Longevity means living a long time in a good health and includes two essential factors: health and time. Health can be assessed by subjective and objective measures, and time by days and nights incorporated into circadian rhythm. Sun, as a source of light, is the major synchroniser of the circadian rhythm and biological clock of the humans and is the essential intrinsic dirigent of the multiple biological rhythms of the body, which impact the health.

Chronotherapeutics for Affective Disorders describes the impact of the environmental factor, light for the circadian rhythm and gives many practical recommendations for therapeutic interventions using the physiological resources: light and sleep/wake cycle.

The described interventions have practically no side effects, are cost-effective, can shorten the duration of the hospitalisation and can be used not only within the hospital, but also in outpatients and ambulatory settings.

Disorders in the periodicity of the circadian rhythm are very common for all affective disorders – ranging from seasonal, as in winter depression, to rapid cycling, diurnal variation of the mood, early morning awakening and sleep disturbances.

Wake therapy, light and melatonin have been shown as very potent biological tools and can re-set the circadian rhythm, improving the sleep and the mood.

The Book is a project of the centre for environmental therapeutics, which is an independent, non-profit professional agency dedicated to education and research on the new environmental therapies and the authors as distinguished experts are members of the board of directors.

The story about light therapy is 30 years old. Dr. Rosenthal described in one of his lectures (1984) the application of bright light in patients with seasonal depression. In the following 20 years, many studies with different settings examined the efficiency of the chronotherapeutics. The year 2005 was a signal year of the field with consensus achieved by an American psychiatric association work group that light can serve as a first-line treatment intervention for both seasonal and non-seasonal depression (Reference Golden, Gaynes, Ekstrom, Hamer, Jacobsen and Suppes1).

Emerging new data also suggest that light therapy can be used as a first-line treatment given together with the chosen antidepressant and that combination of light with drugs can accelerate the improvement, a method already in widespread use with European inpatients.

Morning light is superior to evening light and offers an important additional step towards reducing residual symptoms, lowering the probability of relapse at low costs and with minimal side effects.

Light therapy can be combined with wake therapy or sleep deprivation: authors describe several combination strategies of integrative chronotherapeutics using an algorhythm consisting of three steps: light therapy, followed by single wake night with light at the morning, and inclusion of 3-day sleep phase advance – as a third step.

Very impressive, the three-step strategy has been described using the case reports and sleep–wake diaries.

The slow response to the antidepressant is a big problem in the treatment of affective disorders and can be cope implementing the wake therapy with remarkable improvement. The response to a single wake therapy session occur in ∼60% of the patients with major depression whereas being awake in the second half of the night is crucial for the antidepressant response (Reference Wirz-Justice and Van den Hoofdakker2).

For the implementation of wake therapy in the inpatient setting, the nurses are key figures organising the night and day activities, reinforcing the motivation of the participants and creating a warm human environment at the department. Beside that patient education is crucial.

Although the risk for side effects using the light and wake therapy are very low, there are still some limitations: chronotherapeutics are potent neurobiological interventions that can worsen underlying manic state and indeed trigger rapid cycling but there is no data for increased suicidality. In the case of use of the photosensitising medications, bright light can damage the skin, cornea and lens.

There are only few contraindication for sleep deprivation as epilepsy and major medical illnesses (e.g. depressed cancer patient), as well as medication with antipsychotic and sedative drugs.

Interestingly, the predictors for response are the same as for antidepressant drugs: presence of diurnal mood fluctuation, melancholic features and previous history of response to any treatments, bipolar patients having a higher response rate than unipolar patients.

Which kind of light box to buy? The users should look for the light box, which have been tested in peer-reviewed clinical trials, providing up to 10 000 lx and should give off soft and broad-band white light rather than coloured light.

The authors are making statement about the premature marketing of blue augmentation in light therapy devices with unproved claims for clinical efficacy and mean that these devices cannot yet be recommended.

Not only for the treatment of affective disorders, the bright light therapy can also be implemented for a bright range of chronotherapeutic indications as ante partum depression, premenstrual dysphonic disorder, eating disorders, attention deficit hyperactivity disorder, dementia, shift work and jet lag disturbance.

Authors mention the complexity of shift work schedules as a big obstacle for implementing of such programme by industry describing it as a major challenge for applied chronobiology.

The last chapter is dedicated to the endogenous and exogenous melatonin describing its physiological effects of peripheral vasoconstriction (explaining the old fashioned methods to encourage a good nights sleep – a hot bath or footbath, warm drink, hot water bottle and bed socks). Against the usual recommendation of drug companies, the authors suggest that even low dose of melatonin (0.3 mg) can improve polysomnographically determined sleep efficiency as effectively as a high dose (5.0 mg).

Because of the rapid half-life of melatonin, the administration should follow few times in multiple low doses before the bed time.

Talking about genetic biomarkers the authors mention the role of the clock genes in the aetiology of the affective disorders whereas some genetic polymorphisms have been shown to influence core components of the illness such age of onset. The contemporary life style as epigenetical factor degrades the regularity and synchrony of circadian rhythms, which are so important for health and well-being by production of the artificial day inducing sleep disorders, depression and other illnesses.

The interpersonal social rhythm therapy is described as novel psychotherapeutic intervention using the principles of social rhythm therapy.

In the era of personalised medicine, clinicians should estimate the best timing for light therapy of each patient because the best response rates are achieved when individuals are treated according to their circadian phase (internal time). A primary marker for individual circadian phase is the circadian rhythm of melatonin, which is still not standardised for routine use, but timing and duration of the light application can be individually estimated using the MEQ Questionnaire for the individual chronotype (attached in this book).

An important message to the clinicians is that they should probe for chronotype whenever they meet a new patient.

Not only the doctors are aware of the need for light, even the famous architect le Corbusier recognised the implication of the light/darkness rhythm constructing the built environment!

One important question for the authors could be if light and wake therapy have the same antidepressant effect in people living in the Mediterranean country's….

Chronotherapeutics for Affective Disorders is an excellent manual for all clinicians who want to include the two sources of the energy in the treatment of their patients – light and circadian rhythm.