Assessment of the intake of tryptophan-enriched cereals in the elderly and its influence on the sleep-wake circadian rhythm

Sleep-wake circadian rhythm disturbances are a common problem associated to aging. Although this problem can be caused by several factors, low levels of the indol melatonin are related with these alterations. Our aim was to evaluate if the consumption of cereals enriched with tryptophan, the precursor of both serotonin and melatonin, can enhance sleep problems in elderly people. Participants (n=12; aged 5567 yr) were selected from Elderly people Resumo Perturbações do ritmo de sono circadiano são um problema comum associado com o envelhecimento. Apesar deste poder ser causado por vários fatores, baixos níveis de melatonina indol estão relacionados com estas alterações. O nosso objetivo foi avaliar se a ingestão de cereais enriquecidos com triptofano, o percursor de serotonina e melatonina, pode melhorar os problemas de sono de pessoas de idade. Os participantes (n=12; com idades entre os 55 e 67 anos) foram selecionados da Univer-

Assessment of the intake of tryptophan-enriched cereals in the elderly and its influence on the sleep-wake circadian rhythm University of The University of Extremadura. During all the assay participants wore a wrist actimeter and they filled every week an STAI anxiety test. Data were collected following this schedule: Control week: participants ingested a control cereal both at breakfast and dinner (22.5 mg tryptophan/ 30g product per dose); Treatment Week: volunteers consumed a tryptophan enriched cereal both at breakfast and dinner (60mg tryptophan/ 30g product per dose); Post-treatment week: participants ingested their habitual diet. We observed a decrease in sleep latency (p<0.01), wake bouts (p>0.05) and sleep fragmentation (p<0.001); on the other hand, an increase in actual sleep time (p<0.01), sleep efficiency (p<0.01) and immobile time (p<0.01) were detected. With respect to the anxiety test, there was an improvement in the state of anxiety. In conclusion, through a tryptophanenriched diet age related sleep problems can be improved.

Introduction
Elderly people usually show poor nocturnal sleep (Yong-Lu et al., 2002) and about 30% of people over 50 years of age suffer from sleep problems like frequent nocturnal arousals, higher sleep latency and lower assumed sleep than mature people (Zhdanova et al., 2009). These alterations are associated with attention or memory difficulties, mood alterations and day-time sleepiness.
Tryptophan is an essential amino acid ( Figure 1) which is involved in sleep quality through its metabolites neurotransmitter serotonin and indol melatonin (Garrido et al., 2010;Cubero et al., 2011). It is well known that melatonin levels decreases in elderly people -it even can be absent - (Baskett et al., 2003). Sleep problems in old people may be caused by alterations in their tryptophan metabolism. Such alterations produce low levels of the neurotransmitter serotonin -its highest peak is produced at the end of light hours -and the hormone melatonin -which has its peak during dark hours through serotonin N-acetyltransferase activation (Hussain and Mitra, 2000). These molecules are involved in other processes like mood, depression, memory or attention (Silber and Schmitt, 2009).
It has been shown through tryptophan-enriched diets that both serotonin and melatonin levels can be increased, reducing sleep problems (Cubero et al., 2005). This may consequently improve sleep in the elderly. Our aim was to evaluate how tryptophan-enriched cereals (ORDESA S.L.) influence old peoples mood and sleep problems.

Materials and methods
Sample Participants (n=12) were volunteers aged between 55 and 67 (Table 1) years who suffered from sleep problems (more than three nocturnal awakenings or more than one hour to fall asleep). All volunteers were retired and women were post-menopausal. They were selected from Elderly People University of the University of Extremadura. Every volunteer consumed 30 g of tryptophan-enriched cereals (60 mg tryptophan) per dose for breakfast and dinner after a week consuming control cereals (22.5 mg tryptophan per 30 g dose). Finally, there was a post-treatment week with no cereals.

Measurement of sleep and anxiety
Sleep parameters were recorded by a wrist actimeter (Actiwatch©, Cambridge Neurotechnology Ltd, UK), which participants wore all time, and analyzed with Sleep Analysis 5© (Cambridge Neurotechnology Ltd, UK) software.
Before the study and during the study, on the last day of every experimental week at 10.00 a.m; volunteers filled an STAI (Spielberg et al., 2008) anxiety test. STAI results were expressed and related to a Spanish tipification (Urraca, 1981). This assay was carried out in October, 2010.

Statistics
Data are expressed as mean ± standard error and represented as fold-increase over control levels (expressed as 1).
Statistical analysis were performed with Graphpad Prism 5©; sleep parameters were analyzed by ANOVA test and anxiety parameters were analyzed with a Mann-Whitney U test. Significant level was established at p-value<0.05. Figures 2, 3, 5 and 6 show that after one week of tryptophan-enriched cereals ingestion both at breakfast and dinner (60 mg tryptophan/ 30 g product per dose) led to an increase in actual sleep time (p<0.01), sleep efficiency (p<0.01) and immobile time (p<0.01). In addition, figures 4, 7, 8 and 9 reveal that sleep efficiency, wake bouts and fragmentation index had lower values than in control week.        After participants ingested tryptophan-enriched cereals for one week there was a decrease in state of anxiety (Figure 10; p<0.05). However there were no changes in trait anxiety (Figure 11).

Figures 11 and 12.
Tryptophan enrichedcereal influence on State Trait Anxiety Inventory (STAI). Results are expressed related to a Spanish tipification. Each value represents mean ± SEM. *p<0.05 with respect to basal.

Discussion
The essential amino acid tryptophan has been reported as a molecule with sleep-enhancing properties which can improve sleep/wake cycle through its conversion into melatonin, which has a strong natural hypnotic effect (Garrido et al., 2009;Garrido et al., 2010;Bubenik and Konturek, 2011). It has been reported that some populations who suffer from sleep problems can improve their sleep through a tryptophan-enriched diet both animals or humans (Cubero et al., 2007;Cubero et al., 2009;Paredes et al., 2009).
After tryptophan administration serotonin and melatonin levels become higher (Sánchez et al., 2008). In this way, populations which present low melatonin or serotonin levels -like babies and elderly people -can have better levels of these molecules to improve their sleep/ wake cycle (Riemersma et al., 2005;Cubero et al., 2005).
It is well accepted that sleep problems have negative effects on mood, in fact, it has been extensively investigated with experimental models by tryptophan acute depletion (Silber and Schmitt, 2009). On the other hand, it has been reported that melatonin has a possible anti-depressive, anxiolytic, analgesic or sedative effects, among others, probably based on its effect on the circadian functions regulation (Hansen et al., 2011).

Conclusion
Tryptophan-enriched cereals improved actual sleep time, sleep efficiency, immobile time, sleep latency, wake bouts and fragmentation index in the  volunteers of this sample. Also, this kind of diet improved aspects of anxiety-like trait or state during the treatment week, enhancing the volunteers' mood.
These findings suggest that the intake of tryptophan-enriched cereals exert positive effects on the sleep of elderly with sleep problems and they may, therefore, represent an alternative to treatments based on pharmacological drugs.