Changes in Cognitive Performance Are Associated with Changes in Sleep in Older Adults With Insomnia.

The present study examined sleep features associated with cognition in older adults and examined whether sleep changes following insomnia treatment were associated with cognitive improvements. Polysomnography and cognition (recall, working memory, and reasoning) were assessed before and after an insomnia intervention (Brief Behavioral Treatment of Insomnia [BBTI] or information control [IC]) in 77 older adults with insomnia. Baseline wake-after-sleep-onset (WASO) was associated with recall. Greater NREM (nonrapid eye movement) delta power and lower NREM sigma power were associated with greater working memory and reasoning. The insomnia intervention did not improve performance. However, increased absolute delta power and decreased relative sigma power were associated with improved reasoning. Findings suggest that improvements in executive function may occur with changes in NREM architecture.

Subjective-objective sleep discrepancy among older adults: associations with insomnia diagnosis and insomnia treatment.

Discrepancy between subjective and objective measures of sleep is associated with insomnia and increasing age. Cognitive behavioural therapy for insomnia improves sleep quality and decreases subjective-objective sleep discrepancy. This study describes differences between older adults with insomnia and controls in sleep discrepancy, and tests the hypothesis that reduced sleep discrepancy following cognitive behavioural therapy for insomnia correlates with the magnitude of symptom improvement reported by older adults with insomnia. Participants were 63 adults >60 years of age with insomnia, and 51 controls. At baseline, participants completed sleep diaries for 7 days while wearing wrist actigraphs. After receiving cognitive behavioural therapy for insomnia, insomnia patients repeated this sleep assessment. Sleep discrepancy variables were calculated by subtracting actigraphic sleep onset latency and wake after sleep onset from respective self-reported estimates, pre- and post-treatment. Mean level and night-to-night variability in sleep discrepancy were investigated. Baseline sleep discrepancies were compared between groups. Pre-post-treatment changes in Insomnia Severity Index score and sleep discrepancy variables were investigated within older adults with insomnia. Sleep discrepancy was significantly greater and more variable across nights in older adults with insomnia than controls, P ≤ 0.001 for all. Treatment with cognitive behavioural therapy for insomnia was associated with significant reduction in the Insomnia Severity Index score that correlated with changes in mean level and night-to-night variability in wake after sleep onset discrepancy, P < 0.001 for all. Study of sleep discrepancy patterns may guide more targeted treatments for late-life insomnia.

Shiftworkers report worse sleep than day workers, even in retirement.

The aim of this study was to explore how the level of shiftwork exposure during an individual's working life might be related to subjectively reported sleep quality and timing during retirement. Telephone interviews regarding past employment and sleep timing and quality (among other variables) were conducted using a pseudo-random age-targeted sampling process. Subjective sleep quality was assessed using a telephone version of the Pittsburgh Sleep Quality Index. Timing of reported habitual bedtimes and rise-times were assessed using the Sleep Timing Questionnaire. Questions measuring morningness and subjective health were also given. Retired seniors (aged >65 years, n = 1113) were studied. Analysis was by analysis of variance, with shiftwork exposure in three bins [0 (n = 387), 1-15 (n = 371) and >15 years (n = 355)], gender (n = 634 male, 479 female) and former occupation [in two broad categories, 'managerial' (n = 437) versus 'other' (n = 676)] as factors. In retired shiftworkers, relative to retired day workers, past exposure to shiftwork was associated with higher (worse) PSQI scores by 1.0 units (1-15 years) and 0.6 units (>15 years) (main effect P = 0.005). There were also main effects of gender and former occupation (males and managerials reporting better sleep), but neither variable interacted with shiftwork exposure. The timing of current mean habitual bedtimes and rise-times (and also the variance around them) were very similar for the three shiftwork exposure groups. The shiftwork exposure effect did not appear to be mediated by either morningness or current health. Prior exposure to shiftwork would appear to be related to currently reported sleep problems during retirement.

Sleep variability, health-related practices, and inflammatory markers in a community dwelling sample of older adults.

OBJECTIVE: To explore relationships between wake- and sleep-related health behaviors and circulating concentrations of inflammatory markers (interleukin [IL]-6 and tumor necrosis factor [TNF]-α) in a cohort of community dwelling older adults. Low-grade chronic inflammation is an important risk factor for age-related morbidity. Health behaviors, including average aggregate measures of sleep, have been linked to increased inflammation in older adults. Variability in sleep timing may also be associated with increased inflammation. METHOD: Participants were community dwelling older adults ≥ 60 years (n = 222: 39 bereaved, 55 caregivers, 52 with insomnia, and 76 good sleepers). Mean values and intraindividual variability in sleep, as well as caffeine and alcohol use, exercise, and daytime napping, were assessed by sleep diaries. Blood samples were obtained in the morning. RESULTS: Several interactions were noted between sleep behaviors, inflammatory markers, and participant group. Greater variability in wake time and time in bed was associated with higher IL-6 among good sleepers relative to caregivers and older adults with insomnia. Good sleepers who consumed moderate amounts of alcohol had the lowest concentrations of IL-6 compared with the other three groups who consumed alcohol. Insomnia subjects, but not good sleepers, showed increased concentrations of IL-6 associated with caffeine use. Caregivers showed increased concentrations of TNF-α with alcohol use relative to good sleepers. Greater variability in bedtime, later wake times, and longer time in bed was associated with higher TNF-α regardless of group. CONCLUSIONS: Moderation and regularity in the practice of certain health behaviors, including sleep practices, were associated with lower plasma levels of inflammatory markers in older adults. Life circumstances and specific sleep disorders may modify these associations.

A Neurobiological Model of Insomnia.

Insomnia is a common clinical condition resulting in significant costs and morbidity. Previous models of insomnia focusing on psychological and behavioral processes are useful clinically, but lack neurobiological specificity. We propose an insomnia model based on basic and clinical neuroscience findings, and hypothesize that insomnia results from persistent activity in wake-promoting neural structures during NREM sleep. The simultaneous occurrence of sleeping and waking neural activity helps to explain clinical phenomenology and treatment effects in insomnia.

Behavioral circadian regularity at age 1 month predicts anxiety levels during school-age years.

Daily lifestyle regularity is measured using the Social Rhythm Metric (SRM). We developed a Baby SRM, with 59 babies followed for approximately 13years. Baby SRM score at age 1 month significantly predicted the child's school (K-9, 5 time points) anxiety level (more regular=less anxious), and may be mediated through sociability and directed-attention pathways.

Replicable differences in preferred circadian phase between bipolar disorder patients and control individuals.

Morningness/eveningness (M/E) is a stable, quantifiable measure reflecting preferred circadian phase. Two prior studies suggest that bipolar I disorder (BP1) cases are more likely to have lower M/E scores, i.e., be evening types compared with control groups. These studies did not recruit controls systematically and did not evaluate key clinical variables. We sought to replicate the reported associations in a large, well defined sample, while evaluating potential confounding factors. Adults with bipolar disorder (BP) were compared with community controls drawn randomly from the same residential areas (190 cases and 128 controls). M/E was evaluated using the composite scale of morningness (CSM). After accounting for variables correlated with M/E, BP cases had significantly lower CSM scores than controls (i.e., more evening-type or fewer morning-type). There were no significant differences in M/E scores between BP1 or BP2 disorder cases (n=134 and 56, respectively). CSM scores were stable over approximately 2 years in a subgroup of participants (n=52). Individuals prescribed anxiolytic drugs, antidepressants, antipsychotic drugs, mood stabilizers or stimulant drugs had significantly lower age-corrected CSM scores compared with persons not taking these drugs. BP cases are more likely to be evening types, suggesting circadian phase delay in BP cases. Individuals with elevated depressive mood scores are more likely to be evening types. Our results suggest a replicable relationship between circadian phase and morbid mood states.

The Sleep of the Bereaved.

OBJECTIVE: Sleep disruption is common in widow(er)s. The objective of this study was to characterize the sleep of Spousally Bereaved (SB) seniors (60y+) studied within 4-19 months of being widowed. METHOD: Subjective (PSQI, 2-weeks diary) and objective (2-weeks actigraphy) baseline sleep measures were obtained in 47 (38f, 9m) Spousally Bereaved (SB) seniors, 33 (25f, 8m) Good Sleeper Controls (GSC), and 47 (38f, 9m) Older Adults with Insomnia (OAI); each group with the same mean age (72y). OAI subjects passed formal diagnostic criteria for primary or co-morbid insomnia. GSC subjects had no diagnosis of insomnia. At baseline (pre-treatment), all subjects completed 2 weeks of detailed sleep diary and wrist actigraphy, and completed the Pittsburgh Sleep Quality Index (PSQI) among other measures. RESULTS: Significant group effects appeared in PSQI (GSC: 2.4, SB: 6.7, OAI: 10.5; Effect Sizes [ES]>1) and diary measures. In diary measures, for Total Sleep Time, Sleep Efficiency and Wake After Sleep Onset, SB were better than OAI and worse than GSC (0.47

Financial strain is a significant correlate of sleep continuity disturbances in late-life.

Although psychological stress has been associated with disturbed sleep in younger populations, little is known about the stress-sleep relationship in late-life. In the present study, we evaluated relationships among a chronic stressor, ongoing financial strain, and sleep in a heterogenous sample (n=75) of community-dwelling elders (mean age=74.0 years). Self-report measures included ongoing financial strain, mental health, physical health and subjective sleep quality. Sleep duration, continuity, and architecture were measured by polysomnography (PSG). Analysis of variance and regression were used to test the hypothesis that ongoing financial strain is a significant correlate of disturbed sleep in the elderly. Covariates included age, sex, mental health and physical health. Analyses revealed that ongoing financial strain is a significant correlate of PSG-assessed sleep latency, wakefulness after sleep onset, and sleep efficiency. After adjusting for the effects of age, sex, mental health, and physical health on sleep, ongoing financial strain was associated with lower sleep efficiency (p<.01). Our results show that chronic stress, as measured by ongoing financial strain, is a significant correlate of sleep disturbances in the elderly, even after adjusting for factors known to impact sleep in late-life.

Sleep and circadian rhythms in spousally bereaved seniors.

A laboratory study of sleep and circadian rhythms was undertaken in 28 spousally bereaved seniors (> or =60 yrs) at least four months after the loss event. Measures taken included two nights of polysomnography (second night used), approximately 36 h of continuous core body temperature monitoring, and four assessments of mood and alertness throughout a day. Preceding the laboratory study, two-week diaries were completed, allowing the assessment of lifestyle regularity using the 17-item Social Rhythm Metric (SRM) and the timing of sleep using the Pittsburgh Sleep Diary (PghSD). Also completed were questionnaires assessing level of grief (Texas Revised Inventory of Grief [TRIG] and Index of Complicated Grief [ICG]), subjective sleep quality (Pittsburgh Sleep Quality Index [PSQI]), morningness-eveningness (Composite Scale of Morningness [CSM]), and clinical interview yielding a Hamilton Depression Rating Scale (HDRS) score. Grief was still present, as indicated by an average TRIG score of about 60. On average, the bereaved seniors habitually slept between approximately 23:00 and approximately 06:40 h, achieving approximately 6 h of sleep with a sleep efficiency of approximately 80%. They took about 30 min to fall asleep, and had their first REM episode after 75 min. About 20% of their sleep was in Stage REM, and about 3% in Stages 3 or 4 (slow wave sleep). Their mean PSQI score was 6.4. Their circadian temperature rhythms showed the usual classic shape with a trough at approximately 01:00 h, a fairly steep rise through the morning hours, and a more gradual rise to mid-evening, with an amplitude of approximately 0.8 degrees C. In terms of lifestyle regularity, the mean regularity (SRM) score was 3.65 (slightly lower than that usually seen in seniors). Mood and alertness showed time-of-day variation with peak alertness in the late morning and peak mood in the afternoon. Correlations between outcome sleep/circadian variables and level of grief (TRIG score) were calculated; there was a slight trend for higher grief to be associated with less time spent asleep (p=0.07) and reduced alertness at 20:00 h (p=0.05). Depression score was not correlated with TRIG score (p>0.20). When subjects were divided into groups by the nature of their late spouse's death (expected/after a long-term chronic illness [n=18] versus unexpected [n=10]), no differences emerged in any of the variables. In conclusion, when studied at least four months after the loss event, there appears to be some sleep disruption in spousally bereaved seniors. However, this disruption does not appear to be due to bereavement-related disruptions in the circadian system.

Personality correlates with sleep-wake variables.

A mail-in questionnaire study and two confirmatory archival analyses are described. Variables related to personality and measures of sleep timing, sleep quality, and sleep duration were initially assessed by self-report in a sample of 54 working adults (31.5% male, 23-48 yrs). Extraversion and neuroticism were measured by the Eysenck Personality Inventory (EPI), and the level of sub-clinical manic-type symptoms by the Attitude to Life Questionnaire (ATLQ). The quality of sleep was measured by the Pittsburgh Sleep Quality Index (PSQI) and by questions relating to habitual sleep latency and minutes awake after sleep onset from the Sleep Timing Questionnaire (STQ). The duration and timing of sleep was assessed using the STQ separately for work-week nights (Sunday-Thursday) and for weekend nights (Friday and Saturday). Morningness-eveningness was assessed using the Composite Scale of Morningness (CSM). Two confirmatory analyses using separate archival samples (Study A: n=201, 55.7% male, 20-57 yrs; Study B: n=101, 47.5% male, 18-59 yrs) were then used to confirm specific correlations of interest. In both initial and confirmatory studies, increased sub-clinical manic-type symptoms were found to be significantly associated with later bedtimes and wake-times during the work-week and lower (more evening-type) CSM scores, and higher neuroticism was associated with poorer sleep as indicated by higher PSQI scores. In contrast, no significant correlations emerged between any of the personality variables and any of the sleep duration variables. Personality appears to affect certain aspects of the timing and subjective quality of sleep, but not necessarily its duration.

Associations between period 3 gene polymorphisms and sleep- /chronotype-related variables in patients with late-life insomnia.

A variable number tandem repeat polymorphism (VNTR) in the period 3 (PER3) gene has been associated with heritable sleep and circadian variables, including self-rated chronotypes, polysomnographic (PSG) variables, insomnia and circadian sleep-wake disorders. This report describes novel molecular and clinical analyses of PER3 VNTR polymorphisms to better define their functional consequences. As the PER3 VNTR is located in the exonic (protein coding) region of PER3, we initially investigated whether both alleles (variants) are transcribed into messenger RNA in human fibroblasts. The VNTR showed bi-allelic gene expression. We next investigated genetic associations in relation to clinical variables in 274 older adult Caucasian individuals. Independent variables included genotypes for the PER3 VNTR as well as a representative set of single nucleotide polymorphisms (SNPs) that tag common variants at the PER3 locus (linkage disequilibrium (LD) between genetic variants < 0.5). In order to comprehensively evaluate variables analyzed individually in prior analyses, dependent measures included PSG total sleep time and sleep latency, self-rated chronotype, estimated with the Composite Scale (CS), and lifestyle regularity, estimated using the social rhythm metric (SRM). Initially, genetic polymorphisms were individually analyzed in relation to each outcome variable using analysis of variance (ANOVA). Nominally significant associations were further tested using regression analyses that incorporated individual ANOVA-associated DNA variants as potential predictors and each of the selected sleep/circadian variables as outcomes. The covariates included age, gender, body mass index and an index of medical co-morbidity. Significant genetic associations with the VNTR were not detected with the sleep or circadian variables. Nominally significant associations were detected between SNP rs1012477 and CS scores (p = 0.003) and between rs10462021 and SRM (p = 0.047); rs11579477 and average delta power (p = 0.043) (analyses uncorrected for multiple comparisons). In conclusion, alleles of the VNTR are expressed at the transcript level and may have a functional effect in cells expressing the PER3 gene. PER3 polymorphisms had a modest impact on selected sleep/circadian variables in our sample, suggesting that PER3 is associated with sleep and circadian function beyond VNTR polymorphisms. Further replicate analyses in larger, independent samples are recommended.

Task switching in older adults with and without insomnia.

BACKGROUND: Task-switching deficits are common in older adults and in those with insomnia. Such deficits may be driven by difficulties with sleep continuity and dampened homeostatic sleep drive. OBJECTIVE: To identify the aspects of task switching affected by insomnia and its treatment, and to determine whether such effects are associated with sleep continuity and homeostatic sleep drive. METHODS: Polysomnographic sleep and task switching were tested in healthy older adults aged 60-93 years with insomnia (n = 48) and normal sleeping controls (n = 51). Assessments were repeated in the insomnia group after eight weeks of cognitive behavioral treatment for insomnia. Sleep measures included wake after sleep onset (WASO) and quantitative indices of homeostatic sleep drive (delta power during nonrapid eye movement [NREM] sleep and the ratio of delta power during the first and second NREM periods). A cued task-switching paradigm instructed participants to perform one of two tasks with varying preparatory cue-target intervals, manipulating task alternation, task repetition, and task preparation. RESULTS: The effect of preparatory cues on accuracy was diminished in the insomnia group compared with that in controls. Across the two groups, a stronger effect of preparatory cues was associated with a higher delta sleep ratio. Following insomnia treatment, task-repetition accuracy significantly improved. This improvement was associated with improvements in WASO. There were no group or treatment effects on response time or task alternation accuracy. CONCLUSIONS: Effects of insomnia diagnosis and treatment apply to conditions that depend on the maintenance of a task set, rather than a domain general effect across task switching. Such effects are associated with homeostatic sleep drive and sleep continuity.

Age-related differences in the lifestyle regularity of seniors experiencing bereavement, care-giving, insomnia, and advancement into old-old age.

Compared to younger adults, seniors (> or = 60 yrs) often adopt a highly regular lifestyle, perhaps as an adaptive response to age-related changes in their sleep and circadian rhythms. At baseline, diary measures of lifestyle regularity (SRM-5) were obtained from 104 seniors of three separate groups. Thirty-three subjects were challenged by spousal bereavement or the need to care for a spouse at home with dementia (Challenged); 33 were suffering from formally diagnosed (DSM-IV) insomnia (Insomnia); and 38 were healthy, well-functioning older seniors in the second half of their eighth decade of life or later (Healthy Older). The objective of this study was to determine whether lifestyle regularity increased as a function of age within each of these three senior groups. Overall, age was significantly correlated with SRM-5 (r=0.41, p<0.001), with the SRM score increasing by 0.67 units/decade. The same was true for the Challenged and Insomnia groups, which also showed a significant correlation between SRM and age (Challenged: r=0.48, p<0.01; Insomnia: r=0.36, p<0.05), though with a slightly faster rate of SRM increase in the Challenged (0.95 units/decade) than Insomnia (0.55 units/decade) group. Perhaps there was no correlation between age and SRM (r=0.07, n.s.) in the Healthy Older group due to the small age range, although this group did have a higher overall SRM score than the other two groups (p<0.01). The study thus confirmed that the previously observed increase in lifestyle regularity over the adult lifespan persists into later life. This may represent an adaptive behavioral response that might be used in future therapeutic approaches.

Using daily 30-min phase advances to achieve a 6-hour advance: circadian rhythm, sleep, and alertness.

INTRODUCTION: A ground-based study was undertaken to determine whether circadian and sleep dysfunction could be avoided by "trickling in" a 6-h phase advance in sleep/wake schedule by 12 consecutive 30-min phase advances as per NASA's Appendix K. METHODS: We simulated a 16-d (384 h) mission for each of 10 subjects. Temporal cues and light levels approximated those experienced in space. All sleep periods were exactly 8 h. Before the study, for 14 d, subjects were required to live on a schedule with a 23:00 bedtime and 07:00 wake time. Laboratory sessions then started with a 4-d baseline segment on that schedule. The fourth night and the day following it were then taken as baseline. Repeated 30-min phase advances in bedtime were then required on each of the next 12 successive nights, resulting in an eventual movement of bedtimes to a 6-h phase-advanced position (bedtime: 17:00, wake time: 01:00). Polysomnographic sleep, circadian rhythms in urinary free cortisol, urinary volume (every void), and core body temperature (once per minute), and ratings of performance, mood, and alertness (five per day) were measured. RESULTS: While circadian dysfunction was largely avoided by trickling in the phase shift, there remained slight differences in phase between the endogenous circadian pacemaker and the imposed routine which disrupted sleep and daytime alertness. CONCLUSION: Though statistically significant, the disruption was less than we observed from repeated 2-h phase delays reported in a 2004 ASEM paper. Evidence would thus seem to favor repeated 30-min phase advances over repeated 2-h phase delays.

Aging human circadian rhythms: conventional wisdom may not always be right.

This review discusses the ways in which the circadian rhythms of older people are different from those of younger adults. After a brief discussion of clinical issues, the review describes the conventional wisdom regarding age-related changes in circadian rhythms. These can be summarized as four assertions regarding what happens to people as they get older: 1) the amplitude of their circadian rhythms reduces, 2) the phase of their circadian rhythms becomes earlier, 3) their natural free-running period (tau) shortens, and 4) their ability to tolerate abrupt phase shifts (e.g., from jet travel or night work) worsens. The review then discusses the empirical evidence for and against these assertions and discusses some alternative explanations. The conclusions are that although older people undoubtedly have earlier circadian phases than younger adults, and have more trouble coping with shift work and jet lag, evidence for the assertions about rhythm amplitude and tau are, at best, mixed.

Circadian patterns of sleep, sleepiness, and performance in older and younger adults.

STUDY OBJECTIVE: To compare circadian patterns of sleep, subjective sleepiness, and psychomotor performance in older and younger adults. DESIGN: Controlled experimental laboratory study. SETTING: General Clinical Research Center. PARTICIPANTS: Healthy older adults (n = 17, mean age 76 years) and healthy younger adults (n = 19, mean age 23 years). INTERVENTIONS: Subjects lived for 60 consecutive hours on a 90-minute sleep-wake cycle (30 minutes in bed, 60 minutes awake). Electroencephalographic recordings were conducted during bedrest periods. Self-ratings and psychomotor performance tests were conducted during 60-minute wake periods. MEASUREMENTS AND RESULTS: Data were analyzed with cosinor and linear mixed models. Amplitude and phase of the core body temperature rhythm did not significantly differ by age group. Older adults had significantly reduced mean levels and amplitude of rhythms in total sleep time and sleep efficiency and increased mean levels and amplitude of rhythms in sleep latency and wake after sleep onset. Age groups did not differ in mean level of subjective sleepiness, but older adults had reduced amplitude. Older adults had worse overall psychomotor performance, with evidence of larger circadian amplitude in some of these rhythms. Age groups did not differ on the phase position of any rhythm. CONCLUSIONS: Older adults had a lower level and smaller circadian variation of sleep propensity compared with younger adults, whereas wakefulness and psychomotor performance rhythms tended to show increased circadian variation among older subjects. These findings likely result from a combination of age-related changes in cortical function, homeostatic sleep mechanisms, and circadian regulation.

Circadian phase variation in bipolar I disorder.

Abnormalities in circadian rhythms are prominent features of bipolar I disorder (BD1). To investigate circadian variation in BD1, we evaluated morningness-eveningness (M/E), a stable trait reflecting circadian phase, using the composite scale (CS) among BD1 patients (DSM IV criteria; n = 75), unscreened controls (n = 349), and patients with schizophrenia (SZ) or schizoaffective disorder (SZA) (n = 81). Our analyses showed that CS scores correlated significantly with age but did not differ by gender among the controls. BD1 patients differed significantly from controls and from SZ/SZA patients when age was considered. CS scores were distributed bi-modally among BD1 cases. There are several possible reasons for the observed heterogeneity. Younger BD1 patients, and those with rapid mood swings, were significantly more likely to have lower CS scores (i.e., to score in the 'evening' range and to have later circadian phase). CS scores were also positively correlated with the age at onset and the duration of the most severe depressive episodes. These relationships were not observed among the SZ/SZA groups. Thus, distinct patterns of M/E were noted among BD1 patients and among BD1 subgroups. The impact of medication, mood state, and chronicity on CS scores needs to be considered.

Heritability of morningness-eveningness and self-report sleep measures in a family-based sample of 521 hutterites.

Individual variation in the phase and amplitude of human circadian rhythms is well known, but the impact of heritable factors on such variation is less clear. We estimated the narrow-sense heritability for selected circadian and sleep timing, quality, and duration measures among related members of the Hutterites, an endogamous, religious community (n=521 participants). "Morningness-eveningness" (M/E), a stable trait reflecting circadian phase, was evaluated using the Composite Scale (CS). Subjective sleep measures were assessed using the Sleep Timing Questionnaire. Initial analyses reconfirmed the impact of age on M/E. Previously reported correlations between M/E scores and the sleep measures were also noted, demonstrating the construct validity of the questionnaires among the participants. Following corrections for age, gender, and colony of residence, significant narrow-sense heritability was noted for M/E (23%). The heritability for subjective sleep measures (related to timing, duration, and quality) were statistically significant for all but one variable, and varied between 12.4% and 29.4%. Thus, significant heritable influences on human circadian phase and subjective sleep indices can be detected through family-based studies. In view of the impact of circadian malfunction on human health, it may be worthwhile to map genetic factors impacting circadian and sleep variation.