Fatigue science for human health

Abstract

What is fatigue? Why do we feel tired sometimes or seemingly all of the time? What is the physiological role or meaning of the sensation of fatigue ? How is chronic fatigue related to various diseases? How can we prevent chronic fatigue and exhaustion? In the past we really did not know very much about the mechanisms of fatigue. Fatigue is really an important bio-alarm, without which we might drop into an unrecoverable exhaustive state and in the most severe case even die, referred to in Japanese as Karoshi. As compared with the mechanisms of other bio-defense systems such as pain and fever, little is known regarding molecular/neuronal mechanisms of fatigue. Cytokine-prostaglandin systems are involved as the major factors in the induction and/or mediation of pain and fever. Although some pre-inflammatory cytokines may be the central mediator(s) in fatigue, Matsumura et al. will present their results indicating that the prostaglandin systems are probably not involved in the mechanisms of fatigue. Lactate, which was previously considered to be a candidate fatigue-inducing substance accumulating during severe exercise, is no longer thought to be a causative substance of fatigue. Although surprisingly a lot of people are suffering from chronic fatigue lasting longer than 6 months (more than one-third of the Japanese population), integrated research on fatigue had not been organized until our research projects under MEXT. Here, I would like to summarize the present status of fatigue research and am going to present the efforts to develop anti-fatigue foods, medicine, and daily life goods. [J Physiol Sci. 2008;58 Suppl:S18]