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.

IntroductionBasal insulin should be injected at the same time each day, but people with diabetes sometimes mistime their injections. It is not known whether irregular daily dose timing affects diabetes-related factors. We report here our evaluation of the effects of deviations from a regular dosing schedule on glycemic control and hypoglycemia on patients treated with long-acting insulin (insulin glargine U100). We also consider the effects of ultra-long-acting insulin (insulin degludec) in this context.MethodsNineteen individuals with type 1 diabetes and 58 with type 2 diabetes were enrolled. Demographic data on all participants were retrieved from their medical records. Variation in dose timing was determined as the difference between the time of the earliest mistimed dose and the time of the latest mistimed dose, for each participant, over a 2-week period. All participants completed the Summary of Diabetes Self-Care Activities questionnaire, Problem Areas in Diabetes scale and 5-Item World Health Organization Well-being Index. Glargine U100 was switched to degludec in those individuals with type 2 diabetes who achieved inadequate glycemic control or suffered from frequent hypoglycemic episodes or who required two injections per day, and changes in hemoglobin A1c level and frequency of hypoglycemic episodes during the 12-week period were compared.ResultsA greater difference in dose timing was related to a higher frequency of hypoglycemic episodes and overweight in persons with type 2 diabetes. Smoking, drinking and living alone were independently associated with a greater difference in dose timing. Insulin degludec decreased the frequency of hypoglycemia and improved glycemic control in participants whose dose mistiming was >120 min.ConclusionFixed dose timing should be employed for basal insulin, as a larger difference in dose timing worsens diabetes-related factors. Insulin degludec improved glycemic control and lowered the hypoglycemia rate in persons with more irregular dose timing.