Urinary aMT6s Levels Research Articles

Association between nocturnal light exposure and melatonin in humans: a meta-analysis.

Night shift workers are more susceptible to circadian rhythm disturbances due to their prolonged exposure to nighttime light. This exposure during abnormal periods causes inappropriate suppression of melatonin synthesis and secretion in the pineal gland, thereby disrupting circadian rhythms. While it is believed that nocturnal light exposure is involved in suppressing melatonin secretion, research findings in this area have been inconsistent. Thirteen publications retrieved from PubMed and Web of Science databases were included to compare the differences between night shift workers and controls using aggregated mean differences (MD) and 95% confidence intervals (CI). After a comprehensive review, 13 publications were included and data on urinary melatonin metabolite 6-sulfameoxymelatonin(aMT6s) were collected for meta-analysis. The results showed that the morning urinary aMT6s levels were significantly lower in the exposed group than in the non-exposed group (MD = -3.69, 95%CI = (-5.41, -1.98), P < 0.0001), with no significant heterogeneity among the original studies (I2 = 42%, P = 0.13). In addition, night shift workers had significantly lower mean levels of 24-h urinary aMT6s than day shift workers (MD = -3.38, 95%CI = (-4.27, -2.49), P < 0.00001, I2 = 0). Nocturnal light was correlated with nocturnal urine aMT6s secretion and inhibited nocturnal aMT6s secretion (MD = -11.68, 95%CI = (-15.70, -7.67), P < 0.00001, I2 = 0). Additionally, nocturnal light inhibited the secretion of melatonin in the blood, with no significant heterogeneity between studies (MD = -11.37, 95%CI = (-15.41, -7.33), P < 0.00001, I2 = 0). The findings of this study indicate that exposure to nocturnal light among night shift workers leads to inhibition of melatonin secretion.

Subchronic Low-Dose Methylmercury Exposure Accelerated Cerebral Telomere Shortening in Relevant with Declined Urinary aMT6s Level in Rats

Methylmercury (MeHg) is a global pollutant with established toxic effects on the central nervous system (CNS). However, early events and early-warning biomarkers of CNS damage following exposure to low-dose MeHg are still lacking. This study aimed to investigate whether subchronic low-dose MeHg exposure had adverse effects on the cerebral telomere length, as well as serum melatonin and its urinary metabolite 6-sulfatoxymelatonin (aMT6s) in rats. Sixteen male Sprague Dawley rats were divided into two groups. Group I was the control group. In group II, rats were exposed to MeHg by gavage at a dose of 0.1 mg/kg/day for 3 months. This study revealed that MeHg exposure resulted in impairment of learning and memory ability, a slightly reduced number of neurons and an irregular arrangement of neurons in the hippocampus. It also significantly accelerated telomere shortening in the cerebral cortex, hippocampus and hypothalamus. Moreover, MeHg exposure decreased the levels of melatonin in serum and aMT6s in urine, partly by suppressing the synthesis of 5-hydroxytryptamine (5-HT) in the brain but promoted the expression of melatonin-catalyzing AANAT and ASMT. Importantly, cerebral telomere length was positively correlated with MT and aMT6s after MeHg exposure. These results suggested that the shortened telomere length in the brain may be an early event in MeHg-induced CNS toxicity, and the level of aMT6s in urine may serve as an early-warning biomarker for MeHg-induced CNS damage.

Dietary supplement of tomato can accelerate urinary aMT6s level and improve sleep quality in obese postmenopausal women

The aim of this study was to investigate the effect of the ingestion of tomato before bed on obese postmenopausal women's urinary 6-sulphatoxymelatonin (aMT6s) level and sleep quality. We quantified melatonin concentrations in beefsteak tomato, black tomato, and two commercial tomato juices and found that beefsteak tomato contained the highest level of melatonin. In this 8-week open-label, randomized controlled dietary intervention trial, 36 subjects completed the entire trial. The tomato group ate 250g of beefsteak tomatoes 2h before sleep for 8 weeks. Blood and urine samples were collected at the baseline and in the 8th week and were analyzed. The Pittsburgh Sleep Quality Index (PSQI) in the tomato group significantly decreased with time (p for trend=0.0297). After 8 weeks of the beefsteak intervention, all components of the PSQI in tomato group had significantly improved, and their aMT6s level was 10-fold significantly higher than that of the control group. Therefore, supplementation with beefsteak tomato before sleep can increase circulating melatonin and improve sleep quality in obese postmenopausal women.

Salt Loading Aggravates the Relationship between Melatonin and Proteinuria in Patients with Chronic Kidney Disease.

Objective Salt loading induces renal damage independently of blood pressure (BP) elevation via reactive oxygen species and sympathetic activity. Melatonin, a hormone that regulates the circadian rhythm, has multiple functions, including anti-oxidant effects and the inhibition of sympathetic activity. We have shown that impaired melatonin secretion is associated with renal damage in chronic kidney disease (CKD) patients. However, the associations between salt loading, melatonin secretion, and urinary albumin and protein have not been clarified. Methods We recruited 32 CKD patients, conducted 24-hour ambulatory BP monitoring and collected daytime and nighttime urine while the patients were consuming a standard salt (10 g/day) or low salt (6 g/day) diet. The excretion levels of albumin, protein and 6-sulfatoxymelatonin (aMT6s), a metabolite of melatonin, in daytime and nighttime urine were investigated in patients consuming standard salt and low salt diets. Results The urinary aMT6s levels in daytime and nighttime of the patients consuming standard salt and low salt diets did not differ to a statistically significant extent. However, the urinary aMT6s levels in patients consuming a standard salt diet-but not patients consuming a low salt diet-were significantly and negatively correlated with the daytime and nighttime urinary albumin and protein levels. Contrarily, no significant correlations were found between the urinary aMT6s levels and the BP levels, renal function, and plasma angiotensin II levels in patients consuming either a standard salt or low salt diet. A multiple regression analysis adjusted for age, sex, and body mass index revealed that the urinary albumin and protein levels were significantly and negatively associated with the urinary aMT6s levels in patients consuming a standard salt diet, but not in patients consuming a low salt diet. Conclusion Salt loading aggravates the relationship between melatonin secretion and albuminuria or proteinuria.

Melatonin Levels in Patients With Primary Open-angle Glaucoma With High or Low Intraocular Pressure.

To evaluate circulatory melatonin levels by assessing nocturnal urinary excretion of 6-sulfatoxymelatonin (aMT6s) in patients with primary open-angle glaucoma (POAG) and to compare the high-tension group and the low-tension group. This study included 80 eyes of 41 POAG patients and 87 eyes of 44 control subjects. POAG group was further classified into high-tension group and low-tension group according to the pretreatment intraocular pressure (IOP). The first urine in the morning was collected and aMT6s were measured using a commercial ELISA kit. Urinary aMT6s levels were expressed as ng aMT6s/mg creatinine. Differences in melatonin levels among the control and POAG subgroups were evaluated by generalized estimating equation adjusting age, sex, sleep duration, and intereye correlation. Urinary aMT6s/creatinine ratio did not differ between POAG and control group (P=0.097). The difference in the aMT6s/creatinine ratio between the 3 groups-high-tension group with baseline IOP≥21 mm Hg (19.74±3.12 ng/mg), low-tension glaucoma group with baseline IOP<21 mm Hg (26.71±3.47 ng/mg), and control group (30.35±3.05 ng/mg)-was statistically significant (P=0.046). Post hoc analysis revealed that the difference between the control and high-tension glaucoma groups was significant (P=0.014), whereas the difference between the control and low-tension glaucoma groups was not (P=0.436). This study found low melatonin levels in high-tension glaucoma compared with the control.

Urinary 6-sulfatoxymelatonin level and breast cancer risk: systematic review and meta-analysis

6-Sulfatoxymelatonin (aMT6s) is the main metabolite of melatonin in urine, and is a reliable surrogate biomarker reflecting the blood melatonin concentration. This meta-analysis assessed the association between urinary aMT6s level and BC incidence. The electronic databases PubMed, EMBASE, Cochrane Library, and Web of Science were searched. Risk ratios (RRs) were adopted to estimate the relative BC incidence. A total of 7 prospective case-control publications were included, and 6 of them were distinct studies. Pooled analysis of data from the 6 studies involving 1824 women with incident BC and 3954 matched control participants with no overlapping of subjects among studies indicated no significant association between the highest levels of urinary aMT6s and the incidence of BC (RR = 0.97, 95% CI, 0.88–1.08, P = 0.56). Negative associations were observed in postmenopausal women (RR = 0.88, 95% CI, 0.75–1.02, P = 0.10), estrogen receptor positive BC (RR = 0.83, 95% CI, 0.64–1.07, P = 0.15), and studies using 12-hour overnight urine (RR = 0.81, 95% CI, 0.61–1.07, P = 0.13), all with borderline significances. Lag time or invasive degree did not interfere with the results. There was no evident publication bias detected by the Egger’s test and the funnel plot. Conclusively, the current evidence did not support a significant association between urinary aMT6s level and BC risk.

Urinary Melatonin in Relation to Postmenopausal Breast Cancer Risk According to Melatonin 1 Receptor Status.

Background: Urinary melatonin levels have been associated with a reduced risk of breast cancer in postmenopausal women, but this association might vary according to tumor melatonin 1 receptor (MT1R) expression.Methods: We conducted a nested case-control study among 1,354 postmenopausal women in the Nurses' Health Study, who were cancer free when they provided first-morning spot urine samples in 2000 to 2002; urine samples were assayed for 6-sulfatoxymelatonin (aMT6s, a major metabolite of melatonin). Five-hundred fifty-five of these women developed breast cancer before May 31, 2012, and were matched to 799 control subjects. In a subset of cases, immunohistochemistry was used to determine MT1R status of tumor tissue. We used multivariable-adjusted conditional logistic regression to estimate the relative risk (RR) of breast cancer [with 95% confidence intervals (CI)] across quartiles of creatinine-standardized urinary aMT6s level, including by MT1R subtype.Results: Higher urinary melatonin levels were suggestively associated with a lower overall risk of breast cancer (multivariable-adjusted RR = 0.78; 95% CI = 0.61-0.99, comparing quartile 4 vs. quartile 1; Ptrend = 0.08); this association was similar for invasive vs. in situ tumors (Pheterogeneity = 0.12). There was no evidence that associations differed according to MT1R status of the tumor (e.g., Pheterogeneity for overall breast cancer = 0.88).Conclusions: Higher urinary melatonin levels were associated with reduced breast cancer risk in this cohort of postmenopausal women, and the association was not modified by MT1R subtype.Impact: Urinary melatonin levels appear to predict the risk of breast cancer in postmenopausal women. However, future research should evaluate these associations with longer-term follow-up and among premenopausal women. Cancer Epidemiol Biomarkers Prev; 26(3); 413-9. ©2016 AACR.

The association of body size in early to mid-life with adult urinary 6-sulfatoxymelatonin levels among night shift health care workers.

BackgroundAdult body mass index (BMI) has been associated with urinary melatonin levels in humans; however, whether earlier-life body size is associated with melatonin, particularly among night shift workers, remains unknown.MethodsWe evaluated associations of birth weight, body shape (or somatotype) at ages 5 and 10, BMI at age 18 and adulthood, weight change since age 18, waist circumference, waist to hip ratio, and height with creatinine-adjusted morning urinary melatonin (6-sulfatoxymelatonin, aMT6s) levels among 1,343 healthy women (aged 32–53 at urine collection, 1996–1999) in the Nurses’ Health Study (NHS) II cohort. Using multivariable linear regression, we computed least-square mean aMT6s levels across categories of body size, and evaluated whether these associations were modified by night shift work.ResultsAdult BMI was inversely associated with aMT6s levels (mean aMT6s levels = 34 vs. 50 ng/mg creatinine, comparing adult BMI ≥30 vs. <20 kg/m2; Ptrend <0.0001); however, other measures of body size were not related to aMT6s levels after accounting for adult BMI. Night shifts worked prior to urine collection, whether recent or cumulatively over time, did not modify the association between adult BMI and aMT6s levels (e.g., Pinteraction = 0.72 for night shifts worked within two weeks of urine collection).ConclusionsOur results suggest that adult BMI, but not earlier measures of body size, is associated with urinary aMT6s levels in adulthood. These observations did not vary by night shift work status, and suggest that adult BMI may be an important mechanism by which melatonin levels are altered and subsequently influence chronic disease risk.

The effects of sleep and light at night on melatonin in adolescents.

The circadian hormone melatonin has wide-reaching effects on human physiology. In adolescents, the impact of nighttime light exposure and other modifiable behavioral factors on melatonin levels is poorly understood. We cross-sectionally examined the influence of nighttime behaviors on melatonin levels in 100 adolescents (average age: 15.7; 55 female, 45 male), who completed a self-administered questionnaire and provided a first morning urine sample to assay for urinary 6-sulfatoxymelatonin (aMT6s) levels. We used mixed-effects regression models to test for differences in aMT6s levels by categories of covariates. Self-reported sleep duration, ambient light levels during sleep, and use of electronics after turning off lights did not significantly predict aMT6s levels. Compared to those who reported weekend bedtimes before 11 pm, urinary aMT6s levels were significantly lower among participants reporting weekend bedtimes after midnight (52.5 vs. 38.0 ng/mg creatinine, P trend=0.007). Sleep interruption also appeared to be significantly associated with lower urinary aMT6s levels, but only if lights were turned on during sleep interruption (43.0 ng/mg creatinine for participants with sleep interruption but not turning lights on, vs. 24.6 ng/mg creatinine for participants reporting that they turned on the light when their sleep was interrupted P difference=0.032). Our study suggests that self-reported sleep-related behaviors have little to no effect on adolescent circadian systems, though larger studies are needed to confirm our findings.

Urinary Melatonin Levels, Sleep Disruption, and Risk of Prostate Cancer in Elderly Men

Melatonin has anticarcinogenic properties in experimental models. We undertook a case–cohort study of 928 Icelandic men without prostate cancer (PCa) nested within the Age, Gene/Environment Susceptibility (AGES)-Reykjavik cohort to investigate the prospective association between first morning-void urinary 6-sulfatoxymelatonin (aMT6s) levels and the subsequent risk for PCa, under the hypothesis that men with lower aMT6s levels have an increased risk for advanced PCa. We used weighted Cox proportional hazards models to assess the association between first morning-void aMT6s levels and PCa risk, adjusting for potential confounders. A total of 111 men were diagnosed with incident PCa, including 24 with advanced disease. Men who reported sleep problems at baseline had lower morning aMT6s levels compared with those who reported no sleep problems. Men with morning aMT6s levels below the median had a fourfold statistically significant increased risk for advanced disease compared with men with levels above the median (hazard ratio: 4.04; 95% confidence interval, 1.26–12.98). These results require replication in larger prospective studies with longer follow-up. Patient summaryIn this report, we evaluated the prospective association between urinary aMT6s levels and risk of PCa in an Icelandic population. We found that lower levels of aMT6s were associated with an increased risk for advanced PCa.

Psychomotor Performance of Truck Drivers Before and After Day Shifts

Objective: The aim of the present study is to evaluate the psychomotor performance of professional drivers in a field setting and in relation to certain variables, including age, behavioral factors, urinary levels of 6-sulfatoxymelatonin (aMT6s) normalized to urinary creatinine excretion, and the characteristics of the work shifts. Methods: The study was carried out on 16 professional male truck drivers aged 34–53 years. The drivers were submitted to the Vienna Reaction Test (RT) and Vienna Determination Test (DT) and provided urine specimens before and after 39 work shifts. They were also asked to record the road and traffic conditions (motorways, suburban and urban roads, traffic jams, visibility), duration, and mileage for each driving shift. Results: Using the 50th percentile as a cut point to arbitrarily categorize the performance measurements (Vienna RT reaction time and motor time, Vienna DT reaction time and number of correct reactions) into low and high performance levels, a direct relation emerged between the risk of low performance levels, as assessed by RT reaction time and motor time, and morning urinary levels of aMT6s categorized by tertiles. Before the driving shifts, the odds ratios of low performance levels (adjusted for start time and age) were 8.39 (95% confidence interval [CI]: 1.23–57.10) in the highest tertile compared to the lower tertile of aMT6s for RT reaction time and 4.15 (95% CI: 1.26–13.65) for RT motor time, respectively. After driving shifts, negative age-related effects on motor performance were detected. Multiple linear regression analyses, performed using early morning urinary aMT6s levels, age, and driving shift characteristics (start time, duration of driving shift) as predictors of performance measurements, showed aMT6s levels to be the primary independent predictor of RT reaction time before driving shifts and age as the primary predictor of RT motor time after driving shifts. No correlation was found between the risk of low performance levels as assessed by Vienna DT (reaction time and number of correct reactions) and aMT6s levels. Conclusions: The wide interindividual variability of urinary aMT6s excretion observed before driving shifts and the direct association between aMT6s levels in the early morning and performance measurements suggest that the circadian typology of drivers should be taken into account when scheduling the work shifts of professional drivers.

Pharmacokinetics of Melatonin in Preterm Infants

Background: There is strong experimental evidence of a neuroprotective effect of melatonin in immature animals. However, pharmacokinetic (PK) data on melatonin in preterm infants is lacking. The aim was to examine the preterm pharmacokinetic profile.Methods: We conducted a multi centre, open label study in infants < 31 weeks and < 7 days of age. A single intravenous melatonin infusion was given to successive groups. Melatonin and its primary urinary metabolite aMT6s were analysed by radioimmunoassay. Dosage was adjusted in subsequent groups until adult physiological levels were achieved (34.5-1185.3 pmol/L).Results: 18 preterms were enrolled. The results are summarized in table/graph below. Pre-infusion median plasma melatonin levels were 0pmol/L (range-0-165pmol/L). Blood melatonin levels closest to adult levels were achieved with a 2 hour infusion of 0.1mcg/kg/hr; the half life was 15.99 hours and Area under the curve-7234.74. Lower doses resulted in widely variable PK data. Figure [Plasma Melatonin Profile] Table Table Full size table Conclusion: Preterms have none or minimal circulating plasma melatonin. Urinary aMT6s levels are negligible in this gestational age group, probably because of immature liver metabolism. This melatonin PK data will be used in future clinical studies to test the hypothesis that melatonin has a neuroprotective effect.

Associations of urinary 6-sulfatoxymelatonin with biomarkers related to cardiovascular disease in Japanese women

Melatonin's potential preventive effect against cardiovascular disease (CVD) remains hypothetical. No study has evaluated the relationships between endogenous melatonin and the established blood biomarkers related to CVD. The objective of the present study is to examine the association between the endogenous melatonin level and various established blood biomarkers of risk of CVD, including white blood cell (WBC) count and plasma concentrations of lipids, homocysteine, uric acid (UA), and high-sensitivity C-reactive protein (hs-CRP). This cross-sectional study included 181 Japanese women who attended a health checkup program provided by a general hospital between March 2005 and March 2006. All study subjects responded to a self-administered questionnaire and were measured for weight, height, and blood pressure. Venous fasting blood and first-void morning urine were obtained from all subjects. Statistically significant inverse correlations were observed between urinary 6-sulfatoxymelatonin (aMT6s), the major metabolite of melatonin in urine, and WBC count, UA, and hs-CRP after controlling for age, body mass index, menopausal status, smoking status, diet, sleeping habits, and exercise ( r = −0.19, −0.21, and −0.24, respectively). There were no significant correlations between urinary aMT6s and plasma lipids and homocysteine. These data suggested that the urinary aMT6s level was inversely associated with established independent risk factors for CVD, such as WBC, UA, and hs-CRP. Endogenous melatonin may have implications for the risk of CVD.

Urinary 6-Sulphatoxymelatonin Levels and Risk of Breast Cancer in Premenopausal Women: The ORDET Cohort

Lower urinary melatonin levels are associated with a higher risk of breast cancer in postmenopausal women. Literature for premenopausal women is scant and inconsistent. In a prospective case-control study, we measured the concentration of 6-sulphatoxymelatonin (aMT6s) in the 12-hour overnight urine of 180 premenopausal women with incident breast cancer and 683 matched controls. In logistic regression models, the multivariate odds ratio (OR) of invasive breast cancer for women in the highest quartile of total overnight aMT6s output compared with the lowest was 1.43 [95% confidence interval (CI), 0.83-2.45; P(trend) = 0.03]. Among current nonsmokers, no association was existent (OR, 1.00; 95% CI, 0.52-1.94; P(trend) = 0.29). We observed an OR of 0.68 between overnight urinary aMT6s level and breast cancer risk in women with invasive breast cancer diagnosed >2 years after urine collection and a significant inverse association in women with a breast cancer diagnosis >8 years after urine collection (OR, 0.17; 95% CI, 0.04-0.71; P(trend) = 0.01). There were no important variations in ORs by tumor stage or hormone receptor status of breast tumors. Overall, we observed a positive association between aMT6s and risk of breast cancer. However, there was some evidence to suggest that this might be driven by the influence of subclinical disease on melatonin levels, with a possible inverse association among women diagnosed further from recruitment. Thus, the influence of lag time on the association between melatonin and breast cancer risk needs to be evaluated in further studies.

Urinary 6-Sulfatoxymelatonin and Mammographic Density in Japanese Women

A protective role of melatonin in the etiology of breast cancer has been suggested. The down-regulation of estrogen secretion by melatonin is thought to be a main cause of the link between melatonin and breast cancer risk. The present cross-sectional study examined whether the urinary 6-sulfatoxymelatonin (aMT6-s) level is inversely associated with mammographic density, which is regarded as a marker of breast cancer risk. The study subjects were 289 Japanese women (175 premenopausal and 123 postmenopausal women) who were recruited from participants in a mammographic breast cancer screening. The size of the total breast area and that of the dense area were measured quantitatively using an automated mammographic mass detection method. The concentration of aMT6-s was measured using first-void morning urine. In premenopausal women, the urinary aMT6-s level was significantly positively associated with percent density after controlling for covariates (P for trend=0.02). There was no significant association between urinary aMT6-s level and the percent density in postmenopausal women. We found no evidence that the melatonin level is inversely associated with mammographic density.

Association of Vegetable Intake with Urinary 6-Sulfatoxymelatonin Level

Melatonin is present in plants consumed as vegetables; however, only a limited number of vegetables have been tested for melatonin. The antiproliferative, antioxidative, and immunostimulatory effects of melatonin have been reported from laboratory studies. The potential protective effects of vegetable against cancer and cardiovascular disease may be partially attributable to an increased melatonin intake from vegetables. As a first step to test this hypothesis, we evaluated whether vegetable intake is associated with an increased urinary melatonin in 289 community-dwelling Japanese women. Diet, including vegetable consumption, was assessed with a validated 169-item semiquantitative food-frequency questionnaire. Urinary 6-sulfatoxymelatonin (aMT6-s) was measured in the first-void morning urines. There was a significant positive association between vegetable intake and urinary aMT6-s levels. The mean urinary aMT6-s was 16% higher in women with the highest quartile of vegetable intake than it was in those with the lowest quartile of intake. This association may be explained by the melatonin contained in vegetables. However, data should be regarded as preliminary because it is impossible to estimate dietary melatonin intake from vegetables and or from the entire diet because of incomplete data for melatonin in plants.

Circadian Phase in Adults of Contrasting Ages

There is evidence that aging may impair phase‐shifting responses to light synchronizers, which could lead to disturbed or malsynchronized circadian rhythms. To explore this hypothesis, 62 elder participants (age, 58 to 84 years) and 25 young adults (age, 19 to 40 years) were studied, first with baseline 1‐wk wrist actigraphy at home and then by 72 h in‐laboratory study using an ultra‐short sleep‐wake cycle. Subjects were awake for 60 minutes in 50 lux followed by 30 minutes of darkness for sleep. Saliva samples were collected for melatonin, and urine samples were collected for aMT6s (a urinary metabolite of melatonin) and free cortisol every 90 minutes. Oral temperatures were also measured every 90 minutes. The timing of the circadian rhythms was not significantly more variable among the elders. The times of lights‐out and wake‐up at home and urinary free cortisol occurred earlier among elders, but the acrophases (cosinor analysis‐derived peak time) of the circadian rhythm of salivary melatonin, urinary aMT6s, and oral temperature were not significantly phase‐advanced among elders. The estimated duration of melatonin secretion was 9.9 h among elders and 8.4 h among young adults (p<0.025), though the estimated half‐life of blood melatonin was shorter among elders (p<0.025), and young adults had higher saliva melatonin and urinary aMT6s levels. In summary, there was no evidence for circadian desynchronization associated with aging, but there was evidence of some rearrangement of the internal phase‐angles among the studied circadian rhythms.

Serum melatonin and urinary 6-sulfatoxymelatonin in major depression

In this study, serum melatonin and urinary 6-sulfatoxymelatonin (aMT6s) were measured in 14 major depressive inpatients, compared to 14 matched controls according to age, gender, season and hormonal treatment in women. Moreover, the relationship between serum melatonin and urinary aMT6s levels was analysed in the two groups. Results indicated that the two groups of subjects showed a clear melatonin rhythm without significant difference in the mean level of melatonin or aMT6s, in the area under the curve of melatonin or in the melatonin peak. However, the time of the nocturnal melatonin peak secretion was significantly delayed in depressive subjects as compared to healthy controls. Moreover, the depressed patients showed urinary aMT6s concentrations enhanced in the morning compared to night time levels, while these concentrations were lowered from the night to the morning in the control group. These results suggest that the melatonin production is phase-shifted in major depression.

Hormone levels of world class cyclists during the Tour of Spain stage race

Objectives—To evaluate the hormonal response to strenuous endurance exercise performed by elite athletes.Methods—Nine professional cyclists (mean (SD) age 28 (1) years; mean (SD) Vo2max 75.3 (2.3) ml/kg/min) who participated in...

Prediction of nocturnal plasma melatonin from morning urinary measures.

A growing literature indicates that blood levels of the hormone melatonin may have important implications for human health and well-being. Melatonin is synthesized and released into the general circulation at night, however, and it is seldom feasible to draw blood samples at night in epidemiological studies. There is some evidence that levels of urinary melatonin and of 6-sulfatoxymelatonin (aMT6s), the major metabolite of melatonin, accurately reflect nocturnal plasma melatonin. If this is the case, urinary assays could be powerful tools for epidemiological studies. A laboratory-based study was performed to examine the relationships between nocturnal plasma melatonin, morning urinary melatonin, and morning urinary aMT6s levels in 78 men. The relationship between total nocturnal plasma melatonin and both urinary aMT6s corrected for creatinine and urinary melatonin is significant. Combining the two urinary measures accounts for 72% of the variance in total plasma melatonin. Peak nocturnal plasma melatonin also was significantly related to urinary melatonin and to aMT6s. The urinary measures show good sensitivity and specificity in identifying individual differences in nocturnal plasma melatonin levels. These results support the inclusion of morning urine samples to assess the contribution of the hormone melatonin in occupational or residential studies involving healthy, young men.