Light therapy improves diurnal blood pressure control in night shift workers via reduction of catecholamines: the EuRhythDia study.

OBJECTIVES: Night shift work is associated with high rates of hypertension and cardiometabolic disease, which are linked to disrupted circadian rhythms. We hypothesized that timed light therapy might improve disrupted circadian rhythms and stabilize diurnal control of blood pressure and glucose in night shift workers. METHODS: We randomized 24 rotating night shift workers (mean age, 36 ±â€Š13 years, 7 men) who had spent a median of 6 years on rotating night shifts (median, six night shifts per month) to 12 weeks of light therapy or no intervention and compared them with 12 daytime workers (37 ±â€Š11 years, 6 men). We measured oral glucose tolerance (OGTT), 24-h blood pressure and arterial stiffness, and the circadian profiles of melatonin, cortisol, metanephrine and nor-metanephrine at baseline, after 12 weeks of intervention, and 12 weeks after the end of intervention. RESULTS: At baseline, fewer night shift workers showed dipper status as compared with daytime workers (29 vs. 58%; P < 0.001). After 12 weeks of light therapy, there was a highly significant increase in the proportion of dippers (to 58%; P < 0.0001). We also observed a significant decrease in serum glucose during OGTT in the light therapy group (-22%; P < 0.05) with no change in serum insulin. Whilst circadian profiles of melatonin and cortisol were unchanged, plasma metanephrine and nor-metanephrine levels were significantly reduced in the light therapy group (P < 0.01). CONCLUSION: Timed light therapy improves diurnal blood pressure control and glucose tolerance in rotating night shift workers. This effect is unrelated to melatonin and cortisol but is paralleled by reduced catecholamine levels.

Differential Effects of DHA- and EPA-Rich Oils on Sleep in Healthy Young Adults: A Randomized Controlled Trial.

Emerging evidence suggests that adequate intake of omega-3 polyunsaturated fatty acids (n-3 PUFAs), which include docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), might be associated with better sleep quality. N-3 PUFAs, which must be acquired from dietary sources, are typically consumed at suboptimal levels in Western diets. Therefore, the current placebo-controlled, double-blind, randomized trial, investigated the effects of an oil rich in either DHA or EPA on sleep quality in healthy adults who habitually consumed low amounts of oily fish. Eighty-four participants aged 25-49 years completed the 26-week intervention trial. Compared to placebo, improvements in actigraphy sleep efficiency (p = 0.030) and latency (p = 0.026) were observed following the DHA-rich oil. However, these participants also reported feeling less energetic compared to the placebo (p = 0.041), and less rested (p = 0.017), and there was a trend towards feeling less ready to perform (p = 0.075) than those given EPA-rich oil. A trend towards improved sleep efficiency was identified in the EPA-rich group compared to placebo (p = 0.087), along with a significant decrease in both total time in bed (p = 0.032) and total sleep time (p = 0.019) compared to the DHA-rich oil. No significant effects of either treatment were identified for urinary excretion of the major melatonin metabolite 6-sulfatoxymelatonin. This study was the first to demonstrate some positive effects of dietary supplementation with n-3 PUFAs in healthy adult normal sleepers, and provides novel evidence showing the differential effects of n-3 PUFA supplements rich in either DHA or EPA. Further investigation into the mechanisms underpinning these observations including the effects of n-3 PUFAs on sleep architecture are required.

Resetting the late timing of 'night owls' has a positive impact on mental health and performance.

BACKGROUND: There is conflict between living according to our endogenous biological rhythms and our external environment, with disruptions resulting in negative consequences to health and performance. This is often documented in shift work and jet lag, but 'societal norms' (eg, typical working hours) can create profound issues for 'night owls', people whose internal biological timing predisposes them to follow an unusually late sleep-wake cycle. Night owls have also been associated with health issues, mood disturbances, poorer performance and increased mortality rates. METHODS: This study used a randomized control trial design aimed to shift the late timing of night owls to an earlier time (phase advance), using non-pharmacological, practical interventions in a real-world setting. These interventions targeted light exposure (through earlier wake up/sleep times), fixed meals times, caffeine intake and exercise. RESULTS: Overall, participants demonstrated a significant advance of ∼2 h in sleep/wake timings as measured by actigraphy and circadian phase markers (dim light melatonin onset and peak time of the cortisol awakening response), whilst having no adverse effect on sleep duration. Notably, the phase advance was accompanied by significant improvements to self-reported depression and stress, as well as improved cognitive (reaction time) and physical (grip strength) performance measures during the typical 'suboptimal' morning hours. CONCLUSIONS: Our findings propose a novel strategy for shifting clock timing towards a pattern that is more aligned to societal demands that could significantly improve elements of performance, mental health and sleep timing in the real world.

Blue-Enriched Lighting for Older People Living in Care Homes: Effect on Activity, Actigraphic Sleep, Mood and Alertness.

OBJECTIVE: Environmental (little outdoor light; low indoor lighting) and age-related physiological factors (reduced light transmission through the ocular lens, reduced mobility) contribute to a light-deprived environment for older people living in care homes. METHODS: This study investigates the effect of increasing indoor light levels with blue-enriched white lighting on objective (rest-activity rhythms, performance) and self-reported (mood, sleep, alertness) measures in older people. Eighty residents (69 female), aged 86 ± 8 yrs (mean ± SD), participated (MMSE 19 ± 6). Overhead fluorescent lighting was installed in communal rooms (n=20) of seven care homes. Four weeks of blue-enriched white lighting (17000 K ≅ 900 lux) were compared with four weeks of control white lighting (4000 K ≅ 200 lux), separated by three weeks wash-out. Participants completed validated mood and sleep questionnaires, psychomotor vigilance task (PVT) and wore activity and light monitors (AWL). Rest-activity rhythms were assessed by cosinor, non-parametric circadian rhythm (NPCRA) and actigraphic sleep analysis. Blue-enriched (17000 K) light increased wake time and activity during sleep decreasing actual sleep time, sleep percentage and sleep efficiency (p < 0.05) (actigraphic sleep). Compared to 4000 K lighting, blue-enriched 17000 K lighting significantly (p < 0.05) advanced the timing of participants' rest-activity rhythm (cosinor), increased daytime and night-time activity (NPCRA), reduced subjective anxiety (HADA) and sleep quality (PSQI). There was no difference between the two light conditions in daytime alertness and performance (PVT). CONCLUSION: Blue-enriched lighting produced some positive (increased daytime activity, reduced anxiety) and negative (increased night-time activity, reduced sleep efficiency and quality) effects in older people.

Effect of tart cherry juice (Prunus cerasus) on melatonin levels and enhanced sleep quality.

BACKGROUND: Tart Montmorency cherries have been reported to contain high levels of phytochemicals including melatonin, a molecule critical in regulating the sleep-wake cycle in humans. PURPOSE: The aim of our investigation was to ascertain whether ingestion of a tart cherry juice concentrate would increase the urinary melatonin levels in healthy adults and improve sleep quality. METHODS: In a randomised, double-blind, placebo-controlled, crossover design, 20 volunteers consumed either a placebo or tart cherry juice concentrate for 7 days. Measures of sleep quality recorded by actigraphy and subjective sleep questionnaires were completed. Sequential urine samples over 48 h were collected and urinary 6-sulfatoxymelatonin (major metabolite of melatonin) determined; cosinor analysis was used to determine melatonin circadian rhythm (mesor, acrophase and amplitude). In addition, total urinary melatonin content was determined over the sampled period. Trial differences were determined using a repeated measures ANOVA. RESULTS: Total melatonin content was significantly elevated (P < 0.05) in the cherry juice group, whilst no differences were shown between baseline and placebo trials. There were significant increases in time in bed, total sleep time and sleep efficiency total (P < 0.05) with cherry juice supplementation. Although there was no difference in timing of the melatonin circardian rhythm, there was a trend to a higher mesor and amplitude. CONCLUSIONS: These data suggest that consumption of a tart cherry juice concentrate provides an increase in exogenous melatonin that is beneficial in improving sleep duration and quality in healthy men and women and might be of benefit in managing disturbed sleep.

Age-related changes in acute and phase-advancing responses to monochromatic light.

Reduced sensitivity to short-wavelength (blue) light with age has been shown for light-induced melatonin suppression. The current research aimed to determine if a similar age-related reduction occurs in subjective alertness, mood, and circadian phase-advancing responses. Young (n = 11, 23.0 +/- 2.9 years) and older (n = 15, 65.8 +/- 5.0 years) healthy males participated in laboratory sessions that included a 2-h intermittent monochromatic light exposure, individually timed to begin 8.5 h after their dim light melatonin onset (DLMO) determined in a prior visit. In separate sessions, pupil-dilated subjects were exposed to short-wavelength blue (lambda max 456 nm) and medium-wavelength green (lambda max 548 nm) light matched for photon density (6 x 1013 photons/cm2/sec). Subjective alertness, sleepiness, and mood were verbally assessed every 15 to 30 min before, during, and up to 5 h after the light exposure. The magnitude of phase advance was assessed as the difference in plasma melatonin rhythm phase markers before and after light exposure. Following blue light exposure, responses in older men were significantly diminished compared with young men for subjective alertness (p < 0.0001), sleepiness (p < 0.0001), and mood (p < 0.05) during and after light exposure. There was no significant effect of age on these parameters following green light exposure. The phase advances to both blue and green light were larger in the young than older subjects, but did not reach statistical significance. In general, phase advances to blue light were slightly larger than to green light in both young and old, but did not reach statistical significance. The current results add to previous findings demonstrating reduced responsiveness to the acute effects of blue light in older people (melatonin suppression, alertness). However, under the study paradigm, the phase-advancing response to light does not appear to be significantly impaired with age.

Nonvisual responses to light exposure in the human brain during the circadian night.

The brain processes light information to visually represent the environment but also to detect changes in ambient light level. The latter information induces non-image-forming responses and exerts powerful effects on physiology such as synchronization of the circadian clock and suppression of melatonin. In rodents, irradiance information is transduced from a discrete subset of photosensitive retinal ganglion cells via the retinohypothalamic tract to various hypothalamic and brainstem regulatory structures including the hypothalamic suprachiasmatic nuclei, the master circadian pacemaker. In humans, light also acutely modulates alertness, but the cerebral correlates of this effect are unknown. We assessed regional cerebral blood flow in 13 subjects attending to auditory and visual stimuli in near darkness following light exposures (>8000 lux) of different durations (0.5, 17, 16.5, and 0 min) during the biological night. The bright broadband polychromatic light suppressed melatonin and enhanced alertness. Functional imaging revealed that a large-scale occipito-parietal attention network, including the right intraparietal sulcus, was more active in proportion to the duration of light exposures preceding the scans. Activity in the hypothalamus decreased in proportion to previous illumination. These findings have important implications for understanding the effects of light on human behavior.