
5. When is serotonin released
6. LOW serotonin symptoms
7. HIGH serotonin: SEROTONIN SYNDROME
8. How to boost serotonin naturally
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What is serotonin
Serotonin, also known as 5-HT, is a neurotransmitter and neuromodulator in the brain and is mainly known for its importance for cognition, mood, social connection, and sleep. It also affects personality traits and stress resilience.
Serotonin is also a gut hormone but this article focuses on the brain and the central nervous system.
What does serotonin do?
Serotonin affects cognition, mood, and physiology – pretty much all aspects of health including emotional health, regulating metabolism and digestion, and improving sleep quality. Here are 6 well-studied important roles of serotonin.
1. Serotonin improves mood and lowers anxiety
Serotonin facilitates feelings of positivity, especially calm types of positive emotions like the feeling of contentment and general well-being. Serotonin appears to have mainly inhibitory and calming effects on higher brain regions, unlike dopamine and noradrenaline, which are increasing alertness and arousal.
2. Serotonin improves sleep
Serotonin is important for the regulation of sleep. However, it’s not simply making you sleepier. In fact, during the day, serotonin increase wakefulness which is important for the sleep onset later in the evening. Serotonin levels seem to be important for sleep quality, especially slow-wave sleep also called deep sleep.
Serotonin is also the precursor of melatonin – the most known sleep onset hormone in the brain. Therefore, serotonin participates in regulating circadian rhythm, and it especially supports sleep onset. Melatonin production is facilitated by some vitamins including zinc, magnesium, b vitamins, and folate.
3. Serotonin participates in forming long-term memories
Serotonin modulates brain processes involved in memory. For example, there are a lot of serotonin receptors in the brain’s hippocampus which is known to form long-term memories and aid learning. Increases in serotonin signaling upregulate especially dentate gyrus – whose role in memory formation has been found to be central.
4. Serotonin reduces hunger
Serotonin is important for controlling and suppressing appetite. For example, even a small carbohydrate-containing snack can put break into hunger because it increases serotonin – a natural appetite suppressor. Studies have found at least three different serotonin receptors are central to the feeling of satiety Due to this, some recently approved anti-obesity drugs work by increasing serotonin.
5. Serotonin reduces pain
Serotonin is one of the most known pain-suppressing neurotransmitters. In studies, where participants’ serotonin levels are lowered, their pain perception lowers. The exact mechanism of how serotonin regulates pain is not completely clear between serotonin and pain reduction. That’s one reason why SSRIs, drugs that increase the availability of serotonin, are used to treat some pain conditions like migraines, IBS, and fibromyalgia.
6. Serotonin controls body temperature and breathing
Serotonin also helps control basic bodily functions like body temperature and breathing. For example, One study showed that serotonin-deficient mice had lower body temperature in a cold room when normal serotonin-producing mice were able to regulate core body temperature higher in a cold room. Serotonin also helps regulate the rhythmic patterns of breathing.
7. Serotonin is linked to addiction and withdrawal symptoms
A neurotransmitter that’s often linked to addiction is dopamine. However, many don’t know that also serotonin plays role in addictions. Many addictive substances like opioids and alcohols increase serotonin and when during withdrawal the drop in serotonin can cause anxiety, nervousness, and sadness. This may make the person seek behaviors that increase serotonin again – like the substance one is trying to avoid.
Even a single dose of alcohol can actually change the functioning of the serotonergic system and long-lasting use causes changes in the whole system and the brain’s ability to respond to serotonin.
In the brain, serotonin works in the serotonergic system. It originates from the raphe nuclei, where serotonin is produced. From here, there are pathways to virtually all brain areas which explains its wide-ranging effects on cognition, behaviors, and even basic physiology.
Currently, we know 14 types of main serotonin receptors: 5 HT 1-7 and their subreceptors (5HT1A, 5HT1B, and so on). See the image for clarity.
Their functions are complex, so I won’t go into details here. They have different functions in the brain, some excite nerve cells and others inhibit them. For example, types 1 and 5 usually inhibit target receptors and the rest are excitatory. You can see some of the qualities in the image above that are from a research article.
How is brain serotonin produced?
Brain serotonin is produced from the amino acid tryptophan that you get from foods like protein, oat, and bananas.
Image copyright: Inka Land
First, the tryptophan travels to the brain through the blood-brain barrier. It’s the only serotonin precursor that can cross the blood-brain barrier, and therefore the intake of tryptophan is essential for serotonin production.
In the brain, enzymes convert tryptophan into 5-HTP and 5-HTP into serotonin. The serotonin is stored in vesicles of the brain cells for later release. See the images.
Some things can lower brain serotonin production by affecting the efficacy of the conversion
- Too little tryptophan from the diet: not enough building blocks
- Too much brain dopamine: blocks the hydroxylation of tryptophan
- Stress and inflammation: moves tryptophan to kynurenine pathway instead
- Gut dysbiosis or lack of good gut bacteria
When is serotonin released?
Serotonin is released from the vesicles when the serotonergic cells are stimulated. Many behaviours stimulate serotonin release, like exercise, carbohydrates, sunlight, socializing, and positive experiences.
Importantly, after the release, serotonin is reuptaken (absorbed back) into the presynaptic neuron by Serotonin reuptake transporters (SERT) or broken down by an enzyme, mainly Monoamine oxidase (MAO). The degradation and uptake also partially affect how much serotonin there is affecting the brain. For example, common antidepressant drugs like SSRI work by inhibiting the reuptake of serotonin which leaves more serotonin stimulating the receptors.
Low serotonin symptoms
Low serotonin is usually linked to depression, sleep issues, and irritability.
Symptoms of low serotonin
- Sadness and mood issues
- Lack of Deep Sleep / slow wave sleep
- Problems falling asleep
- Circadian disturbances
- Digestive problems
- Post-Traumatic Stress Disorder
- Panic Disorder
- Disagreeable behavior
- Feeling of loneliness
High serotonin symptoms / Serotonin syndrome
Too high serotonin levels are not particularly good either. Although high normal levels of serotonin have a positive effect on mood, sleep, and sociability, abnormally high levels can lead to serotonin syndrome.
Serotonin syndrome is caused by the over-activity of serotonergic synapses. This can be caused because of multiple things like taking too many serotonergic drugs, antidepressants, or serotonergic psychedelics; inhibition of serotonin uptake; slower serotonin degradation; increased serotonin synthesis; increased serotonin release; and activation of serotonergic receptors.
Although there is no single receptor responsible for this, it appears that at least 5HT2a receptors play a key role in the severe symptoms of serotonin syndrome.
The symptoms include shivering, sweating, confusion, restlessness, high blood pressure, muscle twitches, fewer, seizures, and fainting. It can be dangerous but it’s very rare and usually include misuse of medications or psychedelics.
How to boost serotonin naturally?
There are many scientific ways to increase serotonin levels naturally without medicines.
1. Eat tryptophan-containing foods
To boost serotonin, you need serotonin precursors from the diet. High tryptophan foods include chicken, turkey, dairy, oat, banana, kiwi, dates, and pumpkin seeds.
Also high-carb, low-protein meals boost serotonin. This is because other amino acids from proteins lower tryptophan’s transport to the brain. Carbohydrates help to shuffle other amino acids into muscles and organs because they raise insulin. Insulin activates the transport of amino acids into muscles. As other amino acids get pushed into muscles, tryptophan stays in the bloodstream and is directed to the brain and converted to serotonin in the brain.
2. Try L-Tryptophan supplement
A systematic review concluded that an L-tryptophan supplement between 0.14 and 3 g daily may improve mood and other studies link this to better sleep onset. Animal studies show that brain serotonin is directly linked to the availability of tryptophan in the bloodstream.
N.B. If you are on medication that affects serotonin, then talk to your healthcare provider before trying it.
3. Exercise to increase serotonin
Several studies suggest that exercise can increase serotonergic activity in the brain. This might be because of the stimulation of the serotonergic brain cells and because of the improved tryptophan transport to the brain. Tryptophan get’s easier access to the brain after exercise because it clears out some competing amino acids, like BCAA’s from the bloodstream to the muscles.
4. Avoid overstimulating dopamine
In the brain conversion of serotonin, the slowest (rate-limiting) step is the hydroxylation of tryptophan in 5-HTP. And this process can be inhibited with high amounts of dopamine. Therefore, it’s important that these neurotransmitters are in balance.
5. Manage stress
There are two pathways that use tryptophan: the serotonin production pathway and the kynurenine pathway whose role is to produce NAD+ for counteracting inflammation and stress. Therefore, high amounts of inflammation and stress move more tryptophan into the kynurenine pathway instead of serotonin production. Managing stress and lowering inflammation will therefore help with serotonin production.
6. Practice positive thinking and visualization
So the link between serotonin and mood could be a 2-way road. This means that not only increased serotonin leads to a better mood but also positive mood can increase serotonin synthesis in the brain. For example, when people are asked to recall a positive life event, serotonin synthesis increases compared to recalling sad or neutral emotional events. So imagining and visualizing positive things, doing Loving-Kindness meditation, or writing a journal where you list 3 good things that happened today may increase serotonin.
Serotonin is a neurotransmitter important for mood, sleep, memory, weight management, metabolism, and basic bodily functions.
It’s made from dietary tryptophan found in protein-rich foods, bananas, oat, pumpkin seeds, and some fruits. Tryptophan transport in the brain is enhanced by eating carbohydrate-rich (low-protein) meals because it helps to transport other amino acids in the muscles and therefore tryptophan gets easier access to the brain. Make sure to still get your complete proteins and essential amino acids.
Natural ways to boost serotonin are: tryptophan, L-tryptophan, exercise, sunlight exposure, bright light exposure, positive thinking, controlling dopamine, and reducing inflammation and stress.
Too low serotonin may lead to depression, irritability, psychiatric conditions, or sleep problems. Too high serotonin may lead to serotonin syndrome, but it’s very rare and usually caused by the use of serotonergic drugs or psychedelics.
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