Journal of Circadian Rhythms - Most accessed articles

Differential roles of breakfast only (one meal per day) and a bigger breakfast with a small dinner (two meals per day) in mice fed a high-fat diet with regard to induced obesity and lipid metabolism

Yuta Fuse — 2012-05-15T00:00:00Z

Background: Recent studies on humans and rodents have suggested that the timing of food intake plays an important role in circadian regulation and metabolic health. Consumption of high-fat foods during the inactive period or at the end of the awake period results in weight gain and metabolic syndrome in rodents. However, the distinct effects of breakfast size and the breakfast/dinner size ratio on metabolic health have not yet been fully examined in mice. Methods: We examined whether the parameters of metabolic syndrome were differentially affected in mice that consumed a large meal at the beginning of the awake period (breakfast; one meal group) and a relatively smaller meal at end of the awake period (dinner; two meals group).The mice of each group were provided equal food volume per day. Results: Mice on one meal exhibited an increase in body weight gain, hyperinsulinemia, hyperleptinemia, and a decrease of gene expression associated with beta-oxidation in adiposetissue and liver compared with those on two meals. The circadian expression pattern of the Clock gene in mice on one meal was disturbed compared with those on two meals. Conclusions: In conclusion, a bigger breakfast with a smaller dinner (two meals per day) but not breakfast only (one meal per day) helps control body weight and fat accumulation in mice on a high-fat meals schedule. The findings of this study suggest that dietary recommendations for weight reduction and/or maintenance should include information on the timing and quantity of dietary intake.

Summer activity patterns among teenage girls: harmonic shape invariant modeling to estimate circadian cycles

Semhar Ogbagaber — 2012-05-06T00:00:00Z

Background: Physical activity as measured by activity counts over short time intervals across a 24 h periodare often used to assess circadian variation. We are interested in characterizing circadianpatterns in activity among adolescents and examining how these patterns vary by obesitystatus. New statistical approaches are needed to examine how factors affect different featuresof the circadian pattern and to make appropriate covariate adjustments when the outcomes arelongitudinal count data. Methods: We develop a statistical model for longitudinal or repeated activity count data that is used toexamine differences in the overall activity level, amplitude (defined as the difference betweenthe lowest and highest activity level over a 24 hour period), and phase shift. Using seven daysof continuous activity monitoring, we characterize the circadian patterns and compare thembetween obese and non-obese adolescent girls. Results: We find a statistically significant phase delay in adolescent girls who were obese comparedwith their non-obese counterparts. After the appropriate adjustment for measured potentialconfounders, we did not find differences in mean activity level between the two groups. Conclusion: New statistical methodology was developed to identify a phase delay in obese compared withnon-obese adolescents. This new approach for analyzing longitudinal circadian rhythm countdata provides a useful statistical technique to add to the repertoire for those analyzingcircadian rhythm data.

Neurotransmitters of the suprachiasmatic nuclei

Vallath Reghunandanan — 2006-02-16T00:00:00Z

There has been extensive research in the recent past looking into the molecular basis and mechanisms of the biological clock, situated in the suprachiasmatic nuclei (SCN) of the anterior hypothalamus. Neurotransmitters are a very important component of SCN function. Thorough knowledge of neurotransmitters is not only essential for the understanding of the clock but also for the successful manipulation of the clock with experimental chemicals and therapeutical drugs. This article reviews the current knowledge about neurotransmitters in the SCN, including neurotransmitters that have been identified only recently. An attempt was made to describe the neurotransmitters and hormonal/diffusible signals of the SCN efference, which are necessary for the master clock to exert its overt function. The expression of robust circadian rhythms depends on the integrity of the biological clock and on the integration of thousands of individual cellular clocks found in the clock. Neurotransmitters are required at all levels, at the input, in the clock itself, and in its efferent output for the normal function of the clock. The relationship between neurotransmitter function and gene expression is also discussed because clock gene transcription forms the molecular basis of the clock and its working.

Circadian rhythm and its role in malignancy

Sobia Rana — 2010-03-31T00:00:00Z

Circadian rhythms are daily oscillations of multiple biological processes directed by endogenous clocks. The circadian timing system comprises peripheral oscillators located in most tissues of the body and a central pacemaker located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Circadian genes and the proteins produced by these genes constitute the molecular components of the circadian oscillator which form positive/negative feedback loops and generate circadian rhythms. The circadian regulation extends beyond clock genes to involve various clock-controlled genes (CCGs) including various cell cycle genes. Aberrant expression of circadian clock genes could have important consequences on the transactivation of downstream targets that control the cell cycle and on the ability of cells to undergo apoptosis. This may lead to genomic instability and accelerated cellular proliferation potentially promoting carcinogenesis. Different lines of evidence in mice and humans suggest that cancer may be a circadian-related disorder. The genetic or functional disruption of the molecular circadian clock has been found in various cancers including breast, ovarian, endometrial, prostate and hematological cancers. The acquisition of current data in circadian clock mechanism may help chronotherapy, which takes into consideration the biological time to improve treatments by devising new therapeutic approaches for treating circadian-related disorders, especially cancer.

The effect of high correlated colour temperature office lighting on employee wellbeing and work performance

Peter Mills — 2007-01-11T00:00:00Z

Background: The effects of lighting on the human circadian system are well-established. The recent discovery of 'non-visual' retinal receptors has confirmed an anatomical basis for the non-image forming, biological effects of light and has stimulated interest in the use of light to enhance wellbeing in the corporate setting. Methods: A prospective controlled intervention study was conducted within a shift-working call centre to investigate the effect of newly developed fluorescent light sources with a high correlated colour temperature (17000 K) upon the wellbeing, functioning and work performance of employees. Five items of the SF-36 questionnaire and a modification of the Columbia Jet Lag scale, were used to evaluate employees on two different floors of the call centre between February and May 2005. Questionnaire completion occurred at baseline and after a three month intervention period, during which time one floor was exposed to new high correlated colour temperature lighting and the other remained exposed to usual office lighting. Two sided t-tests with Bonferroni correction for type I errors were used to compare the characteristics of the two groups at baseline and to evaluate changes in the intervention and control groups over the period of the study. Results: Individuals in the intervention arm of the study showed a significant improvement in self-reported ability to concentrate at study end as compared to those within the control arm (p < 0.05). The mean individual score on a 5 point Likert scale improved by 36.8% in the intervention group, compared with only 1.7% in the control group. The majority of this improvement occurred within the first 7 weeks of the 14 week study. Substantial within group improvements were observed in the intervention group in the areas of fatigue (26.9%), alertness (28.2%), daytime sleepiness (31%) and work performance (19.4%), as assessed by the modified Columbia Scale, and in the areas of vitality (28.4%) and mental health (13.9%), as assessed by the SF-36 over the study period. Conclusion: High correlated colour temperature fluorescent lights could provide a useful intervention to improve wellbeing and productivity in the corporate setting, although further work is necessary in quantifying the magnitude of likely benefits.

Transdisciplinary unifying implications of circadian findings in the 1950s

Franz Halberg — 2003-10-29T00:00:00Z

A few puzzles relating to a small fraction of my endeavors in the 1950s are summarized herein, with answers to a few questions of the Editor-in-Chief, to suggest that the rules of variability in time complement the rules of genetics as a biological variability in space. I advocate to replace truisms such as a relative constancy or homeostasis, that have served bioscience very well for very long. They were never intended, however, to lower a curtain of ignorance over everyday physiology. In raising these curtains, we unveil a range of dynamics, resolvable in the data collection and as-one-goes analysis by computers built into smaller and smaller devices, for a continued self-surveillance of the normal and for an individualized detection of the abnormal. The current medical art based on spotchecks interpreted by reference to a time-unqualified normal range can become a science of time series with tests relating to the individual in inferential statistical terms. This is already doable for the case of blood pressure, but eventually should become possible for many other variables interpreted today only based on the quicksand of clinical trials on groups. These ignore individual differences and hence the individual's needs. Chronomics (mapping time structures) with the major aim of quantifying normalcy by dynamic reference values for detecting earliest risk elevation, also yields the dividend of allowing molecular biology to focus on the normal as well as on the grossly abnormal.

Time for sex: nycthemeral distribution of human sexual behavior

Roberto Refinetti — 2005-03-24T00:00:00Z

Background: Nycthemeral (daily) oscillation has been documented in a variety of physiological and behavioral processes. The present study was carried out to evaluate the existence of a nycthemeral rhythm of human sexual behavior and to identify environmental factors responsible for the rhythmic pattern. Methods: Non-traditional university students (ages 18 to 51 years) recorded the times of day when they went to sleep, when they woke up, and when they had sex for 3 consecutive weeks. They also answered a questionnaire designed to identify the causes of their selection of time for sex. Results: The majority of sexual encounters took place at bedtime (11 pm to 1 am). The most common explanations for this temporal pattern were the rigidity of the professional work schedule and family obligations and the availability of the partner, which reduced the opportunity for sexual encounters at other times of the day. Conclusion: Most sexual encounters take place around bedtime. Although the presence of an endogenous component responsible for this temporal pattern cannot be excluded, the evidence indicates strong environmental forcing, particularly from the work/family schedule of the individuals and from partner availability.

Circadian light

Mark Rea — 2010-02-13T00:00:00Z

The present paper reflects a work in progress toward a definition of circadian light, one that should be informed by the thoughtful, century-old evolution of our present definition of light as a stimulus for the human visual system. This work in progress is based upon the functional relationship between optical radiation and its effects on nocturnal melatonin suppression, in large part because the basic data are available in the literature. Discussed here are the fundamental differences between responses by the visual and circadian systems to optical radiation. Brief reviews of photometry, colorimetry, and brightness perception are presented as a foundation for the discussion of circadian light. Finally, circadian light (CLA) and circadian stimulus (CS) calculation procedures based on a published mathematical model of human circadian phototransduction are presented with an example.

Evolution of temporal order in living organisms

Dhanashree Paranjpe — 2005-05-04T00:00:00Z

Circadian clocks are believed to have evolved in parallel with the geological history of the earth, and have since been fine-tuned under selection pressures imposed by cyclic factors in the environment. These clocks regulate a wide variety of behavioral and metabolic processes in many life forms. They enhance the fitness of organisms by improving their ability to efficiently anticipate periodic events in their external environments, especially periodic changes in light, temperature and humidity. Circadian clocks provide fitness advantage even to organisms living under constant conditions, such as those prevailing in the depth of oceans or in subterranean caves, perhaps by coordinating several metabolic processes in the internal milieu. Although the issue of adaptive significance of circadian rhythms has always remained central to circadian biology research, it has never been subjected to systematic and rigorous empirical validation. A few studies carried out on free-living animals under field conditions and simulated periodic and aperiodic conditions of the laboratory suggest that circadian rhythms are of adaptive value to their owners. However, most of these studies suffer from a number of drawbacks such as lack of population-level replication, lack of true controls and lack of adequate control on the genetic composition of the populations, which in many ways limits the potential insights gained from the studies. The present review is an effort to critically discuss studies that directly or indirectly touch upon the issue of adaptive significance of circadian rhythms and highlight some shortcomings that should be avoided while designing future experiments.

CLOCK is suggested to associate with comorbid alcohol use and depressive disorders

Louise Sjoholm — 2010-01-21T00:00:00Z

Background: Depression and alcohol abuse or dependence (AUD) co-occur in the general population more frequently than expected by chance. Alcohol use influences the circadian rhythms generated by the central pacemaker in the suprachiasmatic nucleus, and circadian rhythm alterations in turn are common in depressive disorders as well as among persons addicted to alcohol. Methods: 32 SNPs in 19 circadian clockwork related genes were analyzed using DNA from 76 individuals with comorbid depression and AUD, 446 individuals with AUD and 517 healthy controls with no psychiatric diagnosis. The individuals participated in a nationwide health examination study, representative of the general population aged 30 and over in Finland. Results: The CLOCK haplotype TTGC formed by SNPs rs3805151, rs2412648, rs11240 and rs2412646, was associated with increased risk for comorbidity (OR = 1.65, 95% CI = 1.14-2.28, P = 0.0077). The SNPs of importance for this suggestive association were rs2412646 and rs11240 indicating location of the functional variation in the block downstream rs2412648. There was no indication for association between CLOCK and AUD. Conclusion: Our findings suggest an association between the CLOCK gene and the comorbid condition of alcohol use and depressive disorders. Together with previous reports it indicates that the CLOCK variations we found here may be a vulnerability factor to depression given the exposure to alcohol in individuals having AUD.