Background

Tryptophan is an amino acid – one of the building blocks of protein. It is found in varying concentrations in a wide range of food proteins; however the highest concentrations are found in dried egg white and dried milk. Other food sources of tryptophan include turkey meat, oats and canned tuna1. Tryptophan is regarded as one of the Indispensable Amino Acids (IAA), also termed “essential” amino acids as they are amino acids that cannot be synthesised in the human body. There are other amino acids that are regarded as “non-essential” or Dispensable Amino Acids (DAA).

Much has been written regarding tryptophan in the diet of infants, particularly in terms of the levels in human milk. Tryptophan is regarded1,2,3  as a precursor for the synthesis of  neurotransmitters (serotonin and tryptamine) and, with its metabolites, has an effect on bodily functions such as appetite, sleeping / waking and also the perception of pain2. Melatonin is a hormone that is produced in the body as part of the “tryptophan/serotonin pathway”1 and regulates the patterns of sleep, among other bodily functions1,2. The highest level of melatonin in the body is associated with darkness at night and in healthy individuals reaches a peak at around 2am4. Sleep quality is associated with peak melatonin secretion and if this is delayed, sleep quality suffers4,5,6,.

The transport of tryptophan through cell membranes in the body can be inhibited by the presence of large neutral amino acids (LNAA)1,3. The LNAA are comprised of: tyrosine, phenylalanine, leucine, isoleucine and valine6. For tryptophan to be optimally available to the body, the ratio of the level of tryptophan to the level of LNAA (TRP/LNAA) must be carefully monitored and maintained at as high a level as possible6.

Levels of Tryptophan in the Diets of Adults

Typically, the level of tryptophan within the protein consumed by adults is low, relative to the level of other amino acids, particularly the other essential (indispensable) amino acids. Despite this, however, it has been estimated that the average intake of tryptophan in USA adults was 826mg/day7. This was in contrast to an Estimated Average Requirement (EAR) for tryptophan for adults in the USA of ~280mg for a 70kg adult7.

The EAR for protein in Australia and New Zealand is 37 – 46g /day (women) and 52 – 65g /day (men)8, with no specified requirements for any individual amino acids. Clearly the intake of protein (and therefore tryptophan) will vary both within a country, but also between countries, depending upon both total protein intake and the types of protein consumed. For the purposes of this discussion and in the absence of specific data for Australia and New Zealand, it has been assumed that the intake of tryptophan by adults in Australia and New Zealand is at similar levels to those in the USA.

The Effects of Supplementary Tryptophan in Adult Diets

The intake of supplementary tryptophan within the diet of an adult has been linked with improvements in sleep duration and depression symptoms7, reduction in cognitive decline, reduced risk of onset of diabetes, mediation of mood disorders9,10, as well as a number of other conditions1,9. The evidence for any specific cause and effect, linked with tryptophan intake, varies to some extent with the type of condition or disease, gender of the individual and the genotype of the individual10. It has been also noted that an intake of pure tryptophan “increases the release of several hormones including growth hormone, cortisol and prolactin”11. Taking this into account, the effects of supplementation of any specific amount of tryptophan for any individual may be difficult to predict. The addition of pure tryptophan to the diet of adults has been the subject of a number of studies, using supplementation levels of between 0.8g to 3.0g per day10. Several studies reported varying effects, depending upon genotype10, however they were regarded as safe9,10.

With regard to the markets of Australian and New Zealand, The consumption of pure tryptophan, in the form of a powder or tablet would be regulated at this time as a therapeutic good, rather than a food. No pure tryptophan therapeutic goods are marketed in Australia at this time.

The Effect of the Consumption of Tryptophan Rich Proteins

With regard to the increased consumption of tryptophan from nutrient rich foods, this has been studied using different proteins that contained relatively high levels of tryptophan9,10,11,13,14. The protein sources included α-lactalbumin, hydrolysed casein, hydrolysed egg white and sodium caseinate7,10,11,12,13. In these studies, specific quantities were added to the diets of adults to study the effects of increased intake of tryptophan and the effect of the TRP/LNAA ratio on the plasma level of tryptophan.

Whilst the intake of tryptophan can be increased by selecting a specific range of foods that have higher levels of tryptophan, there is also the consideration of the TRP/LNAA ratio. The absorption of tryptophan into the bloodstream (measured as ‘plasma tryptophan’10) is affected by the presence and level of LNAA6,10,11,12. The LNAA are preferentially absorbed to tryptophan and at high levels can block the absorption of tryptophan to some extent11,12. To ensure a relatively high level of tryptophan is achieved in the plasma, the ratio of the TRP/LNAA ratio needs to be controlled6,11,13. Studies indicate that a protein source with a TRP/LNAA ratio of 0.10 or higher may be more effective in achieving higher plasma tryptophan levels10,11,12,14,15,16.

In several studies in adults, the ratio of TRP/LNAA of above 0.07 in the protein of food was used, with a ratio of 0.10 being found to make a significant improvement in various aspects of mood (including depression, anger and tension)14,15,16. These studies used α-lactalbumin as a protein source, compared with another type of protein (casein). The TRP/LNAA ratio for α-lactalbumin was measured 0.087, whilst the ratio for casein was 0.04714,15,16. The plasma testing showed a TRP/LNAA ratio in the plasma of 0.104 for the α-lactalbumin and 0.071 for the casein. In a follow-up trial plasma testing showed a TRP/LNAA ratio of 0.104 after an α-lactalbumin diet and 0.073 after the control diet (casein)14,16.

The effect of the differing intakes of tryptophan from food in individuals has been linked to various behaviours and mood disorders16,17,18, particularly with older adults. This has been linked with “enhanced serotonin neurotransmission” that has a “widely acknowledged antidepressant function”11. Studies have indicated that people with mood disorders had a lower intake of tryptophan than those with higher intakes of tryptophan7,18. It has also been proposed that consuming a tryptophan enriched diet may assist with improvement in mood, sleep patterns, cognitive decline and resistance to type 2 diabetes9,10,11,12. Studies have indicated that intakes of as low as 2-4g of pure hydrolysed egg protein11,13 and 15g, 20g and 40g of α-lactalbumin have shown significant increases in plasma tryptophan14,15,16. The effects included improved cognitive performance, improved mood and well-being, including improved coping ability, lower anxiety and better sleep efficiency11,12,14,15,16.

Summary

The effects of increasing the consumption of tryptophan rich foods, such as eggs and milk products, particularly α-lactalbumin, have been studied over the past 20 years or more. The link between a higher level of plasma tryptophan and the higher level of serotonin in the body, have led to evidence of improved mood and well-being, including less anxiety, better cognitive ability and improved sleep. Whilst tryptophan intake can be increased by a simply higher protein diet, the key factor to increasing plasma tryptophan in the body is having protein sources that exhibit a high TRP/LNAA ratio, preferably greater than 0.10. 

Austral Foods has taken on these findings in development of their night formulation for adults to match what has shown to be efficacious in research – NiMera’s night drink has been developed to improve cognitive performance, improve mood and well-being and support better sleep efficiency of adults and children.

Based on Science

NiMera Night Sleep Drink Powder is a whey protein concentrate rich in alpha-lactalbumin which naturally contains high amounts of the serotonin precursor tryptophan. Increased dietary intake of tryptophan has documented beneficial effects on brain serotonin synthesis and activity with positive effects on mood, cognitive performance and improved sleep pattern. 

NiMera Night Sleep Powder Drink contains:

-Children 6-11 years

-5.6g α-lactalbumin and 180.9mg of tryptophan

-Children 12-17 years

-11.2g of α-lactalbumin and 363.9mg of tryptophan

-Adults 18 and over

-16.8g of α-lactalbumin and 544.8mg of tryptophan. 

Refer to the table for all the nutritional information.