[Seasons, circadian rhythms, sleep and suicidal behaviors vulnerability]

Suicidal behaviors are common in the general population and are so a major public health problem. In order to improve suicide prevention and to reduce the mortality by suicide, it appears essential to better identify suicide risk factors. Seasonality, circadian rhythms and sleep abnormalities have been already associated with numerous psychiatric disorders. This review aimed to characterize the associations between seasonality, circadian rhythms, sleep and suicidal behaviors including suicide attempts and completed suicides.

We conducted a literature search between 1973 and 2015 in PubMed databases using the following terms: ("suicide" OR "suicidality" OR "suicide attempts" OR "suicidal behavior") AND ("circadian rhythms" OR "seasons" OR "sleep").

Many studies confirm a specific seasonality for suicide with a higher peak of suicides in spring for both sex and a lower peak in autumn especially for women. This distribution seems to correlate with depressive symptoms (especially for the autumn peak), gender and different types of suicide. Regarding gender and type of suicide differences, males more commonly commit violent suicide with a higher rate of suicides in spring. Suicide behaviors appear to be influenced by climatic and biological factors like sunshine, daylight cycles, temperature, air pollutants, viruses, parasites and aeroallergens. Circadian variations exist in suicide rates depending on age with a morning peak for elder and an evening peak for youth. In addition, completed suicide peak in early morning whereas suicide attempts peak rather in later afternoon. Several biomarkers dysregulation like melatonin, serotonin and cortisol may be implicated in suicide circadian variations. Furthermore, specific sleep disorders like insomnia, nightmares and sleep deprivation are common risk factors of suicide and possibly independently of the presence of depressive symptoms. Finally, the efficacy of chronotherapeutics (such as luminotherapy, dark therapy, sleep deprivation and melatonin drugs) has been suggested in the reduction of suicidal behaviors.

The suicide seasonality is very well documented showing a main peak in spring and another one in autumn. A suicide circadian distribution also exists depending of the suicidal behavior intensity and of the age. Numerous sleep disorders are also suicide risk factors and can be treated with chronotherapeutics. A better identification of seasonality, circadian rhythms and sleep abnormalities in suicidal behaviors could allow a better prevention in suicidal attempts and a reduction in death by suicide.