The interest in the systematic study of the circadian typology (CT) is relatively recent and has developed rapidly in the two last decades. All the existing data suggest that this individual difference affects our biological and psychological functioning, not only in health, but also in disease. In the present study, we review the current literature concerning the psychometric properties and validity of CT measures as well as individual, environmental and genetic factors that influence the CT. We present a brief overview of the biological markers that are used to define differences between CT groups (sleep-wake cycle, body temperature, cortisol and melatonin), and we assess the implications for CT and adjustment to shiftwork and jet lag. We also review the differences between CT in terms of cognitive abilities, personality traits and the incidence of psychiatric disorders. When necessary, we have emphasized the methodological limitations that exist today and suggested some future avenues of work in order to overcome these. This is a new field of interest to professionals in many different areas (research, labor, academic and clinical), and this review provides a state of the art discussion to allow professionals to integrate chronobiological aspects of human behavior into their daily practice.

Circadian typology: a comprehensive review.

The health impacts of environmental noise are a growing concern. At least one million healthy life years are lost every year from traffic-related noise in the western part of Europe. This publication summarises the evidence on the relationship between environmental noise and health effects, including cardiovascular disease, cognitive impairment, sleep disturbance, tinnitus, and annoyance. For each one, the environmental burden of disease methodology, based on exposure-response relationship, exposure distribution, background prevalence of disease and disability weights of the outcome, is applied to calculate the burden of disease in terms of disability-adjusted life-years. Data are still lacking for the rest of the WHO European Region. This publication provides policy-makers and their advisers with technical support in their quantitative risk assessment of environmental noise. International, national and local authorities can use the procedure for estimating burdens presented here to prioritize and plan environmental and public health policies.

Burden of Disease from Environmental Noise: Quantification of Healthy Life Years Lost in Europe

The role of noise as an environmental pollutant and its impact on health are being increasingly recognized. Beyond its effects on the auditory system, noise causes annoyance and disturbs sleep, and it impairs cognitive performance. Furthermore, evidence from epidemiologic studies demonstrates that environmental noise is associated with an increased incidence of arterial hypertension, myocardial infarction, and stroke. Both observational and experimental studies indicate that in particular night-time noise can cause disruptions of sleep structure, vegetative arousals (e.g. increases of blood pressure and heart rate) and increases in stress hormone levels and oxidative stress, which in turn may result in endothelial dysfunction and arterial hypertension. This review focuses on the cardiovascular consequences of environmental noise exposure and stresses the importance of noise mitigation strategies for public health.

https://www.klein-winternheim.de/lokale-agenda/d43d5e550c96630fc05d6c66ec88f0f4_Elsner-eurheartj.ehu030.full.pdf

Cardiovascular effects of environmental noise exposure

Based on the idea that electric light at night might account for a portion of the high and rising risk of breast cancer worldwide, it was predicted long ago that women working a non-day shift would be at higher risk compared with day-working women. This hypothesis has been extended more recently to prostate cancer. On the basis of limited human evidence and sufficient evidence in experimental animals, in 2007 the International Agency for Research on Cancer (IARC) classified 'shift work that involves circadian disruption' as a probable human carcinogen, group 2A. A limitation of the epidemiological studies carried out to date is in the definition of 'shift work.' IARC convened a workshop in April 2009 to consider how 'shift work' should be assessed and what domains of occupational history need to be quantified for more valid studies of shift work and cancer in the future. The working group identified several major domains of non-day shifts and shift schedules that should be captured in future studies: (1) shift system (start time of shift, number of hours per day, rotating or permanent, speed and direction of a rotating system, regular or irregular); (2) years on a particular non-day shift schedule (and cumulative exposure to the shift system over the subject's working life); and (3) shift intensity (time off between successive work days on the shift schedule). The group also recognised that for further domains to be identified, more research needs to be conducted on the impact of various shift schedules and routines on physiological and circadian rhythms of workers in real-world environments.

/pdf/considerations-of-circadian-impact-for-defining-shift-work-3hq51bdy7n.pdf

Considerations of circadian impact for defining 'shift work' in cancer studies: IARC working group report

Melatonin signals time of day and time of year in mammals by virtue of its pattern of secretion, which defines 'biological night.' It is supremely important for research on the physiology and pathology of the human biological clock. Light suppresses melatonin secretion at night using pathways involved in circadian photoreception. The melatonin rhythm (as evidenced by its profile in plasma, saliva, or its major metabolite, 6-sulphatoxymelatonin [aMT6s] in urine) is the best peripheral index of the timing of the human circadian pacemaker. Light suppression and phase-shifting of the melatonin 24 h profile enables the characterization of human circadian photoreception, and circulating concentrations of the hormone are used to investigate the general properties of the human circadian system in health and disease. Suppression of melatonin by light at night has been invoked as a possible influence on major disease risk as there is increasing evidence for its oncostatic effects. Exogenous melatonin acts as a 'chronobiotic.' Acutely, it increases sleep propensity during 'biological day.' These properties have led to successful treatments for serveal circadian rhythm disorders. Endogenous melatonin acts to reinforce the functioning of the human circadian system, probably in many ways. The future holds much promise for melatonin as a research tool and as a therapy for various conditions.

Melatonin and Human Rhythms

Noise emitted from road, rail and air traffic and their effects on sleep

The cortisol awakening response: a pilot study on the effects of shift work, morningness and sleep duration.

If applied during corresponding times of the individual melatonin profiles, bright light shifts the circadian phase equally, irrespective of diurnal type. We examined 32 young men: 10 morning types, 11 evening types, and 11 with no predisposition; 16 with high and 16 with low melatonin production. Each completed a 40 h session that included two consecutive nights during which the participants remained, apart from two short breaks during the second day, in bed under an illumination level of 30 lux. A 4 h bright light pulse was applied just after the expected individual melatonin onset the first night to cause a delay of the hormonal profile the second night. Salivary levels of melatonin and cortisol were determined hourly. Melatonin was delayed by 108 min, and cortisol offset and onset by 47 and 110 min, respectively. The cortisol quiescent period (start and end of the quiescent period being defined by the decrease below and the increase above 60% of the average cortisol production between 18:00 and 09:00 h) was prolonged. In contrast to the other subgroups, the delay of melatonin synthesis was about 0.5 h shorter in morning types, and their cortisol quiescent period was shortened. The present study leads to the hypothesis that, despite individually scheduled light exposure, morning types are potentially disadvantaged due to elevated cortisol levels, if persisting, in career night workers.

Shifts of the hormonal rhythms of melatonin and cortisol after a 4 h bright-light pulse in different diurnal types.

Cortisol awakening response (CAR), a considerable increase in cortisol concentrations post-awakening, is considered a reliable indicator of the reactivity of the hypothalamus-pituitary-adrenal axis (HPA). As noise has been shown to activate the HPA-axis, this analysis focuses on CAR as a possible indicator of noise-induced sleep disturbances. This analysis focuses on CAR using two studies. In Study 1, six women and six men (18-26 years) slept for 13 nights each in the laboratory. They were exposed to the noises of three different trains, each with 20, 40 or 80 pass-bys, with equivalent noise levels varying between 44 and 58 dBA, on nine nights. In Study 2, 23 persons slept first for four nights and then four days, in the laboratory; finally 23 persons slept in the reverse order. During six sleep periods, they were randomly exposed to road or rail traffic noises with L Aeq varying between 42 and 56 dBA. To determine the CAR, salivary cortisol concentrations were ascertained in both studies after night sleep immediately after awakening, and 15 and 45 minutes later; in Study 2 also after 30 and 60 minutes later. The time of awakening was determined using the polysomnogram and the participants rated their subjective sleep quality every morning. Subjective sleep quality was rated worse after noisy when compared to quiet nights. CAR was, however, attenuated only after the noisiest nights in a subgroup of Study 2. These persons had just performed a sequence of four consecutive night shifts. They were obviously still in the process of re-adjustment to their usual day-oriented schedule and probably in a state of elevated vulnerability. The study concludes that nocturnal noise exposure affects the CAR only if a person is in a state of at least temporarily elevated vulnerability.

Experimental studies on the effects of nocturnal noise on cortisol awakening response

This analysis was aimed at the development of a sleep disturbance index (SDI) which allows a reliable estimate of physiological sleep disturbances due to environmental influences such as noise. Seven variables, repeatedly reported to change during noise exposure, were derived from polysomnograms of a reference sample of 38 men and 28 women (19–34 yrs) as recorded under quiet conditions in the laboratory after at least one habituation night. The variables were then submitted to a principal component analysis. The scores of the first principal component that explained 35 % of the variance were used to calculate the SDI. Reliability was ascertained by application of the SDI to a quiet night for each of 82 persons of the same age range from two other laboratory studies where the index value did not differ from that of the reference sample. Validity was verified by significantly lower index values for quiet nights than for noisy nights of 50 persons (25 men, 25 women, 19–28 yrs) and for the first night in the laboratory of 62 persons (37 men, 25 women, 19–34 yrs). Moreover, the index value increased with increasing age of the 261 participants in two laboratory studies and a field study whose age varied between 18 and 68 years. The SDI may facilitate the interpretation of sleep disturbances caused by environmental influences and its application would improve the comparability of studies performed in this area.

Sibylle Robens

Papers

Noise emitted from road, rail and air traffic and their effects on sleep

The cortisol awakening response: a pilot study on the effects of shift work, morningness and sleep duration.

Shifts of the hormonal rhythms of melatonin and cortisol after a 4 h bright-light pulse in different diurnal types.

Experimental studies on the effects of nocturnal noise on cortisol awakening response

Development of a sleep disturbance index (SDI) for the assessment of noise-induced sleep disturbances