Abstract
BackgroundThe purpose of the present study is to investigate effects of tryptophan intake and light exposure on melatonin secretion and sleep by modifying tryptophan ingestion at breakfast and light exposure during the daytime, and measuring sleep quality (by using actigraphy and the OSA sleep inventory) and melatonin secretion at night.MethodsThirty three male University students (mean ± SD age: 22 ± 3.1 years) completed the experiments lasting 5 days and 4 nights. The subjects were randomly divided into four groups: Poor*Dim (n = 10), meaning a tryptophan-poor breakfast (55 mg/meal) in the morning and dim light environment (<50 lx) during the daytime; Rich*Dim (n = 7), tryptophan-rich breakfast (476 mg/meal) and dim light environment; Poor*Bright (n = 9), tryptophan-poor breakfast and bright light environment (>5,000 lx); and Rich*Bright (n = 7), tryptophan-rich breakfast and bright light.ResultsSaliva melatonin concentrations on the fourth day were significantly lower than on the first day in the Poor*Dim group, whereas they were higher on the fourth day in the Rich*Bright group. Creatinine-adjusted melatonin in urine showed the same direction as saliva melatonin concentrations. These results indicate that the combination of a tryptophan-rich breakfast and bright light exposure during the daytime could promote melatonin secretion at night; further, the observations that the Rich*Bright group had higher melatonin concentrations than the Rich*Dim group, despite no significant differences being observed between the Poor*Dim and Rich*Dim groups nor the Poor*Bright and Rich*Bright groups, suggest that bright light exposure in the daytime is an important contributor to raised melatonin levels in the evening.ConclusionsThis study is the first to report the quantitative effects of changed tryptophan intake at breakfast combined with daytime light exposure on melatonin secretion and sleep quality. Evening saliva melatonin secretion changed significantly and indicated that a tryptophan-rich breakfast and bright light exposure during the daytime promoted melatonin secretion at this time.
Highlights
The purpose of the present study is to investigate effects of tryptophan intake and light exposure on melatonin secretion and sleep by modifying tryptophan ingestion at breakfast and light exposure during the daytime, and measuring sleep quality and melatonin secretion at night
The sleepiness score was 27.3 ± 1.0 on the second day and 29.3 ± 1.0 on the fifth day, and the worries score was 27.7 ± 0.9 on the second day and 30.2 ± 1.0 on the fifth day, which means that sleep quality was better and they were less worried on the fifth day compared to the second
There were no significant differences between the scores on days 2 and 5, in Rich*Bright, the mean scores of sleepiness, sleep maintenance, worries, integrated sleep feeling, and sleep initiation on day 5 were higher than on day 2
Summary
The purpose of the present study is to investigate effects of tryptophan intake and light exposure on melatonin secretion and sleep by modifying tryptophan ingestion at breakfast and light exposure during the daytime, and measuring sleep quality (by using actigraphy and the OSA sleep inventory) and melatonin secretion at night. Exposure to light resets the phase of the clock in the suprachiasmatic nucleus [1]. Tryptophan is one of the essential amino acids and is contained in proteins sourced from milk, eggs, meat, grains, and beans. It can cross the blood–brain barrier and is transformed into serotonin in the brain, subsequently converted to melatonin. Zawilska et al reported that arylalkylamine N-acetyltransferase activity is affected by light; its activity declines in the photoperiod (while melatonin secretion decreases) and increases in the scotoperiod (when melatonin secretion increases) [11]. Tryptophan intake and the timing of light exposure must be considered together if the effect of tryptophan upon melatonin secretion and sleep quality is to be maximized
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