All light is not equal: blue wavelengths are the most potent portion of the visible electromagnetic spectrum for circadian regulation. Therefore, blocking blue light could create a form of physiologic darkness. Because the timing and quantity of light and darkness both affect sleep, evening use of amber lenses to block blue light might affect sleep quality. Mood is also affected by light and sleep; therefore, mood might be affected by blue light blockade. In this study, 20 adult volunteers were randomized to wear either blue-blocking (amber) or yellow-tinted (blocking ultraviolet only) safety glasses for 3 h prior to sleep. Participants completed sleep diaries during a one-week baseline assessment and two weeks' use of glasses. Outcome measures were subjective: change in overall sleep quality and positive/negative affect. Results demonstrated that sleep quality at study outset was poorer in the amber lens than the control group. Two- by three-way ANOVA revealed significant (p<.001) interaction between quality of sleep over the three weeks and experimental condition. At the end of the study, the amber lens group experienced significant (p<.001) improvement in sleep quality relative to the control group and positive affect (p = .005). Mood also improved significantly relative to controls. A replication with more detailed data on the subjects' circadian baseline and objective outcome measures is warranted.

RATIONALE:An increasing body of evidence links the occurrence of sleep continuity disturbances with increased inflammation and both sleep disturbances and inflammation are associated with clinical depression. Typhoid vaccination results in a mild inflammatory response that significantly increases levels of the proinflammatory cytokine, interleukin (IL)-6.

OBJECTIVES:The present exploratory study aimed to enhance our understanding of the link between inflammation, sleep and depression by examining the effects of typhoid vaccine on the sleep polysomnogram.

METHODS:We studied the effects of a single injection of typhoid polysaccharide vaccine and placebo (saline solution) on sleep in 16 healthy male and female participants aged 20-38 years, sleeping at home in a randomized, double-blind, balanced order, crossover design. Subjective measures of mood, sleep and adverse effects were elicited and plasma samples analysed for IL-6 levels.

RESULTS:IL-6 levels (in picogramme per millilitre) significantly increased 2 h post vaccine compared to placebo (0.90 vs 0.53, p = 0.026, r = 0.55). Relative to placebo, typhoid vaccination produced significant impairment in several measures of sleep continuity. Total sleep time (in minute) (426.1 vs 410.7, p = 0.005, r = 0.62) and sleep efficiency percent (94.3 vs91.5, p = 0.007, r = 0.65) were decreased; with increases in wake after sleep onset (in minute) (25.5 vs 38.8, p = 0.007,r = 0.65), total wake (in minute) (34.9 vs 50.3, p = 0.005,r = 0.67), sleep stage transitions (155.9 vs 173.1, p = 0.026, r = 0.56), number of awakenings (27.2 vs36.1, p = 0.007, r = 0.64) and awakening index (3.8 vs 5.3, p = 0.005, r = 0.67) (means, significance level and effect size).

CONCLUSIONS:Inflammatory mechanisms may underlie the impairment in sleep efficiency which is a hallmark of major depression. Because impaired sleep is also a predictor of major depression, there may be a role for suitable anti-inflammatory approaches in strategies designed to prevent the onset of depression. ClinicalTrials.gov ( https://www.clinicaltrials.gov ): NCT02628054.

Aging is associated with an earlier timing of circadian rhythms and a shorter phase angle between wake time and the timing of melatonin secretion or the core body temperature nadir. Light has a phase-dependent effect on the circadian pacemaker, and modifications of habitual light exposure in older people could contribute to a change in the timing of circadian rhythms or in the phase angle of entrainment. In this study, we compare natural light exposure of community-dwelling older and young subjects studied at the same time of year, focusing on the pattern of light exposure across the waking day. We recorded light exposure data for 3 to 8 days from 22 older (aged 66.01 +/- 5.83) and 22 young subjects (aged 23.41 +/- 4.57), living at home on self-selected sleepwake schedules, and matched for time of year. All subjects were from New England (latitude 42.3 degrees N to 43 degrees N). We compared the percentage of the waking day spent by older and young subjects at 4 different light levels (from very dim to very bright). We compared hourly averaged light exposure data in each group according to clock time and with respect to each subject's daily sleepwake times. Although both age groups spent more than half of their waking hours in dim or moderate room light intensity (<100 lux), we found that the older subjects spent a significantly greater percentage of their waking day in the brighter light levels (>or =1000 lux); their hourly averaged light exposure levels were also significantly greater whether we examined the data with respect to absolute clock time, to wake time, or to bed time, and this was true across all seasons. We found that healthy older people were exposed to significantly higher levels of light throughout their waking day than young people. Differences in natural light exposure may contribute to the age-related phase advance of the circadian pacemaker and its later timing relative to the sleepwake cycle. This hypothesis should be explored further in carefully designed prospective studies.