Tryptophan – Does it Work as a Calmer?

Tryptophan has recently had a large amount of bad press as regards its use as a calmer for horses. For example, a friend recently sent me this review of L-Tryptophan as a calmer for horses:

Although I think this article is very well researched (and the authors must’ve spent weeks gathering all this info together), I do disagree fundamentally on some of its points.

Firstly, a bit of background information. This is how Tryptophan (an essential amino acid) works:

Tryptophan >>>>>> 5-Hydroxytryptophan (5-HTP) >>>>>>>>Serotonin

Tryptophan is converted into 5-HTP which passes into the brain and is then converted into Serotonin, the calm and happy neurotransmitter. ☺

The article that I was sent pointed out that:

  1. There are zero studies that confirm Tryptophan as a calmer in horses. This is true. It is also true of a huge number of other nutraceuticals. Research into naturally occurring, easily available ingredients is limited, because of the lack of financial return to big pharmaceuticals. Especially in horses. It doesn’t mean that Tryptophan isn’t a valid calmer.
  1. Of the work that has been done, very low doses of Tryptophan (25 and 50mg per day) cause mild excitement. (Bagshaw study.) As mentioned in the article, this study was very flawed. Only a few horses, only a few hours, too low a dose, breed differences. IMHO the poor horses probably just got a bit bored of standing around having their heart rate measured. I think this dose of Tryptophan did absolutely nothing.
  1. Very high oral doses (350 and 600mg/kg bodyweight) lead to anaemia, increased respiration and haemolysis. This also doesn’t mean that Tryptophan doesn’t work as a calmer. It just means that very high doses are dangerous. Very high doses of carrots are also dangerous. That doesn’t mean that it is bad to feed horses carrots.

(Note: The daily dose of Tryptophan included in our Calm mix is 2000 mg per day. This is above the dose that Bagshaw found to cause slight excitement (25 or 50mg per day) and way below the dose that Paradis found to cause anaemia (175 000 mg or 300 000 mg per day).)

  1. They then make the point that other factors (diet, exercise, gender etc.) influence the uptake of Tryptophan and therefore the effectiveness.  This is also true (in fact I think it’s a bit of a no-brainer), but also doesn’t mean that Tryptophan doesn’t work.
  1. The one point they make which is that Tryptophan might decrease endurance is valid.  But I guess if you have a horse that leaps around like a maniac for half of the endurance ride, that might also decrease his ability to stay the distance. It’s a judgement call.
  1. Then there is the also very valid point that excitability in horses is not exactly well defined. Is it hysteria? Or aggression? Or hyperactivity? Or fearfulness? Because Tryptophan seems (in studies in other species) to have varying effectiveness in controlling these varied symptoms. Aggression, fearfulness and hysteria are decreased by Tryptophan. Whereas hyperactivity isn’t.

The one symptom which has strongly been shown to improve with Tryptophan supplementation in other species is depression. Which these authors immediately disregarded because they felt it was irrelevant to horses. I disagree. I think horses can and do get depressed. And that anything that improves mood is bound (IMHO) to improve behaviour.

One possible reason for Tryptophan sometimes not performing ideally as a calmer is due to a liver enzyme called Tryptophan pyrrolase. This enzyme breaks Tryptophan down, rendering it inactive. It is known to be activated by an increased concentration of Tryptophan in the horse’s system.  So, the more Tryptophan is present, the more it is broken down by the enzyme.

In our Calm mix, we have neatly bypassed this phenomenon by adding Vitamin D3. In a very recent Screen Shot 2015-08-15 at 15.35.06study, Vitamin D3 has been found to increase the production of the enzyme Tryptophan Hydroxylase 2. This is the enzyme which drives the conversion of Tryptophan to 5-HTP, which in turn is converted to Serotonin. The conversion of Tryptophan to 5-HTP is the rate limiting step (slows the whole process down). So anything that can increase this step is invaluable in getting a higher Serotonin level into your horse’s brain.  And, more importantly, it mops up the spare Tryptophan sitting around so you don’t have the elevated level of Tryptophan activating its own breakdown. Clever, hey?

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