Fatigue, susceptibility to the common cold and its behavioural effects.

The aim of the present article is to describe bi-directional interactions between fatigue and infection with common cold producing viruses. Over one hundred years ago, researchers started to investigate the association between been fatigue and infection. Studies of psychological risk factors for upper respiratory tract illnesses (URTIs) have been carried out for over fifty years. Early research did not control for exposure and also often relied on self-report rather than clinical and virological assessment. Research on experimentally-induced URTIs has demonstrated that susceptibility to infection is increased by stress. Other research has shown that job insecurity, few social contacts, emotional disposition, early childhood experiences, sleep problems and self-rated health are key risk factors for infection. This article provides an interpretation of these results in terms of chronic fatigue increasing susceptibility to infection. Infection and illness also lead to changes in behaviour. These effects include greater fatigue, impaired attention and slower motor speed. Such effects occur not only when the person has symptoms but in the incubation period, with sub-clinical infections, and after the symptoms have gone. Those with URTIs are also more sensitive to other negative factors such as prolonged work, and this has implications for safety-critical jobs. Ingestion of caffeine, which is an established countermeasure for fatigue, can reduce the behavioural malaise induced by URTIs. Further support for the use of a fatigue framework comes from a secondary analysis of data on real-life colds. Previous research has demonstrated that chronic fatigue leads to greater effects of acute fatigue. The new analysis showed that those with high levels of fatigue prior to developing a cold had larger behavioural impairments when they became ill