Biomedical subjects

Shawn D Youngstedt

Publications and source records attributed to Shawn D Youngstedt.

14 recordsLinked to original sources

PubMed2006

Circadian variation in swim performance.

Previous findings of time-of-day differences in athletic performance could be confounded by diurnal fluctuations in environmental and behavioral "masking" factors (e.g., sleep, ambient temperature, and energy intake). The purpose of this study was to examine whether there is a circadian rhythm in swim performance that is independent of these masking factors. Experienced swimmers (n = 25) were assessed for 50-55 consecutive hours in the laboratory. The swimmers followed a 3-h "ultra-short" sleep-wake cycle, involving 1 h of sleep in darkness and 2 h of wakefulness in dim light, that was repeated throughout the observation. The protocol distributes behavioral and environmental masking factors equally across the 24-h period. Each swimmer was scheduled to perform six maximal-effort 200-m swim trials that were distributed equally across eight times of day (n = 147 trials). Each trial was separated by 9 h. A cosine fit of intra-aural temperature data established the time of the lowest body temperature (Tmin). Swim performances were z-transformed and compared across the eight times of day and across twelve 2-h intervals relative to Tmin. Analysis of covariance, controlling for trial number, revealed a significant (P < 0.001) pattern in swim performance relative to environmental and circadian times of day. Performance peaked 5-7 h before Tmin (approximately 2300) and was worst from 1 h before to 1 h after Tmin (approximately 0500). Mean swim performance was 169.5 s; circadian variation from peak to worst performance was 5.8 s. These data suggest a circadian rhythm in athletic performance independent of environmental and behavioral masking effects.

Adult↗

PubMed2005

Circadian phase-shifting effects of a laboratory environment: a clinical trial with bright and dim light.

BACKGROUND: Our aims were to examine the influence of different bright light schedules on mood, sleep, and circadian organization in older adults (n = 60, ages 60-79 years) with insomnia and/or depression, contrasting with responses of young, healthy controls (n = 30, ages 20-40 years). METHODS: Volunteers were assessed for one week in their home environments. Urine was collected over two 24-hour periods to establish baseline acrophase of 6-sulphatoxymelatonin (aMT6s) excretion. Immediately following home recording, volunteers spent five nights and four days in the laboratory. Sleep periods were fixed at eight hours in darkness, consistent with the volunteers' usual sleep periods. Volunteers were randomly assigned to one of three light treatments (four hours per day) within the wake period: (A) two hours of 3,000 lux at 1-3 hours and 13-15 hours after arising; (B) four hours of 3,000 lux at 6-10 hours after arising; (C) four hours of dim placebo light at 6-10 hours after arising. Lighting was 50 lux during the remainder of wakefulness. The resulting aMT6s acrophase was determined during the final 30 hours in the laboratory. RESULTS: Neither mood nor total melatonin excretion differed significantly by treatment. For the three light treatments, significant and similar phase-response plots were found, indicating that the shift in aMT6s acrophase was dependent upon the circadian time of treatment. The changes in circadian timing were not significantly correlated to changes in sleep or mood. CONCLUSION: The trial failed to demonstrate photoperiodic effects. The results suggest that even low levels of illumination and/or fixed timing of behavior had significant phase-shifting effects.

Journal Article↗

PubMed2005

Effects of exercise on sleep.

Historically, perhaps no daytime behavior has been more closely associated with better sleep than exercise. The assumption that exercise promotes sleep has also been central to various hypotheses about the functions of sleep. Hypotheses that sleep serves an energy conservation function, a body tissue restitution function, or a temperature down-regulation function all have predicted a uniquely potent effect of exercise on sleep because no other stimulus elicits greater depletion of energy stores, tissue breakdown, or elevation of body temperature, respectively. Exercise offers a potentially attractive alternative or adjuvant treatment for insomnia. Sleeping pills have a number of adverse side effects and are not recommended for long-term use, partly on the basis of a significant epidemiologic association of chronic hypnotic use with mortality. Other behavioral/cognitive treatments are more effective for chronic insomnia treatment, but difficult and costly to deliver. By contrast, exercise could be a healthy, safe, inexpensive, and simple means of improving sleep.

Anxiety↗

PubMed2004

Long sleep and mortality: rationale for sleep restriction.

Epidemiologic studies have consistently shown that sleeping >8 h per night is associated with increased mortality. Indeed, the most recent American Cancer Society data of 1.1 million respondents showed that sleeping longer than 7.5 h was associated with approximately 5% of the total mortality of the sample. The excess mortality was found even after controlling for 32 potentially confounding risk factors. Although epidemiologic data cannot prove that long sleep duration causes mortality, there is sufficient evidence to warrant future testing of the hypothesis that mild sleep restriction would decrease mortality in long sleepers. Sleep restriction might resemble dietary restriction as a potential aid to survival. Sleep restriction has several potential benefits besides possible enhanced survival. Acute sleep restriction can have dramatic antidepressant effects. Also, chronic sleep restriction is perhaps the most effective treatment for primary insomnia. Conversely, spending excessive time in bed can elicit daytime lethargy and exacerbate sleep fragmentation, resulting in a vicious cycle of further time in bed and further sleep fragmentation. Sleep restriction may be most beneficial for older adults, who tend to spend excessive time in bed and have more sleep fragmentation compared with young adults.

Aging↗

PubMed2003

Melatonin excretion with affect disorders over age 60.

Numerous studies have reported low melatonin secretion in depression, but other studies have suggested no deficit or an increase. Alterations of circadian phase or duration of melatonin secretion have also been described. Since melatonin secretion decreases as we age, it seemed interesting to examine melatonin and depression in an aging sample. Volunteers who complained of mood or sleep problems were recruited for studies in which fractional urine specimens were collected for 24 h, both at home and in the laboratory. The major metabolite, 6-sulfatoxymelatonin (aMT6s), was determined by radioimmunoassay. Of 72 volunteers aged 60-78 years, seven had current major depression and 55% had a lifetime history of an affective disorder. A 55-fold range of home aMT6s excretion rates was observed. A lifetime history of any affective disorder was significantly associated with greater log(10)[mesor] aMT6s excretion in home collections and laboratory collections, but current affective disorders were neither significantly related to melatonin excretion nor to aMT6s acrophase timing, onset, offset or duration. These results are only weakly consistent with a photoperiodic hypothesis of depression.

Aged↗

PubMed2003

Luteinizing hormone following light exposure in healthy young men.

Urinary luteinizing hormone (LH) and the melatonin metabolite (6-sulfatoxymelatonin; aMT6s) were measured in normal young men following early morning light exposure. Eleven young healthy men ages 19-30 years participated in this study. During separate weeks in counterbalanced order, each subject received both 5 days of bright light treatment (BL) and 5 days of placebo light treatment (PL) for 1 h (05:00-06:00). LH excretion was increased 69.5% after bright light exposure, but was not changed by placebo light exposure. The acrophases and offsets of aMT6s were advanced, but the duration of aMT6s excretion was not changed after BL. Light stimulation of LH could have interesting applications in psychiatry and reproductive endocrinology.

Adult↗

PubMed2003

No association of sleep with total daily physical activity in normal sleepers.

The aim of two studies was to examine both between-subjects and within-subjects associations between daily amounts of physical activity and sleep in the home environment. Study 1 examined self-reported exercise durations and sleep diaries for 105 consecutive days in 31 college students who were normal sleepers. Between-subjects associations of mean exercise with mean sleep were assessed with Spearman rank-order correlations. Within-subjects correlations were determined across 105 days, and by comparing sleep on the 11 most active vs. the 11 least active days. Study 2 examined 71 physically active adults (n=38 ages 18-30 years, and n=33 ages 60-75 years), the majority of whom were normal sleepers. Over seven consecutive days, physical activity was assessed via actigraphy and a diary-derived estimate of energy expenditure, and sleep was assessed via actigraphy and sleep diaries. Between-subjects associations of mean physical activity with mean sleep were assessed with partial correlations, controlling for age. Within-subjects associations were assessed with ANCOVAs, with daily physical activity serving as the covariate, and by comparing sleep on the most active vs. the least active day. No significant within-subjects associations between physical activity and sleep were found in the main analyses of either study. Two small, but significant, between-subjects correlations between different physical activity measures and subjective sleep were found in Study 2. These results fail to support epidemiologic data on the value of exercise for sleep, but are consistent with experimental evidence showing only modest effects of exercise on sleep.

Adolescent↗

PubMed2003

Actigraphy suggests age-related differences in napping and nocturnal sleep.

The aim of this study was to contrast the time distribution of out-of-bed napping in young and older adults through recordings of wrist activity, and to evaluate the correlates of napping with nocturnal sleep. Seventy-three young adults between 18 and 32 years and 60 older adults between 60 and 75 years of age participated in the study. Subjects were selected for good general health and had few sleep complaints. They wore wrist-activity monitors and kept daily sleep logs for 1 week. Automatic sleep scoring was edited by the authors, supplemented by sleep logs and illumination data as well as activity data. Napping episodes were modestly increased in older adults, but there was no difference in the daily duration of napping. Older adults napped more in the evening (especially within 2 h before bedtime), whereas young adults napped more in the afternoon. The older adults with evening naps (n = 31) showed earlier nocturnal wake-up times and decreased nocturnal sleep duration compared with the older adults without evening naps (n = 29). There was no difference in nocturnal sleep between young adults with afternoon naps (n = 32) and without afternoon naps (n = 41). In determining the effects of napping on nocturnal sleep, timing of napping and age are important. Maintaining alertness during the evening (e.g. by bright light exposure or moderate exercise) would be a possible approach to delay wake-up times in older adults.

Adolescent↗

PubMed2003

Age-related changes of circadian rhythms and sleep-wake cycles.

OBJECTIVES: To compare relationships between the sleep-wake cycle and endogenous circadian rhythms in young and older adults and to examine correlates between evening naps and circadian rhythms in older adults. DESIGN: For 1 week of home recording, subjects wore wrist-activity monitors and kept daily sleep logs. After the home monitoring, subjects entered the laboratory on a 90-minute sleep-wake schedule and were monitored on this schedule for at least 30 hours. SETTING: Community living and laboratory. PARTICIPANTS: Sixty-seven young adults, aged 18 to 32, and 56 older adults, aged 60 to 75, who were healthy and had few sleep complaints. MEASUREMENTS: Times of nocturnal sleep, out-of-bed napping, and illumination were obtained at home. Sleep propensity and oral body temperature (OBT) were measured in the laboratory, along with circadian rhythms of cortisol and 6-sulfatoxymelatonin (aMT6s, assayed from urine samples collected every 90 minutes). RESULTS: Home sleep times and illumination acrophases (fitted peak times) were advanced in older adults. The phase angles (time intervals) between onset of aMT6s and sleep onset were not changed in older adults, but sleep offset was more advanced than acrophase and offset of aMT6s with aging. Acrophases of cortisol and sleep propensity were advanced in older adults to the same extent as sleep times, but OBT was less advanced than sleep times. Older adults who took evening naps showed more advanced sleep offset and circadian rhythms of aMT6s, but there were no differences in the phase angles of sleep onset and circadian rhythms of aMT6s and cortisol compared with older adults who did not take evening naps. CONCLUSION: Measuring different circadian markers suggested different phase relationships between the sleep-wake cycle and endogenous circadian rhythms in aging. Early awakening in older adults cannot be explained simply by a relative phase advance of the circadian system. Evening naps and advanced illumination may play a role in the advance of the circadian system in aging.

Adolescent↗

PubMed2003

Ceiling and floor effects in sleep research.

Ceiling and floor effects dictate that the efficacy of sleep-promoting stimuli should be proportional to the degree of pre-stimulus sleep impairment. This review addressed CF effects in polysomnographic research involving hypnotic drugs and exercise. Correlations of placebo/baseline levels of sleep with changes in sleep following hypnotic or exercise treatment were assessed across both literatures. CF effects were further addressed by comparing sleep-promoting effects of hypnotics vs exercise, after ANCOVA control for substantial baseline differences reported in studies of these stimuli. Significant correlations between placebo-baseline levels and sleep changes were observed following both hypnotic and exercise stimuli. Indeed, approximately 60% of the variance in improvement in sleep latency (SOL), wakefulness after sleep onset (WASO) and total sleep time (TST) following hypnotic treatment was associated with differences in baseline levels. ANCOVAs revealed significantly greater decreases in SOL and WASO following hypnotics compared with exercise. However, no significant difference between stimuli was found for TST, and exercise elicited a significantly greater increase in slow wave sleep. Similar results were found when a comparison between hypnotics and exercise was limited to good sleepers. The results show powerful CF influences on sleep responses to hypnotics and exercise and suggest a need for comparing these treatments in poor sleepers.

Exercise↗

PubMed2003

PRC bisection tests.

This communication presents a new method for evaluating phase response curves (PRCs). A PRC describes the phase shifts produced in an oscillator by stimuli applied at different initial phase-states of that oscillator. In the PRC bisection tests, we repeatedly cut in half the circular distribution of the initial phase-states of the oscillator when stimuli are given. Empirically, we locate that optimal diameter which best bisects the circular distribution of phase responses into arcs of relative phase advance and phase delay. We compute a D score reflecting the success of the best bisection. The null hypothesis of a random distribution of phase responses by initial phase is tested with a Monte Carlo procedure, which computes Dr scores from random combinations of phase shifts with initial phases, thus determining the probability, given the null hypothesis, that the observed D score was from a random distribution. The bisection procedure can be extended to examine whether stronger phase shifts are produced in one phase response curve than in contrasting curves. Also, the bisection procedure yields an estimate of the inflection point of the phase response curve. A method is given to estimate the power of the PRC bisection test.

Animals↗

PubMed2002

No association of 6-sulfatoxymelatonin with in-bed 60-Hz magnetic field exposure or illumination level among older adults.

We examined the association of 6-sulfatoxymelatonin (aMT6s) excretion with in-bed 60-Hz magnetic field (MF) exposure and other potential regulators. Adults aged 50-81 years (n=242 years, mean 67.6+/-5.7 years) were monitored for 1 week in their home environments. Mean and maximum MF exposure were assessed with EMDEX Lite instruments. Illumination mesor, amplitude, and acrophase (peak time) were determined from 24-h Actillume wrist monitors. Other regulators of aMT6s assessed were age, usage of melatonin-altering medications, and day length. During two 24-h intervals, all urine voidings were collected. The mesor, amplitude, and acrophase of aMT6s excretion were determined. Multiple regression analyses revealed no association between MF and aMT6s. Medication usage was associated with significantly lower aMT6s mesor and amplitude. Illumination acrophase and amplitude were significantly associated with aMT6s acrophase. These data suggest no influence of nocturnal environmental MF exposure on aMT6s excretion in older adults.

Aged↗

PubMed2002

Illumination of upper and middle visual fields produces equivalent suppression of melatonin in older volunteers.

Bright light treatment has become an important method of treating depression and circadian rhythm sleep disorders. The efficacy of bright light treatment may be dependent upon the position of the light-source, as it determines the relative illumination in each portion of the visual field. This study compared illumination of upper and middle visual fields to determine whether melatonin suppression is different or equivalent. Thirteen older volunteers received three illumination conditions in counterbalanced orders: 1000 lux in the upper visual field, 1000 lux in the middle visual field, or dim diffuse illumination < 5 lux. A four-choice reaction time task was performed during tests to ensure eye direction and illumination of the intended portion of the visual field. Illumination in the upper and middle visual fields significantly suppressed melatonin compared to < 5 lux (p < 0.001). Melatonin suppression was not significantly different with upper or middle field illumination. These results indicate that bright light treatments placed above the eye level might be as effective as those requiring patients to look directly at the light source. Clinical comparative testing would be valuable. In addition, this study demonstrates that significant suppression of melatonin may be achieved through the use of bright light in healthy older volunteers.

Aged↗

PubMed2002

Circadian phase-delaying effects of bright light alone and combined with exercise in humans.

In a within-subjects (n = 18), counterbalanced design, the circadian phase-shifting effects of 3 h of 1) bright light (3,000 lx) alone 2) and bright light combined with vigorous exercise were compared. For each treatment, volunteers spent 3 nights and 2 days in the laboratory, typically receiving the treatment from approximately 2300 to 0200 on night 2. Bedtimes and waketimes were fixed to the volunteers' habits. Illumination was 50 lx during other wake hours and 0 lx during sleep. Bright Light Alone elicited a significant phase delay in rectal temperature minimum (70 min), but not in urinary 6-sulphatoxymelatonin (6-SMT) acrophase (20 min). Bright Light + Exercise elicited a significant phase delay in 6-SMT (68 min), but did not result in a significant difference in shift compared with Bright Light Alone. The study had adequate statistical power (80%) to detect phase-shift differences between treatments of approximately 2-2.5 h. Thus any antagonism of light shifts with exercise could not have been revealed. Within the limited exercise and light parameters of this study, the results suggest that exercise does not reliably modulate phase-shifting effects of late night bright light in humans.

Adolescent↗