Sleep, Serotonin, and Suicide in Japan

Abstract

This article reviews evidence supporting the hypothesis that suicide rates in Japan could be reduced by elevating serotonin levels via increasing the average duration of sleep. Seven major relevant findings were apparent in the literature: 1) Sleep loss is associated with suicide, but the direction of causality is equivocal. 2) Decreased serotonergic activity may be involved in suicidal behavior. 3) Sleep debt may decrease serotonergic activity. 4) The suicide rate in Japan has remained at a heightened level for the past 12 years. 5) The average sleep duration in Japan has decreased over the past 40 years. 6) The average sleep duration in Japan is among the lowest in the world. 7) The average sleep duration in Japan plateaued in 1995 and has been relatively stable since. From the research reviewed, two major problematic issues were apparent: 1) Most people in Japan receive inadequate sleep. 2) Individuals whose sleep is inadequate are unlikely to be sufficiently physically active to stimulate serotonergic systems to a desirable level. I propose that public health initiatives encouraging a longer duration of sleep may provide a relatively simple way of addressing the disturbing current trend in Japan. The combination of actigraph and brain serotonin level measurement could allow large population-based cohort studies to be designed, to elucidate the causal links between sleep duration, serotonin levels, and suicide rates.

Short Sleep Duration and Circadian Rhythms: Association with Suicidal Behaviour

“…Suicide is a complex behaviour and a serious public health problem, affecting all ages and socioeconomic groups, with severe implications to families and society [1][2][3]. The last records of the World Health Organization [4] report that suicide is responsible for more than 800 000 deaths per year worldwide, and the number of attempted but unsuccessful suicides clearly outdoes this [5].…”

“…Many risk factors have been associated with suicide [7][8][9][10], such as psychiatric disorders (depression being probably the most important risk factor [1]), impulsive or aggressive behaviour, family history of suicide, loss of a close friend or relative, physical or sexual abuse, lack of a support network, or sleep disturbances, especially with a chronic evolution [1,11]. Concerning this last factor, nightmares and insomnia have been consistently reported to increase the risk of suicidal behaviours, even after adjusting for depression severity (e.g.…”

“…In fact, sleep could actually influence mental health and the emergence of suicidal behaviours, since countries with the highest suicide rates, such as Japan and South Korea, are also the most "sleep deprived" countries [1,14]. This is thought to be related to cultural factors, more than biological features: people in these countries suffer more pressure to succeed at school and work, with more hours of labour, frequently falling into a state of chronic sleep deprivation [1].…”

“…This is thought to be related to cultural factors, more than biological features: people in these countries suffer more pressure to succeed at school and work, with more hours of labour, frequently falling into a state of chronic sleep deprivation [1]. Additionally, insomnia and suicidal behaviours seem to share some neurobiological pathways, including serotonergic dysregulation, alterations in the hypothalamic-pituitary-adrenal (HPA) axis, elevations in proinflammatory cytokines, and alterations in brain structure, namely in the prefrontal cortex [15,16].…”

“…Given the influence of sleep disorders over suicide risk [1], it is crucial to determine the role of those altered sleep habits in the development of suicidal behaviours.…”