What is L-tryptophan?

L-tryptophan is an essential amino acid, most commonly known as the precursor to serotonin (which lifts our mood)[1].

What is L-tryptophan found in?

Food sources of tryptophan include oats, bananas, milk, tuna, chicken, turkey, peanuts, chocolate, and cheese [2]. Please be aware, however, that L-tryptophan needs adequate amounts of the co-factor B6 to convert to serotonin and this is important when thinking about supplementing with this amino acid.

What are the benefits of L-tryptophan?

Serotonin and melatonin production for good mood and sleep

The benefits of L-tryptophan come from the way it is metabolised in the body. L-tryptophan can go down a couple of different pathways, one of which is where the tryptophan- is converted to 5-HTP, then serotonin (which makes us feel happy), then melatonin (which makes us feel sleepy).

What can go wrong?

Tryptophan tends to be favoured down the kynurenine pathway when there is inflammation, high cortisol, genetic factors at play[3]
or if the body needs to make more niacin (vitamin in B3). So, when the kynurenine pathway is chosen, this often negatively impacts upon the amount of serotonin and melatonin made. Therefore, it is important to ensure a good intake of magnesium and B vitamins, as well as reducing stress wherever possible in order to get the best out of tryptophan.

Serotonin and depression, what's the link?

Due to the link between low serotonin with depression and anxiety, tryptophan is often studied for its ability to elevate mood[4]. As discussed above, it is important to encourage L-tryptophan down the 5-HTP pathway rather than the kynurenine pathway to get the mood enhancing effects of tryptophan[5]. This pathway also relies on the presence of other nutrients, notably magnesium and vitamin B6.

Tryptophan can also compete with other amino acids for absorption, it is therefore suggested to take tryptophan away from other proteins to maximise its serotonin potential.

Serotonin converts to melatonin, which is our sleep hormone and is important when it comes to getting a good quality night’s sleep. Traditionally, studies looking at tryptophan and sleep have typically used high doses of tryptophan and it has shown positive results.

What does the research say?

Let's take a look at a study that decided to test tryptophan using low doses.

One gram of L-tryptophan significantly reduced sleep latency and lower doses produced a trend in the same direction. Stage IV sleep was significantly increased by using 1/4 g of L-tryptophan[6]. These are amounts which we can typically get from diet alone. However, it is worth considering that in the presence of high stress, inflammation or genetic factors, higher doses achieved through supplementation may be a very helpful to get around these issues .