Acute impact of light at night and exogenous melatonin on subjective appetite and plasma leptin.

This study investigates the possible effect of exogenous melatonin on appetite control by investigating plasma leptin and subjective appetite parameters. Nine healthy male participants [26 ± 1.3 years, body mass index (BMI) 24.8 ± 0.8 kg/m2] (mean ± SD) were recruited. The study was designed as a randomized three-way cross-over design; light (>500 lux) (LS), dark (<5 lux) + exogenous melatonin (DSC), and light (>500 lux) + exogenous melatonin (LSC), with an interval of at least 7 days between each session. Each session started at 18:00 h and ended at 06:00 h the following day. Participants were awake and in a semi-recumbent position during each clinical session. The meal times were individualized according to melatonin onset from 48 h sequential urine collection, whereas melatonin intake was given 90 min before the evening meal. Subjective appetite parameters were collected at 30 min intervals during each session. Plasma leptin was collected at specific time points to analyze pre-prandial and postprandial leptin. Subjective hunger and desire to eat were reported higher in LS than DSC and LSC (P = 0.03, and P = 0.001). Plasma leptin showed a significant increase in LSC and DSC (p = 0.007). This study suggested a positive impact of exogenous melatonin on subjective appetite and plasma leptin.

The effect of melatonin on glucose tolerance, insulin sensitivity and lipid profiles after a late evening meal in healthy young males.

The suppression of melatonin by light at night (LAN) has been associated with a disruption of SCN function and biological processes. This study aimed to explore the impact of melatonin on glucose and lipid metabolism before and after a late evening meal. Nine healthy male participants (26 ± 1.3 years, BMI 24.8 ± 0.8 kg/m2 (mean ± SD) were randomly categorised into a three-way cross-over design protocol: light (>500 lux) (LS), dark (<5 lux) + exogenous melatonin (DSC) and light (>500 lux) + exogenous melatonin (LSC). All participants were awake in a semi-recumbent position during each clinical session, which started at 18 00 h and ended at 06:00 h the following day. The meal times were individualised according to melatonin onset estimated from the participants' 48-h sequential urine collection. The administration of exogenous melatonin was conducted 90 min before the evening meal. Saliva and plasma samples were collected at specific time points to analyse the glucose, insulin, NEFAs, TAGs, cortisol and melatonin levels. Participants demonstrated a significant reduction in postprandial plasma glucose, insulin and TAGs levels in the presence of melatonin (LSC and DSC) compared to LS (p = .002, p = .02 and p = .007, respectively). Pre-prandial plasma NEFAs were significantly lower in LS than DSC and LSC as melatonin rose (p < .001). Exogenous melatonin administrated before an evening test meal improved glucose tolerance, insulin sensitivity and reduced postprandial TAGs. This study could have implications for shift workers who may have lower melatonin levels at night due to light suppression.

A single night light exposure acutely alters hormonal and metabolic responses in healthy participants.

Many animal studies have reported an association between melatonin suppression and the disturbance of metabolic responses; yet, few human studies have investigated bright light effects on metabolic and hormonal responses at night. This study investigated the impact of light on plasma hormones and metabolites prior to, and after, an evening meal in healthy participants. Seventeen healthy participants, 8 females (22.2 ± 2.59 years, mean ± s.d.) and 9 males (22.8 ± 3.5 years) were randomised to a two-way cross-over design protocol; dim light (DL) (<5 lux) and bright light (BL) (>500 lux) sessions, separated by at least seven days. Saliva and plasma samples were collected prior to and after a standard evening meal at specific intervals. Plasma non-esterified fatty acid (NEFA) levels were significantly higher pre-meal in DL compared to BL (P < 0.01). Plasma glucose and insulin levels were significantly greater post-meal in the BL compared to DL session (P = 0.02, P = 0.001), respectively. Salivary melatonin levels were significantly higher in the DL compared to those in BL session (P = 0.005). BL at night was associated with significant increases in plasma glucose and insulin suggestive of glucose intolerance and insulin insensitivity. Raised pre-prandial NEFA levels may be due to changes in insulin sensitivity or the presence of melatonin and/or light at night. Plasma triglyceride (TAG) levels were the same in both sessions. These results may explain some of the health issues reported in shift workers; however, further studies are needed to elucidate the cause of these metabolic changes.

Mood, alertness, and performance in response to sleep deprivation and recovery sleep in experienced shiftworkers versus non-shiftworkers.

Previous studies have shown increased sleepiness and mood changes in shiftworkers, which may be due to sleep deprivation or circadian disruption. Few studies, however, have compared responses of experienced shiftworkers and non-shiftworkers to sleep deprivation in an identical laboratory setting. The aim of this laboratory study, therefore, was to compare long-term shiftworkers and non-shiftworkers and to investigate the effects of one night of total sleep deprivation (30.5 h of continuous wakefulness) and recovery sleep on psychomotor vigilance, self-rated alertness, and mood. Eleven experienced male shiftworkers (shiftwork ≥5 yrs) were matched with 14 non-shiftworkers for age (mean ± SD: 35.7 ± 7.2 and 32.5 ± 6.2 yrs, respectively) and body mass index (BMI) (28.7 ± 3.8 and 26.6 ± 3.4 kg/m(2), respectively). After keeping a 7-d self-selected sleep/wake cycle (7.5/8 h nocturnal sleep), both groups entered a laboratory session consisting of a night of adaptation sleep and a baseline sleep (each 7.5/8 h), a sleep deprivation night, and recovery sleep (4-h nap plus 7.5/8 h nighttime sleep). Subjective alertness and mood were assessed with the Karolinska Sleepiness Scale (KSS) and 9-digit rating scales, and vigilance was measured by the visual psychomotor vigilance test (PVT). A mixed-model regression analysis was carried out on data collected every hour during the sleep deprivation night and on all days (except for the adaptation day), at .25, 4.25, 5.25, 11.5, 12.5, and 13.5 h after habitual wake-up time. Despite similar circadian phase (melatonin onset), demographics, food intake, body posture, and environmental light, shiftworkers felt significantly more alert, more cheerful, more elated, and calmer than non-shiftworkers throughout the laboratory study. In addition, shiftworkers showed a faster median reaction time (RT) compared to non-shiftworkers, although four other PVT parameters did not differ between the groups. As expected, both groups showed a decrease in subjective alertness and PVT performance during and following the sleep deprivation night. Subjective sleepiness and most aspects of PVT performance returned to baseline levels after a nap and recovery sleep. The mechanisms underlying the observed differences between shiftworkers and non-shiftworkers require further study, but may be related to the absence of shiftwork the week prior to and during the laboratory study as well as selection into and out of shiftwork.

Heart rate variability and endothelial function after sleep deprivation and recovery sleep among male shift and non-shift workers.

OBJECTIVES: Endothelial dysfunction and alterations in heart rate variability (HRV) as well as sleep deprivation and shift work have been associated with cardiovascular disease. The aim of this study was to compare HRV and endothelial function among shift and matched non-shift workers in response to total sleep deprivation and recovery sleep under identical laboratory settings. METHODS: Eleven experienced male shift workers (shift work ≥ 5 years) and 14 non-shift workers were matched for age, body mass index, and cholesterol. HRV parameters [eg, HR variance and low frequency/high frequency (LF/HF) ratio] were derived from 5-minute electrocardiogram bins at 0.25, 4.25, 11.5, 12.5, and 13.5 hours after habitual wake-up time and endothelial function was assessed by flow-mediated dilatation (FMD) using ultrasound at 0.75 and 10.75 hours after habitual wake-up time, following baseline sleep, total sleep deprivation, and recovery sleep (posture- and food-controlled throughout). Circadian phase was assessed before baseline sleep by salivary dim light melatonin onset. RESULTS: There was no difference in circadian phase between shift and non-shift workers. HR variance was highest at 0.25 hours following total sleep deprivation and lowest after recovery sleep. A significantly higher LF/HF ratio, significantly lower HR variance, and a trend for a lower %FMD (P=0.08) were observed among shift compared to non-shift workers. CONCLUSION: Despite similar demographics, circadian phase, posture and food intake, differences in endothelial function and HRV were observed in the two groups, which may reflect higher sympathetic and/or lower parasympathetic activity, contributing to increased cardiovascular risk among the shift workers.

Effect of meal timing and glycaemic index on glucose control and insulin secretion in healthy volunteers.

Shiftworkers have a higher risk of CHD and type 2 diabetes. They consume a large proportion of their daily energy and carbohydrate intake in the late evening or night-time, a factor which could be linked to their increase in disease risk. We compared the metabolic effects of varying both dietary glycaemic index (GI) and the time at which most daily energy intake was consumed. We hypothesised that glucose control would be optimal with a low-GI diet, consumed predominantly early in the day. A total of six healthy lean volunteers consumed isoenergetic meals on four occasions, comprising either high- or low-GI foods, with 60 % energy consumed predominantly early (breakfast) or late (supper). Interstitial glucose was measured continuously for 20 h. Insulin, TAG and non-esterified fatty acids were measured for 2 h following every meal. Highest glucose values were observed when large 5021 kJ (1200 kcal) high-GI suppers were consumed. Glucose levels were also significantly higher in predominantly late high- v. low-GI meals (P<0·01). Using an estimate of postprandial insulin sensitivity throughout the day, we demonstrate that this follows the same trend, with insulin sensitivity being significantly worse in high energy consumed in the evening meal pattern. Both meal timing and GI affected glucose tolerance and insulin secretion. Avoidance of large, high-GI meals in the evening may be particularly beneficial in improving postprandial glucose profiles and may play a role in reducing the risk of type 2 diabetes; however, longer-term studies are needed to confirm this.

Effect of total sleep deprivation on postprandial metabolic and insulin responses in shift workers and non-shift workers.

Epidemiological studies have shown that shift workers are at a greater risk of developing cardiovascular disease which may, in part, be related to metabolic and hormonal changes. Partial sleep deprivation, a common consequence of rotating shift work, has been shown to affect glucose tolerance and insulin sensitivity. The current study investigated the effects of one night of total sleep deprivation, as a proxy for the first night shift, on postprandial glucose, insulin and lipid (triacylglycerols (TAGs) and non-esterified fatty acids (NEFAs)) responses under controlled laboratory conditions in shift workers and non-shift workers. Eleven experienced shift workers (35.7+/-7.2 years, mean+/-s.d.) who had worked in shifts for 8.7+/-5.25 years were matched with 13 non-shift workers who had worked for 32.8+/-6.4 years. After an adaptation night and a baseline sleep night, volunteers were kept awake for 30.5 h, followed by a nap (4 h) and recovery sleep. Blood samples were taken prior to and after a standard breakfast following baseline sleep, total sleep deprivation and recovery sleep. Basal TAG levels prior to the standard breakfast were significantly lower after sleep deprivation, indicating higher energy expenditure. Basal NEFA levels were significantly lower after recovery sleep. Postprandial insulin and TAG responses were significantly increased, and the NEFA response was decreased after recovery sleep, suggestive of insulin insensitivity. Although there were no overall significant differences between non-shift workers and shift workers, non-shift workers showed significantly higher basal insulin levels, lower basal NEFA levels, and an increased postprandial insulin and a decreased NEFA response after recovery sleep. In future, the reasons for these inter-group differences are to be investigated.

Circadian variation in endothelial function is attenuated in postmenopausal women.

OBJECTIVE: The present study was undertaken to investigate the possible existence of an endogenously generated circadian rhythm in endothelial function in women and whether this rhythm is altered after the menopause. METHODS: Healthy non smoking women (11 pre-menopausal and 13 postmenopausal women) were studied during a 22 h period under constant routine conditions; endothelium-dependent (flow-mediated dilation (%FMD)) and -independent (glyceryl-trintrate (GTN)-mediated) function was assessed every 2 and 4 h, respectively, by high-resolution ultrasound of the brachial artery. RESULTS: %FMD and %GTN was significantly higher in pre-menopausal women (9.9+/-1.0%FMD (mean+/-S.E.M.); 18.2+/-1.8%GTN; P<0.01) compared with postmenopausal women (6.5+/-0.5%FMD; 11.5+/-1.6%GTN). A significant day-night variation in %FMD was observed pre-menopausal women (day 9.2+/-0.8%; night 10.4+/-1%; P<0.05) with an attenuated rhythm in postmenopausal women (day 6.8+/-0.6%; night 6.0+/-0.4%). CONCLUSIONS: The findings show a circadian rhythm in %FMD in pre-menopausal women, which disappears after the menopause. The reduction in %FMD and an absence of a day-night variation in %FMD in postmenopausal women may have important implications for the incidence of coronary heart disease in women after the menopause.

The effects of exclusion of dietary egg and milk in the management of asthmatic children: a pilot study.

Current understanding of the use of exclusion diets in the management of asthma in children is limited and controversial. The aim of this study was to examine the effects of excluding eggs and milk on the occurrence of symptoms in children with asthma and involved 22 children aged between three and 14 years clinically diagnosed as having mild to moderate disease. The investigation was single blind and prospective, and parents were given the option of volunteering to join the 'experiment' group, avoiding eggs, milk and their products for eight weeks, or the 'control' group, who consumed their customary food. Thirteen children were recruited to the experimental group and nine to the control group. A trained paediatrician at the beginning and end of the study period assessed the children. A seven-day assessment of food intake was made before, during and immediately after the period of dietary intervention in both groups. A blood sample was taken from each child for determination of food specific antibodies and in those children who could do so, the peak expiratory flow rate (PEFR) was measured. Based on the recommended nutrient intake (RNI), the mean percentage energy intake of the children in the experimental group was significantly lower (p < 0.05) in the experimental group. After the eight-week study period and compared with baseline values, the mean serum anti-ovalbumin IgG and anti-beta lactoglobulin IgG concentrations were statistically significantly reduced (p < 0.05) for both in the experimental group. In contrast, the values for anti-ovalbumin IgG in the control group were significantly increased and those for anti-beta lactoglobulin IgG were practically unchanged. The total IgE values were unchanged in both groups. Over the study period, the PEFR in those children in the experimental group able to perform the test was significantly increased, but no such change was noted in the children in the control group who could do the test. These results suggest that even over the short time period of eight weeks, an egg- and milk-free diet can reduce atopic symptoms and improve lung function in asthmatic children.

Biological rhythms, endothelial health and cardiovascular disease.

The activity of several components of the vascular system appears to be diurnally regulated. Endothelial cell activation, leukocyte and platelet interactions and lipoprotein metabolism have all been shown to vary with time of day, but whether these variations are due to the endogenous circadian clock, exogenous factors, such as the light-dark cycle, or an interaction between the two remains to be determined. Endothelium-dependent vasodilation also varies diurnally. This rhythmicity is lost in individuals with established coronary disease has been shown to occur in the early stages of atherosclerosis. The incidence of coronary events appears to be higher in the early hours of the morning, this may be related to heightened activity of the autonomic nervous system at this time. Higher circulating levels of catecholamines in the morning are associated with increased vascular tone, affecting circulating blood volume and blood pressure. Time dependent variations may be of particular significance for individuals with disrupted circadian rhythms, including rotating shift workers, transmeridian travellers and blind individuals with no light perception. Variations in endothelial function are observed during the menstrual cycle, varying with circulating oestrogen levels. Oestrogen deficiency in postmenopausal women may contribute to endothelial dysfunction, together with other modifiable risk factors. The absolute risk of coronary disease is greater for men than for pre-menopausal women. Following the menopause gender differences in coronary risk are thought to diminish, although this remains controversial. This review focuses on the influence of both endogenous biological rhythms and environmental factors on the function and health of the human vascular system.