Relative humidity and affective disorders.

Introduction: Looking at specific weather parameters over a period of time prior to hospital admissions may provide evidence of a link between weather conditions and some psychiatric conditions such as affective disorders. We examined the association between relative humidity (as well as other parameters such as sunshine hours, diurnal variations in temperature and rainfall) and psychiatric admissions in North Cheshire, UK.

Method: The daily numbers of all psychiatric admissions in North Cheshire in a specified year were analysed in relation to meteorological data, which were measured at the meteorological office nearest to the study population.

Results: We found a significant inverse relationship (with time lag) between admissions for affective disorders and relative humidity in the week preceding admission. Changes in diurnal variations in temperature, sunshine hours and rainfall a few days before admission were also noted, but the findings did not achieve statistical significance for any diagnostic category.

Conclusion: The effect of weather parameters on mental health is likely to be influenced by other seasonal factors, as well as non-climatic factors, predominantly social, that may have contributed to the study findings. Psychiatric admissions reflect the behaviour of patients, carers and medical professionals. The complexity of this behaviour and the day-of-the-week periodicity may have confounded variations associated with the weather. (Int J Psych Clin Pract 2002; 6: 147-153 ).