Why Does Tryptophan Make You Sleepy?

When you think about tryptophan, what’s the first thing that comes to mind…

Turkey?

We knew it.

Most people think that the turkey feast you have on Thanksgiving and the severe fatigue that follows is due to the presence of tryptopha...

...but that may not actually be what’s causing you to be in that so-called “food coma.”

Turkey contains tryptophan, but not enough to induce that level of fatigue. But that’s beside the point.

What you’re likely dying to know is why tryptophan makes you sleepy, so we’re going to tell you...

But before we do that, let’s understand what tryptophan is and how it relates to sleep.

Tryptophan and its Link With Sleep

Tryptophan is an essential amino acid; recall that essential means your body can’t produce is, so it must be obtained through either diet (food sources) or supplements.

As an essential amino acid, tryptophan is one of the building blocks for the biosynthesis of proteins.

But it also serves as a precursor for the synthesis of other important biological compounds like melatonin, 5-HT, kynurenin (KYN), indole-3-acetic acid (IAA), and the vitamin niacin (B3) .

Here’s where sleep comes in

With tryptophan, specifically, once absorbed into the blood stream, it goes on to make a compound called 5-hydroxytryptophan, or 5-HTP for short.

5-HTP is then converted into serotonin, and finally melatonin—although that’s a much simpler explanation that what actually happens, of course.

Related Post: L-tryptophan vs. 5-HTP: Which is Better?

And the final product of that pathway, melatonin, is where sleep enters the picture.

Behind the Scenes of Sleep

Have you ever noticed that when it starts to get dark out, your body seems to slow down and you’re ready to hit the sheets?

That’s because of something called your circadian rhythm, or your sleep-wake cycle, which is governed by a hormone called melatonin.

Quick Explanation of Melatonin

Melatonin is secreted by the pineal gland, a tiny pea-sized gland in the center of your brain. 

It follows a 24-hour bio rhythm, whereby levels are at their highest in the evening hours when its dark and gradually fall to their lowest in the morning.

And for those of us who want to geek out a bit more, melatonin and cortisol generally work on opposite rhythms: 

• Cortisol increases during the day to keep you awake and alert.
• Melatonin decreases to suppress sleep, and vice versa. 

This is why during daytime hours melatonin levels fall; cortisol increases to keep us stimulated, but when cortisol levels naturally start to fall towards the evening, melatonin secretion increases to induce sleep.

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For most of us—or at least those of us who aren’t severe night owls—our sleep-wake cycle follows that of the sun.

To be specific, the secretion of melatonin is regulated by a rhythm-generating system located in the suprachiasmatic nucleus, a region of the hypothalamus, which itself is regulated by light . 

When light enters our eyes, melatonin production dwindles to signal that it’s time to wake up.

Trytophan's Link to Melatonin

When the pineal gland is not synthesizing melatonin (it does so primarily at night), L-tryptophan is converted to melatonin in the gut (primarily during the day because pineal synthesis of melatonin is inhibited).

This is a good thing because if the pineal was spitting out melatonin all day every day, chances are you would probably be having Netflix and chill days more than you’d like.

With all of that said, the point is for you to understand that melatonin is the hormone that controls our sleep-wake cycle and induces sleep by binding to specific receptors in the brain that reduce nervous system activity.

Why Should You Care About Melatonin & Tryptophan?

Because if your body isn’t producing enough melatonin on its own, you can help it along by eating tryptophan-rich foods or supplementing with tryptophan.

But it’s also important to note that dietary tryptophan isn’t as well absorbed as supplemental sources. That’s because in order to cross the blood-brain barrier (BBB), it has to hitch a ride with a specialized transport proteins.

Think of it this way: it’s 11:30pm and the last bus home is about to arrive, but you’re surrounded by 5 other burly men that you can’t really overpower to get one of those 5 places.

And when it comes time to getting on that transport protein and catching a ride to the brain, you’re competing with those men (i.e. larger amino acids like like valine, isoleucine, leucine, tyrosine, phenylalanine, and methionine) to make it on .

Because those men obviously have a bit more of a presence than you (tryptophan), it makes it a bit tough for tryptophan to get into the brain.

The level of absorption is therefore dependent on the ratio of tryptophan to other amino acids.

Less amino acids to compete with means more tryptophan crosses the blood-brain barrier, leading to a potentially higher conversion rate to melatonin.

However, the reality is that food sources don’t just contain tryptophan, so it’s a constant competition for who’s going to catch the ride on the transporters.

That not it, though.

Part of the reason why tryptophan induces such a wave of fatigue is also partly due to insulin.

When you eat foods that are high in carbs, your insulin levels spike, and insulin is the hormone that makes glucose and most amino acids available to tissues.

• Q: But insulin doesn’t really seem to bother with tryptophan… why, you may ask? 
• A: Because most of the tryptophan in the blood is bound to the protein albumin, making in unavailable to tissues—besides the brain, of course. When it’s unavailable for insulin to bind with, insulin binds to the other amino acids floating around in the blood.

Get where we’re going with this?

When there isn’t so much competition for tryptophan, it makes it easier for tryptophan to cross the blood-brain barrier.

But hold on a minute… there’s another part.

Even though tryptophan can cross the blood-brain barrier, that doesn’t give it the right of way into melatonin.

The pineal gland (remember that guy?) has ready access to all of the tryptophan floating around in the blood. But rather than making melatonin, it makes serotonin—hence why you feel happy after eating a mass amount of turkey.

The rate of melatonin synthesis is instead controlled by the number of two specific enzymes available to convert that serotonin into melatonin:

1. Arylalkylamine N acetyltransferase (AANAT)
2. Hydroxyl-indole-O-methyltransferase (HIOMT) .

And funny enough, the levels of these enzymes spike once it turns dark due to enhanced release of norepinephrine from neurons terminating on pineal cells.

The sources of Tryptophan can affects its overall effectiveness of inducing sleep

Taking all that into consideration, there’s no denying that tryptophan plays an important role in melatonin synthesis, but it’s important to consider where you’re getting your tryptophan from.

Is it a sole amino acid (such as in Performance Lab Sleep) where competition is minimal and it can be converted right away, or is it food sources where there’s lots of competition and little opportunity for conversion?

So, if you’re looking to tryptophan to help induce sleep, choose wisely, my friends.