Timely use of in-car dim blue light and blue blockers in the morning does not improve circadian adaptation of fast rotating shift workers.

Circadian adaptation to night work usually does not occur in naturalistic conditions, largely due to exposure to low levels of light during the night and light in the morning on the way home. This leads to circadian misalignment, which has documented deleterious effects on sleep and functioning during waking hours. Chronic circadian misalignment is also being increasingly associated with long-term health comorbidities. As the circadian system is mostly sensitive to short wavelengths (i.e., blue light) and less sensitive to long wavelengths (i.e., red light), shaping light exposure in a "wavelength-wise" manner has been proposed to promote partial adaptation to night shifts, and, therefore, alleviate circadian rhythms disruption. This report presents results from two cross-over designed studies that aimed to investigate the effects of three different light conditions on circadian phase, sleepiness, and alertness of police patrol officers on a rotating shift schedule. The first study took place during summer (n = 15) and the second study (n = 25) during winter/early spring. In both studies, all participants went through three conditions composed of four consecutive night shifts: 1) in-car dim blue light exposure during the night shift and wearing of blue-blocking glasses (BBG) in the morning after 05:00 h; 2) in-car red light exposure during the night shift and wearing of BBG in the morning after 05:00 h; 3) a control condition with no intervention. To assess circadian phase position, salivary melatonin was collected hourly the night before and the night after each condition. Sleep was monitored by wrist actigraphy. Also, a 10-min Psychomotor Vigilance-Task was administered at the beginning and end of each night shift and the Karolinska Sleepiness Scale was completed every 2 h during each night shift. In the summer study, no difference was found in alertness and sleepiness between conditions. Participants though exhibited greater (≈3 h) phase delay after four consecutive night shifts in the control condition (in which morning light exposure was expected to prevent phase delay) than after the blue and red conditions (≈2 h) (in which wearing BBG were expected to promote phase delay). In the second study performed during the winter/early spring, a comparable ≈2 h phase delay was found in each of the three conditions, with no difference in alertness and sleepiness between conditions. In conclusion, participants in both studies exhibited modest phase delay across the four night shifts, even during the control conditions. Still, re-entrainment was not fast enough to produce partial circadian adaptation after four night shifts. A greater number of consecutive night shifts may be necessary to produce enough circadian alignment to elicit benefits on sleepiness and alertness in workers driving a motorized vehicle during night shifts. In-car dim blue light exposure combined with the wearing of BBG in the morning did not show the expected benefits on circadian adaptation, sleepiness, and alertness in our studies. Higher levels of light may be warranted when implementing light intervention in a motorized vehicle setting.

[When a season means depression]. / Quand la saison devient synonyme de dépression.

Although becoming more and more recognized among physicians and psychiatrists the etiology of seasonal affective disorder (SAD) remains unclear. Indeed, the only incontestable fact is the close link between the decrease in sunlight occurring during fall and winter and the onset of depressive symptoms. But why does this seasonal decrease in the amount of light trigger a depression in some individuals while not affecting others? Why and how has sun exposure such an impact on brain-mood regulation? This review intends to shed some light on the main neurochemical hypotheses that have been advanced for the past 25 years. While several hypotheses have been advanced to explain SAD, the present review will focus on three major suspects which are: (1) melatonin due to its crucial role in circadian rhythms (2) serotonin which has been linked with depressive disorders in general and atypical symptoms and (3) catecholamine because as for serotonin, many data reported an implication of these neurotransmitter family in depressive disorders. However, similarly to other reviews about SAD, we conclude that none of those could explain the pathophysiology of this northern disease on its own.

Investigating the contribution of short wavelengths in the alerting effect of bright light.

INTRODUCTION: Short-wavelengths can have an acute impact on alertness, which is allegedly due to their action on intrinsically photosensitive retinal ganglion cells. Classical photoreceptors cannot, however, be excluded at this point in time as contributors to the alerting effect of light. The objective of this study was to compare the alerting effect at night of a white LED light source while wearing blue-blockers or not, in order to establish the contribution of short-wavelengths. MATERIALS AND METHODS: 20 participants stayed awake under dim light (< 5 lx) from 23:00 h to 04:00 h on two consecutive nights. On the second night, participants were randomly assigned to one light condition for 30 min starting at 3:00 h. Group A (5M/5F) was exposed to 500 µW/cm(2) of unfiltered LED light, while group B (4M/6F) was required to wear blue-blocking glasses, while exposed to 1500 µW/cm(2) from the same light device in order to achieve 500 µW/cm(2) at eye level (as measured behind the glasses). Subjective alertness, energy, mood and anxiety were assessed for both nights at 23:30 h, 01:30 h and 03:30 h using a visual analog scale (VAS). Subjective sleepiness was assessed with the Stanford Sleepiness Scale (SSS). Subjects also performed the Conners' Continuous Performance Test II (CPT-II) in order to assess objective alertness. Mixed model analysis was used to compare VAS, SSS and CPT-II parameters. RESULTS: No difference between group A and group B was observed for subjective alertness, energy, mood, anxiety and sleepiness, as well as CPT-II parameters. Subjective alertness (p < 0.001), energy (p < 0.001) and sleepiness (p < 0.05) were, however improved after light exposure on the second night independently of the light condition. CONCLUSIONS: The current study shows that when sleepiness is high, the alerting effect of light can still be triggered at night in the absence of short-wavelengths with a 30 minute light pulse of 500 µW/cm(2). This suggests that the underlying mechanism by which a brief polychromatic light exposure improves alertness is not solely due to short-wavelengths through intrinsically photosensitive retinal ganglion cells.

Day and night shift schedules are associated with lower sleep quality in Evening-types.

Eveningness has been suggested as a facilitating factor in adaptation to shift work, with several studies reporting evening chronotypes (E-types) as better sleepers when on night shifts. Conversely, eveningness has been associated with more sleep complaints during day shifts. However, sleep during day shifts has received limited attention in previous studies assessing chronotypes in shift workers. Environmental light exposure has also been reported to differ between chronotypes in day workers. Activity is also known to provide temporal input to the circadian clock. Therefore, the aim of this study was to compare objective sleep, light exposure and activity levels between chronotypes, both during the night and day shifts. Thirty-nine patrol police patrol officers working on a fast rotating shift schedule (mean age ± SD: 28.9 ± 3.2 yrs; 28 males) participated in this study. All subjects completed the Morningness-Eveningness Questionnaire (MEQ). Sleep and activity were monitored with actigraphy (Actiwatch-L; Mini-Mitter/Respironics, Bend, OR) for four consecutive night shifts and four consecutive day shifts (night work schedule: 00:00 h-07:00 h; day work schedule: 07:00 h-15:00 h). Sleep and activity parameters were calculated with Actiware software. MEQ scores ranged from 26 to 56; no subject was categorized as Morning-type. E-types (n = 13) showed significantly lower sleep efficiency, longer snooze time and spent more time awake after sleep onset than Intermediate-types (I-types, n = 26) for both the night and day shifts. E-types also exhibited shorter and more numerous sleep bouts. Furthermore, when napping was taken into account, E-types had shorter total sleep duration than I-types during the day shifts. E-types were more active during the first hours of their night shift when compared to I-types. Also, all participants spent more time active and had higher amount of activity per minute during day shifts when compared to night shifts. No difference was found regarding light exposure between chronotypes. In conclusion, sleep parameters revealed poorer sleep quality in E-types for both the night and day shifts. These differences could not be explained by sleep opportunity, light exposure or activity levels. This study challenges the notion that E-types adapt better to night shifts. Further studies must verify whether E-types exhibit lower sleep quality than Morning-types.

Using blue-green light at night and blue-blockers during the day to improves adaptation to night work: a pilot study.

BACKGROUND: Bright light at night paired with darkness during the day seem to facilitate adaptation to night work. Considering the biological clock sensitive to short wavelengths, we investigated the possibility of adaptation in shift workers exposed to blue-green light at night, combined with using blue-blockers during the day. METHODS: Four sawmill shift workers were evaluated during two weeks of night shifts (control and experimental) and one week of day shifts. Throughout the experimental week, ambient light (approximately 130 lx) was supplemented with blue-green light (200 lx) from 00:00 h to: 05:00 h on Monday and Tuesday, 06:00 h on Wednesday and 07:00 h on Thursday. Blue-blockers had to be worn outside from the end of the night shift until 16:00 h. For circadian assessment, salivary melatonin profiles were obtained between 00:00 h and 08:00 h, before and after 4 experimental night shifts. Sleep was continuously monitored with actigraphy and subjective vigilance was measured at the beginning, the middle and the end of each night and day shifts. The error percentage in wood board classification was used as an index of performance. RESULTS: Through experimental week, melatonin profiles of 3 participants have shifted by at least 2 hours. Improvements were observed in sleep parameters and subjective vigilance from the third night (Wednesday) as performance increased on the fourth night (Thursday) from 5.14% to 1.36% of errors (p=0.04). CONCLUSIONS: Strategic exposure to short wavelengths at night, and/or daytime use of blue-blocker glasses, seemed to improve sleep, vigilance and performance.

Wearing blue-blockers in the morning could improve sleep of workers on a permanent night schedule: a pilot study.

Night shiftworkers often complain of disturbed sleep during the day. This could be partly caused by morning sunlight exposure during the commute home, which tends to maintain the circadian clock on a daytime rhythm. The circadian clock is most sensitive to the blue portion of the visible spectrum, so our aim was to determine if blocking short wavelengths of light below 540 nm could improve daytime sleep quality and nighttime vigilance of night shiftworkers. Eight permanent night shiftworkers (32-56 yrs of age) of Quebec City's Canada Post distribution center were evaluated during summertime, and twenty others (24-55 yrs of age) during fall and winter. Timing, efficacy, and fragmentation of daytime sleep were analyzed over four weeks by a wrist activity monitor, and subjective vigilance was additionally assessed at the end of the night shift in the fall-winter group. The first two weeks served as baseline and the remaining two as experimental weeks when workers had to wear blue-blockers glasses, either just before leaving the workplace at the end of their shift (summer group) or 2 h before the end of the night shift (fall-winter group). They all had to wear the glasses when outside during the day until 16:00 h. When wearing the glasses, workers slept, on average +/-SD, 32+/-29 and 34+/-60 more min/day, increased their sleep efficacy by 1.95+/-2.17% and 4.56+/-6.1%, and lowered their sleep fragmentation by 1.74+/-1.36% and 4.22+/-9.16% in the summer and fall-winter group, respectively. Subjective vigilance also generally improved on Fridays in the fall-winter group. Blue-blockers seem to improve daytime sleep of permanent night-shift workers.

Evidence of a biological effect of light therapy on the retina of patients with seasonal affective disorder.

BACKGROUND: Retinal sensitivity anomalies have been reported in patients affected by seasonal affective disorder (SAD). We used the electroretinogram (ERG) to assess seasonal change in retinal function in patients with SAD and healthy participants, as well as in patients following 4 weeks of light therapy. METHODS: ERG assessments were obtained in 22 SAD patients (2 men, 20 women, mean age 31 +/- 9 years) in the fall/winter season before and after 2 and 4 weeks of light therapy and in summertime. Matched healthy participants (2 men, 14 women; mean age 29 +/- 8 years) were evaluated once in the fall/winter and once in summer. The 29-item Structured Interview Guide for the Hamilton Depression Rating Scale, Seasonal Affective Disorder version was administered. Standard ERG parameters were derived from the photopic and scotopic luminance response functions. Salivary melatonin concentration during ERG was assessed in both groups but during fall/winter assessments only. RESULTS: A significantly lower cone ERG maximal amplitude and lower rod sensitivity was found in SAD patients before light therapy compared with healthy participants. Following 4 weeks of light therapy, a normalization of cone and rod ERG function occurred. ERG parameters in the summer and melatonin concentrations in fall/winter were not significantly different between groups. CONCLUSIONS: Depressed patients with SAD demonstrate ERG changes in the winter compared with healthy comparison subjects with lower rod retinal sensitivity and lower cone maximal amplitude. These changes normalized following 4 weeks of light therapy and during the summer, suggesting that ERG changes are state markers for SAD.

Blue blocker glasses impede the capacity of bright light to suppress melatonin production.

Blocking morning light exposure with dark goggles can contribute to the adjustment to night work but these glasses are incompatible with driving. Recently, it was discovered that the biological clock is most sensitive to short wavelengths (blue light). Therefore, we tested the hypothesis that cutting the blue portion of the light spectrum with orange lens glasses (blue blockers) would prevent the light-induced melatonin suppression, a test broadly used as an indirect assessment of the circadian clock sensitivity. Fourteen normal subjects were exposed at night to a 60 min bright light pulse (1300 lx behind filters) between 01:00 and 02:00 hr while wearing orange lens glasses (experimental condition) or grey lens glasses (control condition). The amount of salivary melatonin change observed during the light pulse was compared with a melatonin baseline obtained the night before. Although both glasses transmitted the same illuminance (1300 lx) but at an irradiance 25% higher for the orange lens (408 microW/cm2) compared with the grey lens (327 microW/cm2), a non-significant increase of 6% (95% CI, -20% to 9%) was observed with the orange lens whereas a significant (P < 0.05) reduction of 46% (95% CI, 35-57%) was observed with the grey lens. Blue blockers represent an elegant means to prevent the light-induced melatonin suppression. Further studies are needed to show that these glasses, which are suitable for driving, could facilitate adaptation to night work.